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Full text of "Byte Magazine Volume 02 Number 03 - Inexpensive Joystick Interfaces (RESCAN)"

MARCH 1977 



VOLUME 2, Number 3 




$1.50 

C A/l/ , 

T6$ 

Fuji- 



- A i-\ 






the small systems journal 




WHY SETTLE FOR LESS- 
THAN A 6800 SYSTEM 



MEMORY- 



All static memory with selected 2102 IC's al 
lows processor to run at its maximum 
speed at all times. No refresh system is 
needed and no time is lost in me- 
mory refresh cycles. Each board 
holds 4,096 words of this 
proven reliable and trouble 
free memory. Cost- 
only $125.00 for 
each full 4K 
memory. 



INTERFACE- 

Serial control interface connects to any RS-232, or 
20 Ma. TTY control terminal. Connectors pro- 
vided for expansion of up to eight interfaces. 
Unique programmable interface circuits 
allow you to match the interface to al- 
most any possible combination of 
polar i ty and control signal ar- 
rangements. Baud rate selec- 
tion can be made on each 
individual interface. All 
this at a sensible cost 
of only $35.00 for 
either serial, or 
parallel type 




"Motorola" M6800 processor 
with Mikbug® ROM operating 
system. Automatic reset and load- 
ing, plus full compatability with 
Motorola evaluation set software. Crystal 
controlled oscillator provides the clock signal 
for the processor and is divided down by the 
MC1441 1 to provide the various Baud rate outputs 
for the interface circuits. Full buffering on all data 
and address busses insures "glitch" free operation with 
full expansion of memory and interfaces. 

DOCUMENTATION- 

Probably the most extensive and complete set of data available for any 
microprocessor system is supplied with our 6800 computer. This includes 
the Motorola programming manual, our own very complete assembly in- 
structions, plus a notebook full of information that we have compiled on 
the system hardware and programming. This includes diagnostic programs, 
sample programs and even a Tic Tac Toe listing. 



POWER 
SUPPLY- 

Heavy duty 10.0 Amp power 

supply capable of powering a 

fully expanded system of memory 

and interface boards. Note 25 Amp 

rectifier bridge and 91 ,000 mfd computer 

grade filter capacitor. 



Mikbug*® is a registered trademark of 
Motorola Inc. 



Computer System 
with serial interface and 4,096 words 
of memory $395.00 



I" 




□ Enclosed is $395 for my SwTPC Computer Kit □ Send Data 

□ or BAG # 

□ or MC Ex Date 



NAME 



ADDRESS 



CITY STATE ZIP 

Southwest Technical Products Corp., Box 32040, San Antonio, Texas 78284 




Meet the most powerful 
AtC system available for dedicated work. 



Yet it's only $595: 



*kit price 



Here's the muscle you've been telling us you 
wanted: a powerful Cromemco microcomputer in a 
style and price range ideal for your dedicated com- 
puter jobs — ideal for industrial, business, instru- 
mentation and similar applications. 

It's the new Cromemco Z-2 Computer System, 
In the Z-2 you get all of the following for only $595: 

• The industry's fastest ,/*P board (4 MHz or 250- 
nanosecond cycle time). 

• The power and convenience of the well-known 
Z-80 |iP. 

• A power supply you won't believe ( + 8V @ 30A, 
+ 18V and -18V @ 15A. That's not only ample 
power for a full set of cards but ample additional 
power for other peripherals such as floppy disk 
drives). 

• A full-length shielded motherboard with 21 card 
slots to let you plug in almost any conceivable 
combination of memory, I/O or your own cus- 
tom circuits. 

• Power-on-jump circuitry to begin automatic pro- 
gram execution when power is 

turned on. 

• The S-100 bus that's widely 
supported by a host of pe- 
ripherals manufacturers. 

• All-metal chassis and 
dust case. 



• Standard rack-mount style construction that's 
usable with a variety of cabinets and is upward 
compatible with larger systems. Bench cabinet 
optional. 

• Card retainer to secure cards in sockets under all 
conditions. 

• 110- or 220-volt operation. 

DEDICATED APPLICATIONS 

The new Z-2 is specifically designed as a powerful 
but economical dedicated computer for systems 
work. Notice that the front panel is entirely free of 
controls or switches of any kind. That makes the 
Z-2 virtually tamper-proof. No accidental program 
changes or surprise memory erasures. 

(For your custom work, Cromemco will supply 
blank panels.) 

4 MHz SPEED 

Cromemco's microcomputers are the fastest and 
most powerful available. The 4 MHz speed of the 
Z-2 means you get about twice the speed of nearly 
any other microcomputer. 

(continued on next page) 





Cromemco 




Full-width motherboard 
has slots for 21 cards. 




Z-2 is supplied for rack mounting. 
Attractive bench cabinet shown is 
also available. 




Heavy-duty retainer bar insures that 
cards won't jostle out of sockets. 



That 4 MHz speed cuts running time in half — cuts 
your waiting time in half. Lets you do more sophisti- 
cated work that might not otherwise be practical with a 
microcomputer. 

Z-80 GIVES MORE COMPUTER POWER 

The Z-2 uses the powerful Z-80 microprocessor with 
its 158-instruction set, 19 internal registers, 10 address- 
ing modes, and 16 bit arithmetic operations. 

The Z-80 is widely regarded as the standard micro- 
processor of the future. So you're in the technical fore 
with the Z-2. But you can also plug in other micro- 
processor boards if you wish. 

BROAD SOFTWARE SUPPORT 

Since the Z-2 uses the Z-80, your present 8080 soft- 
ware can be used with the Z-2. In addition, Cromemco 
also offers software support including a monitor, assem- 
bler, and a BASIC interpreter. 

STANDARD S-100 BUS 

The Z-2 uses the S-100 bus that has become standard 
in the microcomputer field. Dozens of manufacturers 
support it with compatible peripherals. 

Of course, all Cromemco peripherals such as our 
7-channel A/D and D/A converter, our well-known 
BYTESAVER with its built-in PROM programmer, our 
color graphics interface, etc., will also plug into the bus. 

LOW NOISE 

Cromemco engineers have been careful to design 
the Z-2 for reliable operation at its fast 4 MHz speed. 
Noise on the motherboard, for example, has been care- 
fully minimized by a unique ground-plane design (we 
call it our 'Blitz Bus™'). With this bus you won't get 
erratic operation due to ground current noise. 

RACK OR CABINET MOUNTING 

The basic Z-2 is supplied in a black-anodized metal 
case for mounting in a standard 19-inch relay rack. A 
high-quality stylized bench cabinet in an attractive blue 
color is also available. 

KIT OR ASSEMBLED 

You can get the Z-2 either kit or assembled. The kit 
includes the Z-2 for rack mounting, the Cromemco 
4 MHz microprocessor card, full-length 21 -card-slot 
motherboard, power supply, one card socket and card- 
guide set, and front panel. 

The assembled Z-2 includes the above as well as all 
21 sockets and card guides and a cooling fan. 

LOW, LOW PRICE 

All who've seen the Z-2 have been surprised and 
impressed with its low price. 

You'll be impressed, too, with its technical excellence 
and quality. 

So see it right away at your computer store — or order 
now directly from the factory. 

The sooner you put this advanced computer to work 
for you, the sooner you'll be solving problems and 
saving time/ money. 

Z-2 Computer System kit (Model Z-2K) ..... $595. 
Z-2 Computer System assembled 

(Model Z-2W) $995. 



rj| Cromemco 



Specialists in computers and peripherals 

2432 CHARLESTON RO., MOUNTAIN VIEW, CA 94043 • (415) 964-7400 



BITE 



In the Queue 



70 

88 

106 

122 



9 
18 
26 
38 
50 
114 



4 

13 

14 

16 

36 

98, 104 
102 
113 
130 

136, 146 
137 
140 
142 
160 
160 



— 



Foreground 



SIMPLIFIED OMEGA RECEIVER DETAILS 

Hardware— Burhans 
INEXPENSIVE JOYSTICK INTERFACES 

Hardware— Busch bach 
FLIGHTS OF FANCY WITH THE ENTERPRISE 

Games Software— Price 
MULTIPLEX YOUR DIGITAL LED DISPLAYS 

Hardware— Hogenson 



Background 



GIVE YOUR MICRO SOME MUSCLES 

Hardware— Grappel 
REVIEW OF THE SWTPC PR-40 ALPHANUMERIC PRINTER 

Product Description— Kay 
CASSETTE TRANSPORTS FOR THE "ROLL YOUR OWN" HOBBYIST 

Cassette Transports— Freeman 
THE DIGITAL CASSETTE SUBSYSTEM, Part 2 

Hardware— Bremeir-R ampi I 
WHAT'S INVOLVED IN KIT BUILDING? 

Construction— Frenzel 
TRY THIS COMPUTER ON FOR SIZE 

Review— Ciarcia 



Nucleus 



In This BYTE 

PAPERBYTES™ Forum 

BYTE Goes International 

Letters 

A 6502 Op Code Table 

What's New? 

Technical Forum 

Positively Baker Street 

Another PAPERBYTES™ Test 

BYTE'sBits 

BYTE's Bugs 

Classified Ads 

Clubs, Newsletters 

BOMB 

Reader Service 




BYTE magazine is published 
monthly by BYTE Publica- 
tions, Inc, 70 Main St, Peter- 
borough, New Hampshire 
03458. Subscription rates are 
$12 for one year, $22 for two 
years, $30 for three years in 
North America. Second class 
postage paid at Peterborough 
New Hampshire 03458 and at 
additional mailing offices. 
Phone 603—924-7217. Entire 
contents copyright © 1977 
BYTE Publications, Inc, Peter- 
borough NH 03458. AU rights 
reserved. Address editorial cor- 
respondence to Editor, BYTE, 
70 Main St, Peterborough NH 
03458. Opinions expressed by 
authors are not necessarily 
those of BYTE magazine. 



MARCH 1977 
Volume 2 
Number 3 



PUBLISHERS 

Virginia Peschke 

Manfred Peschke 

EDITOR 

Carl T Helmers Jr 

PRODUCTION MANAGER 

Judith Havey 

CIRCULATION MANAGER 

Manfred Peschke 

ASSISTANT PUBLISHER 

Debra Boudrieau 

CO-OP EDITORS 

Scott Morrow 

Dan Pagan 

PRODUCTION EDITOR 

Karen Gregory 

CIRCULATION 

Kimberly Barbour 

Cheryl Hurd 

Deborah R Luhrs 

Carol Nyland 

Deena Zealy 

ADVERTISING 

Elizabeth Alpaugh 

Virginia Peschke 

ART 

Matthew Arnold 

Noreen Bardsley 

Mary Jane Frohlich 

Lynn Malo 

Bill Morello 

SPECIAL PRODUCTS 

Susan Pearne 

Floyd Rehling 

TYPOGRAPHY 

Custom Marketing Resources Inc 

Goodway Graphics 

Mary Lavoie 

Taimi Woodward 

PHOTOGRAPHY 

Ed Crabtree 

Custom Marketing Resources Inc 

PRINTING 

The George Banta Company 

Custom Marketing Resources Inc 

Lennie Cashion 

Larry Davis 

Jeff Pratt 

ASSOCIATES 

Bob Baker 

Walter Banks 

Steve Ciarcia 

Dan Fylstra 

Portia Isaacson 

Harold A Mauch 

CLUBS, CLASSIFIED 

Peter Travisano 

AFFILIATE PUBLISHER 

Southeast Asian Editions 

John Bannister 



page 26 




page 9 

In This 
BITE 

Many of the possible applications 
of small computers involve the moving 
of a mechanical device. One possible 
way to digitally control these devices 
is with servomechanisms such as those 
used in radio controlled model air- 
craft. In his article, Give Your Micro 
Some Muscles, Robert D Grappel 
describes how simple it is to interface 
these devices with your computer to 
control your own mechanical devices. 

Since microprocessors have hit the 
hobby market, one of the larger diffi- 
culties of the computer hacker has 
been obtaining inexpensive hardware 
copy capabilities. Southwest Technical 
Products Corp has introduced a line 
printer that is the answer to this 
difficulty. Their inexpensive impact 
dot matrix printer is described by 
Gary Kay in his article A Review of 
the SWTPC PR-40 Alphanumeric 
Printer. 

page 88 





The audio cassette is a kluge similar 
to paper tape; it works but is incon- 
venient. The "ideal" cassette system is 
completely controlled by the com- 
puter's commands, the full digital cas- 
sette recording facility. In his article 
on Cassette Transports for the "Roll 
Your Own" Hobbyist, William H 
Freeman takes a look at three dif- 
ferent drives which have potential as 
mass storage subsystems for the per- 
sonal computing experimenter. 

Last month we began an article on 
The Digital Cassette Subsystem, by 
Jack Breimeir and Ira Rampil. In this 
issue, we continue the discussion with 
part 2, concerning digital data formats 
and system considerations. 

Today's computer hobby world is a 
kit oriented one. In his article, Kit 
Building for the Computer Hobbyist, 
Louis E Frenzel sets forth guidelines 
that allow the inexperienced kit 
builder, the inexperienced hardware 
person, or the software hacker who 
just wants to get the basics, to con- 
struct a working computer oriented kit 
on the first attempt. 

Navigation has come a long way 
since the astrolabe, as exemplified by 
the Omega system. In this month's 
BYTE, Ralph W Burhans continues his 
presentation of the hardware for an 
inexpensive Omega navigation system 
with some Simplified Omega Receiver 
Details. (The series concludes with an 
article on software by Richard J Salter 
Jr in next month's BYTE.) 



About the Cover 

This month's cover is by Sandra D 
Crandall, Narragansett Rl 02882, a 
first prize winner of BYTE's Computer 
Art Contest. When she painted her 
updated "American Gothic/' she was 
completing her BFA in Art at the 
University of Rhode Island, and as 
assistant Art Department slide curator, 
maintained a library of over 40,000 
slides. "My fiance is finishing his BS in 
Computer Science and is an avid 
BYTE subscriber from the word go," 
she wrote. 



To interact with video games or 
graphic systems, it is often useful to 
interface devices such as joysticks to 
the microprocessor. In his article, An 
Inexpensive Joystick Interface, 
Thomas Buschbach describes one 
method that will enable you to imple- 
ment the conversion process in 
hardware. 

Over the years since the demise of 
the original Star Trek television series, 
there has been an increasing variety of 
people enamored with the ideas that 
the program had to offer. Among 
these people are personal computing 
enthusiasts who have turned these 
ideas into a large variety of computer 
games. In Flights of Fancy with the 
Enterprise, David Price introduces his 
own version of the Star Trek theme. 
His program, though small enough to 
be played on many microcomputers, 
allows a wide enough number of 
variations in play to satisfy even the 
most frequent users. This program is a 
must for Trekkies. 

Steve Ciarcia owns and uses a 
Digital Group 8080A system. Read • 
about his experiences and you might 
want to Try This Computer on for 
Size. 

Want 16 digit BCD output for your 
calculator software? Need an octal 
display to replace your binary lamps? 
Read Jim Hogenson's article on how 
to Multiplex Your Digital LED Dis- 
plays to find out what it takes to make 
numeric display output hardware. 






Introducing Sol Systems 

A complete computer/terminal 
concept with all the 
standard features, software 
and peripheral gear you 
want in your 
personal computer. 



\2fl*i«*^ 




IS^Ki^y 



Sol Systems put it all together. 

One source for hardware and software. 

One source for 

engineered compatibility 

of computer and peripherals. 

That's the Sol plan. 



Though the microprocessor made the 
powerful small computer possible, a lot of 
folks found out early efforts in the market- 
place were selling the sizzle a lot more than 
the steak. After an initial investment of sev- 
eral hundred dollars, you ended up with 
some nice parts, but no memory of any kind, 
no I/O devices or interfaces, no display, print- 
out or software. 

The Sol plan ends all that. Processor 
Technology takes the position that it's far 
better to be right than first. So let's get down 
to the Sol no tricks plan. 

For $995 in kit form, the first complete 
small computer 

Standard is a basic word at Processor 
Technology. The Sol-20 has more standard 
features than any other small computer we 
know of. Here's what you get. 

8080 microprocessor* 1024 character 
video display circuitry* 1024 words of static 
low-power RAM* 1024 words of prepro- 
grammed PROM* a custom, almost sensual 
85-key solid-state keyboard* audio cassette 
interface capable of controlling two record- 
ers at 1200 baud* both parallel and serial 
standardized interface connectors* a com- 
plete power supply* a beautiful case with 
solid walnut sides* software which includes 
a preprogrammed Prom personality module 
and a cassette with Basic-5 language plus 
two sophisticated computer video games* 
the ability to work with all S-100 bus 
(Altair 8800/IMSAI/PTC) products. 

There are no surprises. Everything 
you need to make it work is here. In kit 
form, nominal assembly time from our fully 
documented instructions is four to seven 
evenings. 

Or start with the Sol-PC for just $475 

You can begin your Sol system with the 
all on one board Sol-PC kit. It has all the 



memory and interface electronics including 
video display, keyboard interface, audio 
cassette interface, all necessary software 
and the ability to accept the full Processor 
Technology line of memory and interface 
modules. Use the Sol-PC as the basis of a 
microcomputer, low cost CRT terminal or 
editing terminal 



The Sol plan, completely expandable. 

By filling the basic main frame with 
tailor made Processor Technology plug-in PC 
boards, you can really expand the computing 
power and flexibility of your Sol-20 Personal 
Computer. 

New items are being announced fre- 
quently, but right now, here are some of the 
things you can add to your Sol-20. The 
ALS-8 Firmware module is an assembly 
language operating system to give you the 
power to develop and run programs. Use 
it to quickly write, edit, assemble, de-bug 
and run your own programs. Some say it's 
the most useful software development on the 
market today, but modesty prohibits. 

And when it comes to add-on memory 
boards, you've come to the right place. 
We've probably got more than anyone else. 
Choose from 2K ROM or 4, 8 or 16K RAM. 
The PT 2KRO will accept up to eight 1702A or 
5203Q erasable, reprogrammable memories 
(EPROM's) with the ability to store in a non- 
volatile fashion up to 2048 eight-bit words. 

Our read/write memories are the 
industry standards for high reliability. We 
know, because we have literally scores of 
customer letters saying "Your memory 
modules work and keep on working." 



A full line of Sol-20 tailored peripherals 

No computer can do the full job with- 
out the right set of peripheral gear. PT has 






sought out the best manufacturers of periph- 
eral equipment and worked with them to 
give you a choice of quality so you can get 
the most out of your Sol-20. Choose from 
line and serial printers, perforated tape 
readers and punches, floppy disk memories, 
black and white or color graphics displays, 
A/D, D/A converters and more. 

Software, the Computer 
Power Essential 

A big part of making the first complete 
small computer is providing you with a wide 
range of easy to use, easy to obtain, low cost 
software. For the Sol-20, we've developed a 
whole group of offerings. And more are on 
their way. 

Sol Systems Price List 



(prices are net, effective Dec. 1, 1976) 








SOFTWARE 












CUTS 


Paper 


ITEM with manual 


Source 


cassette 


tape 


BASIC 5 software 








#2 


yes 


** 


$19.50 


8K BASIC 


no 


$29.00 


$37.00 


New 8080 Focal 


no 


$14.50 


N/A 


TREK 80 video 








game 


no 


$ 9.50 


$14.50 


GAAAEPAC 1 








video games 


no 


$ 9.50 


$14.50 


AAATHPACK video 








calculator 


yes 


$14.50 


$19.50 


ASSEMBLER 








software #1 


yes 


$14.50 


$19.50 



**CUTS cassette of BASIC 5 is included FREE with all orders for Sol 
units or CUTS cassette interfaces. Additional cassettes available 
for $14.50. 

Sol system owners be sure to note Sol 
system on your order. These special versions 
use less code and provide easier loading 
along with more convenient operation. 
SOLOS, SOLED and CONSOL all have provi- 
sion for the special versions. 

All Processor Tech no logy software is 
distributed on an individual sale basis for 
personal use. No license to copy, duplicate 
or sell is granted with this sale. Each software 
package has been copyrighted by Processor 
Technology and all rights therein are reserved. 

Sol Terminal Computers Kit Price 

SOL-PC SINGLE BOARD TERMINAL 

COMPUTER™ $475.* 



SOL-10 TERMINAL COMPUTER™ 
Sol-PC with case, power supply 
and 70 key solid state keyboard. $795. 

SOL-20 TERMINAL COMPUTER™ 
all features of Sol-10 with larger 
power supply, 85 key solid state 
keyboard, fan, and five slot 
expansion backplane. $995. 

*Sol prices include CONSOL 
Personality Module. If SOLED Intelligent 
Editing Terminal Module or SOLOS Stand- 
alone Operating System Module is desired 
instead, add $100. If ordered separately, 
personality modules are $150 each. 

Mass Storage Systems 

Helios II Disk System™ 
includes dual PerSci 270 
floppy disk drive, cab- 
inet, fan,S-100 buscompatible 
controller, power supply, sys- 
tem diskette with complete 



PTDOS software 

Memory Modules 

ALS-8 PROM Resident Assembly 

Language Operating System 
SIM-1 Interpretive Simulator 

add-on option for ALS-8 
TXT-2 Text Editing add-on 

option for ALS-8 
2KRO Erasable PROM module 
4KRA 4096-word Low Power 

Static RAM 
8KRA 8192-word Low Power 

Static RAM 
16KRA 16384-word Dynamic 

RAM 

Interface modules 

3P+S Parallel/Serial I/O 

module 
CUTS Computer Users Tape 

System cassette interface 
VDM-1 Video Display Module 



$1895 $2295 

Kit Asmbld. 

— $425 

— $ 95 

— $ 95 
$ 65 $ 89 

$159 $195 

$295 $375 

— $529 

$149 $199 

$ 87 $119 
$199 $295 



See your nearest dealer or contact us directly. 
Address Processor Technology, 
6200B Hollis Street, Emeryville CA 94608, 
Phone 415/652-8080. 




Give 

Your 

Micro 

Some 

Muscles 






Robert D Grappel 
148 Wood St 
Lexington MA 02173 



A lot of proposed microcomputer appli- 
cations require the computer to control 
various mechanical devices. Opening and 
closing valves, moving things, pushing, 
turning, etc, are not things that computers 
can do without help. This article describes a 
surprisingly easy way to turn digital signals 
into mechanical motion. This will make it 
easier to design plotters, controllers . . . 
anything that requires motion. 

Before I was bitten by the "computer 
bug," my hobby was building radio con- 
trolled aircraft. In trying to solve the prob- 
lem of transferring the position of the pilot's 
hand to the position of a control surface on 
the aircraft, we modelers gradually came to 
use digital systems. The servomechanisms 
used in aircraft are very sophisticated 
devices. They are tiny, less than 3 cubic 
inches (49 cubic centimeters). They are 
light, less than 2 ounces (58 grams). They 
provide up to 4 pounds (1 .8 kilograms) of 
thrust. Each servo requires less than 200 mA 
of current at 5 V. They continue to work 
over a wide temperature range and in condi- 
tions of extreme vibration. It seems to me 
that such devices would make ideal muscles 
for our computers. Servos are readily avail- 
able, and are relatively cheap at around $25 
to $50. How does one interface an aircraft 
servo to a micro.? Would you believe three 
connections? Yes, it really is that simple. 

You will want to use what is called a 



See Sol now 

The full line of Processor Technology 
Sol Computers, systems, software and 
peripheral equipment is on display 
now at your nearby Sol store 



CALIFORNIA 
1514 University Ave. 
Berkeley CA 94703 
The Byte Shop 
2559 South Bascom Ave. 
Campbell CA 95008 
Byte Shop Computer 
Store 

6041 Greenback Lane 
Citrus Heights CA 95610 
The Byte Shop 
16508 Hawthorne Blvd. 
Lawndale CA 90260 
The Byte Shop 
1063 El Camino Real 
Mountain View CA 94040 
The Computer Mart 
624 West Katella #10 
Orange CA 92667 
The Byte Shop 
2227 El Camino Real 
Palo Alto CA 94306 
The Computer Store 
of San Francisco 
1093 Mission Street 
San Francisco CA 94103 

The Byte Shop 
155 Blossom Hill Rd. 
San Jose, CA 95123 
The Byte Shop 
509 Francisco Blvd. 
San Rafael CA 94901 

The Byte Shop 
3400 ErCamino Real 
Santa Clara CA 95051 
The Byte Shop 
2989 North Main St. 
Walnut Creek CA 94596 

FLORIDA 

Microcomputer 

Systems, Inc. 

144 So. Dale Mabry Hy. 

Tampa FL 33609 

GEORGIA 

Atlanta Computer Mart 
5091-B Buford Hwy. 
Atlanta GA 30340 

ILLINOIS 

The Numbers Racket 
518 East Green Street 
Champaign IL 61820 
itty bitty 

machine co., inc. 
1316 Chicago Ave. 
Evanston IL 60201 



INDIANA 

The Data Domain 
406 So. College Ave. 
Bloomington IN 47401 

KANSAS 

The Computer Hut 
521 N. Hillside 
Wichita, KS 67214 

MICHIGAN 

The Computer Store 

of Ann Arbor 

310 East Washington 

Ann Arbor Ml 48104 

General Computer Store 

2011 Livernois 

Troy Ml 48084 

NEW JERSEY 
The Computer Mart 
of New Jersey 
501 Route 27 
Iselin NJ 08830 
Hoboken Computer Works 
No. 20 Hudson Place 
Hoboken NJ 07030 

NEW YORK 

Audio Design Electronics 
487 Broadway, Ste. 512 
New York NY 10013 
The Computer Corner 
200 Hamilton Ave. 
White Plains NY 10601 
The Computer Mart 
of Long Island 
2072 Front Street 
East Meadow, L.I. NY 
11554 

The Computer Mart 
of New York 
314 Fifth Ave. 
New York NY 10001 
Synchro Sound 
Enterprises 
193-25 Jamaica Ave. 
Hollis NY 11423 

OREGON 

The Real Oregon 

Computer Co. 

205 West 10th Ave. 

Eugene OR 97401 

Byte Shop Computer 

Store 

2033 S.W. 4th Ave. 

Portland OR 97201 



OKUHOMA 
High Technology 
1020 West Wilshire Blvd. 
Oklahoma City OK 73116 

RHODE ISLAND 
Computer Power, Inc. 
M24 Airport Mall 
1800 Post Road 
Wan/vick Rl 02886 

TEXAS 

The Micro Store 

634 South Central 

Expressway 

Richardson TX 75080 

WASHINGTON 

The Retail Computer 

Store 

410 N.E. 72nd 

Seattle, WA 98115 

WASHINGTON, D.C. area 
Media Reactions Inc. 
11303 South Shore Dr. 
Reston VA 22090 

WISCONSIN 
The Milwaukee 
Computer Store 
6916 W North Ave. 
Milwaukee Wl 53213 

CANADA 

The Computer Place 
186 Queen St. West 
Toronto, Ontario M5V 1Z1 
Trintronics 
160 Elgin St. 
Place Bell Canada 
Ottawa, Ontario K2P2C4 
First Canadian 
Computer Store Ltd. 
44 Eglinton Ave. West 
Toronto, Ontario M4R 1A1 
Pacific Computer Store 
4509-11 Rupert St. 
Vancouver, B.C. V5R 2J4 










+ 5V 



I 



!6-20mS 



ImS 
(MINIMUM) 



JTL 



UP TO ImS 
(MAXIMUM) 



Figure 1: Timing diagram of the waveform that is needed to drive the 
servomechanism. The pulses are from 16 to 20 ms apart in time, and have a 
pulse width of 1 to 2 ms. This type of timing can be accomplished using your 
computer's internal clock as a reference in timing loops, or through a 
programmable real time clock. 



three wire servo which is the modern type 
unit. These run on regulated 5 V supplies. 
That takes care of two of the necessary 
connections. The third lead is the input 
signal. This is a TTL compatible signal, 
which can be driven from one bit of a 
typical output port. We will use software to 
generate the proper waveform at this bit. 
Since each servo requires only one output 
bit, a typical byte port can drive up to 8 
servos. 

Servos are really pulse width feedback 



LUCN 


81 


82 


B2 










2001 








> 




ORG S2001 




2001 








>* 


PROGRAM TO TEST 


MUDEL AIRPLANE SERVO 


2001 








>* 




WRITTEN BY OARL HELMERS 12/B/76 


2001 








>* 




ASSEMBLED wl TH uACn EMMEHICHS* ASSEMBLER 


2001 








>* 




ILLUSTRATION 


hOH HUBER1 GHAPPEL'S AR1I0LE 


2001 








>* 








2001 
0151 








>* -- 
>PIAC 


EQU A 151 


- - - - - L>A 1 A DEfr I N I i' I OftS -------------------- 

PI A CGNTHuL REGISTER ADDRESS 


0150 








>PIAb 


EQU SI 50 


PIA DATA/ 01 RECTI UN KEGISTER ADDRESS 


01 38 








>MIL1 


EQU £138 


MI LI (8) MILLISECOND DELAf ROUTINE 


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00 


00 




>DATA 


KDB 


SERVO POSITION DATA REGISTER 


014F 








»LAMZ 


EQU S14r 


LAMPS 


2003 








>* 








2003 








>* 






-------- PRO GRAM- ------------------------- 


2O03 








>* 


MAIN ENTRY POINT 


2003 


7F 


01 


51 


>ENTY 


OLR P1A0 


SET UP THE PIA 


2006 


7J- 


01 


50 


> 




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WITH ALL LATA 


2009 


73 


01 


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> 




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BITS OUTPUT 


2O0C 


86 


04 




> 




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B7 


01 


51 


> 




STAA PIAO 




2011 


If 


01 


50 


> 




OLR PIAD 


POSITIVE GOING PUL^E SETUP 


2014 








>* 








2014 








>* 


MAIN EXECUTION 


LuOP 


2014 








>* 








2014 








>* 


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2014 


73 


01 


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START PULSE 


2017 


C6 


01 




> 




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2019 


BU 


01 


3H 


> 




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2010 


86 


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> 




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> 




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> 




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2027 


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> 




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> 




END 




*** END 


- UNRESOLVED ITEMS* 




*♦* SYMBOLS t 










DATA 


2001 


ENTY 2003 LAMZ 014F 


MILI 0138 PIAO 0151 


PIAD 


0150 


PUL1 20 IK PULS 2014 


§ 




Notes on Trying Robert's Idea for Muscles 
by Carl Helmers, editor 

Using the servo we bought to take the 
picture of photo I, I wrote the program 
shown in this listing to illustrate the opera- 
tion and test out the characteristics of the 
device. The program is written for my 
homebrew 6800 system, which has parallel 
interface ports at hexadecimal addresses J 50 
to 157 in memory address space. The PIA 
port at locations 150 and 151 was used for 
this experiment, with some binary indicator 
lamps at location 14F used to tell what the 
current state of the command parameter 
was. This program uses a subroutine in my 
monitor called MILI which is a timing loop 
returning to the calling point 1 millisecond 
after entry. The interpulse space was 
arbitrarily set at 250 ms (it worked) in order 
to allow observation of what was happening 

Continued on page 34 

Photo 1: A typical model aircraft servo, 
which we purchased at a local hobby shop in 
Greenville NH. The price of this unit was 
about $45, and the only documentation we 
could find on it, the catalog, said it could 
exert 5 pounds of force, presumably at the 
limit of the lever arm provided by the 
standard bell cranks and connection wheels 
which came with it. We took it apart after 
photography and found a gearbox with 
several gears, the motor, potentiometer 
slaved to the main output shaft, and electron- 
ics. Although the printed circuit board 
internal to the device had ''made in Japan" 
marked on it, the actual integrated circuit 
was clearly a result of international trade — 
It was marked "Texas Instruments." After 
reassembly, it was tried out with the pro- 
gram shown in the box accompanying this 
article, using a PIA port at address location 
0150 (hexadecimal). 



units. The input is a pulse with a carefully 
controlled width. The servo contains an 
electric motor, a gear train, a feedback 
potentiometer connected to the gearing, and 
some fairly sophisticated electronics. In 
modern servos, all the electronics is con- 
tained in a custom integrated circuit. The 
circuit generates an internal pulse every time 
it receives an input pulse. The internal pulse 
width is controlled by the feedback pot. The 
circuit then compares the pulse widths. If 
they match, then no current goes to the 
motor. If they do not match, then current is 
fed to the motor and it drives the mechanics, 
together with the feedback pot, in the 
appropriate direction until the pulse widths 
again match. By feeding pulses in a rapid 
stream into the servo, it will appear to track 
the varying pulse width. 

Just about every servo sold for use in 
model aircraft expects pulse widths varying 
between 1 and 2 ms. Most servos use positive 
going pulses, but there are a few servos 
around which require negative going pulses. 
The pulses should be repeated every 16 to 
20 ms. The repetition frequency is not criti- 
cal. The servo will run from extreme to 
extreme in about 0.5 s. To drive the servo, 
one then needs to generate a waveform like 
that in f igure 1 . This can be done with 
timing loops, interrupts or programmable 
timers. Even the slowest processor can 
handle this task. 

Model boats, and some aircraft, use elec- 
tric power plants. The same type of controls 
can be used to vary the speed and direction 
of electric motors. For readers interested in 
controlling motors, and other high power 
devices, I would recommend the circuits 
published in RCM, (Radio Control Modeler). 
Page 166 in the April 1976 issue shows a 
circuit using the integrated circuit from a 
servo and two external transistors to control 
a 20 A motor from full stop to full speed. 
Page 12 of the September 1976 issue shows 
a similar circuit which has the added feature 
of forward and reverse control. Circuits like 
these can also control other loads, like lights 
or heaters. This is fully proportional control, 
not just on and off. 

Now there is no excuse for not building 
that robot you were thinking about. You 
can use servos to control your tape cassettes 
by pushing the buttons under computer 
control. Using two servos, one in the X 
direction and another in the Y direction, a 
pen plotter can give your computer a hard 
copy graphics capability. There are hundreds 
of exciting possibilities. I hope to read of 
some of them in these pages soon." 



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The brand new SB-1 Music Board can generate 
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sustain reside in hardware, not software. Since you 
can store several waveforms in memory, your 
computer will play more than one instrument. The 
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the SB-1 allows you to easily input the notes just as 
you would read them and adjust the sounds by 
controlling the waveform. The output of the SB-1 
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output, or approximately 1 volt RMS with accuracy 
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PAPERBYTES™ Forum 



Machine readable printed software is an exciting subject. Numerous 
comments have been received from various individuals regarding the idea of 
machine readable printed software as described in the November and 
December 1976 issues of BYTE. These are excerpts from various letters 
which often covered other topics as well: 



Multiple Synch Characters . . . 

Several people have suggested that 
the format should contain multiple SYN 
characters. Here are a couple of 
examples of the comments: 

I have a few comments on the pro- 
posed standard for machine readable 
printed data. (My forte is not building 
bar code readers, but I do have some 
experience in high speed data trans- 
mission.) In the proposed frame layout I 
would suggest duplicating the SYNCH 
character at least one more time, and 
possibly a couple more times. The rea- 
soning is that even if the timing marks 
are included (which I don't think were in 
the December samples) the adaptive 
algorithm must establish "bit synch" to 
extract the bits correctly, and then it 
must establish "character synch" to 
insure it has gotten the character bound- 
aries correct. In data transmission 
schemes, usually two or four synchs are 
used depending on whether the synch 
pattern is to establish only character 
synch or both character and bit synch. 
The modulation schemes you have pre- 
sented seem to have enough transitions 
in them to get bit synch, so four synchs 
probably aren't needed. But the algo- 
rithm would be a lot more sure of what 
is going on if there were at least two 
synchs: one to get synched, and one to 
check the synch. I think this is particu- 
larly important considering the data 
following the synch is the checksum. 
Slop or jitter from the startup of the 
human hand could be particularly dam- 
aging here. A few extra synchs thrown in 
could solve that potential problem. 

Maybe I am trying to make this all 
too complicated, but my background is 
one of insuring robustness in protocols. 
The bar code wand reader experts prob- 
ably have a better feeling than I for 
things like this. 

Mike O'Dell 

University of Oklahoma 

Information and Computing Sciences 

601 Elm, Rm 926 

Norman OK 73069 



Another reader suggested putting a 
second SYN character at the end of the 
frame in order to allow scanning in 
either direction, a sentiment which was 
echoed by Tom Pittman of Tiny BASIC 
fame. But using the sparse format shown 
in the examples in this issue [or for- 
mat (c) of December BYTE, page 17], 
the frame capacity is only about 26 to 

13 



32 data bytes, depending on length, so a 
3 to 4% penalty in capacity is required. 
Also, the main advantage is to allow 
sweeps in both directions, which for 
manual scanning may not be particularly 
important since the rhythm of operation 
has to be interrupted by repositioning 
the guide straightedge between each 
swipe. 

Printed, Machine Readable Braille? 

Totally unrelated to our bar code 
representation for data, but nevertheless 
interesting, is this letter from C R 
Conkling jr, and his accompanying 
sample. 




The sample is a short segment of the 
text, reproduced here twice the original 
size, which was a test occupying two 
sides of a letter size sheet of enameled 
paper. 

I was interested in your thoughts on 
using ink print to transmit digital infor- 
mation. I have enclosed an ink printed 
sheet of paper which was printed using 
standard offset methods. The paper con- 
tains a complete pocket paperback size 
book. I must say, however, that it is in 
grade 2 Braille which uses contractions, 
as in speed writing. The Braille code is a 
6 bit code, and the paper is encoded to 
drive a mechanical Braille cell to repro- 
duce the data. 

Why it was done is a long story. Why 
it was never completed is even longer. 
One of the reasons that it was never 
completed was that we had no luck 



Continued on page 82 









Editorial 



BYTE Goes International 



by Carl Helmers 



Accompanying this editorial is a letter 
from an Australian reader, Kevin C Barnes of 
Five Dock, New South Wales. He's writing 
on the conditions of the small computer 
person in Australia circa September 1976. 
We held onto the letter until it was possible 
to announce an arrangement which should 
help promote and build an indigenous small 
computer industry in Australia: the new Far 
East Asian editions of BYTE magazine. 

When BYTE first began circulation, an 



electronics engineering consultant named 
John Bannister, a native of Sydney, Aus- 
tralia, subscribed nearly instantaneously 
when he heard about it from an American 
friend. But he soon ran into a problem 
which plagues all individuals on the end of a 
long international supply chain — it takes 
time and patience to await BYTE (or any US 
goods, for that matter) in Australia, which is 

Continued on page 62 



Are Logic States Inverted Down Under? 

Here are just a few notes that might 
be of interest to your readers about 
conditions in Australia. Interest in com- 
puting is just about to happen down 
here. Both national electronics maga- 
zines, Electronics Australia and Elec- 
tronics Today International have just 
(July 1976 issue) started to talk about 
microprocessors. They have started by 
reviewing the different evaluation boards 
available. But neither magazine has pub- 
lished any construction articles as yet on 
microprocessor based microcomputers. 
[EA did design and publish an 8 bit 
processor back in the end of 1974 and 
beginning of 1975, but it was a serial 
processor which did not gain the popu- 
larity of the present microprocessor 
systems. That processor, the EDUC-8, 
was built using TTL MSI and SSI chips 
and had a limited memory of 256 
locations. In fact EA was beaten to the 
honor of being the first to publish a 
computer plan by only a few weeks by 
Radio Electronics' publication of the 
Mark 8.) 

Commercial interests now have a 
number of American designed and built 
systems offered for sale, but unfortu- 
nately these people do not yet carry 
much stock. MITS equipment is offered 
down here by a company called WHK of 
Melbourne, and the proprietor has pub- 
lished a rather impressive catalog with all 
the MITS hardware and software listed. 
JOLT is also being advertised as well, 
although mainly through the trade jour- 
nals. EPA's Micro 68 also has been 
offered for sale and the agent has at least 
one in stock which he is willing to lend 
to people to look at and play with. 

I and three other people have formed 
a small club and have three systems 
operating, using the 6800, 8080 and the 
SC/MP chips. They have been built 
around evaluation boards. We also have 
an ASR-33 and ASR-38 Teletype and 



our big project at the moment is a 
floppy disk. Our small project of the 
moment is a PROM programmer to 
program 1702s. In my conversations 
with various integrated circuit manufac- 
turing company representatives, I've 
gained information that a good propor- 
tion of the sales here have been to 
individuals, not companies, and that 
many boards bought by companies have 
been for individuals within the com- 
panies and not for particular company 
projects [standard practice in the US, 
too . . .CH). 

Also very annoying is the rather high 
price markup on the hardware by the 
time it reaches Australia. The Intel 8080 
Microprocessor System User's Manual 
for instance has sold for $20 even 
though it is marked $5, while the Altair 
8800A sells for $619 Australian ($740 
US currently) for the basic kit with no 
extra boards. Well, I hope this has been 
of interest. 

Kevin C Barnes 

71 Barnstaple Rd 

Five Dock 

New South Wales 2046 

AUSTRALIA 

Thanks for your comments, Kevin. 
By the time this letter is in print, it will 
be part of the third issue of our new 
Australian English language edition of 
B YTE, so with any luck you 'II soon start 
to find some increases in personal com- 
puting activity in your vicinity. Until 
there is local manufacture, there is no 
way you can beat the price penalty, as 
nearly as I can project: Shipping costs 
time and money. When a product is dear, 
whether through distance or natural scar- 
city, Adam Smith and Co long ago pre- 
dicted the price would rise. I understand 
from John Bannister, however, that at 
least you don't have to pay an exorbi- 
tant import tariff as our Canadian 
friends do. 



14 



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Letters 



8080 TRICKS AND FAST OPTICS 
FOR ISOLATION 

In the November 1976 letters col- 
umn, reader Bennett asked for an easy 
way to do an arithmetic shift right using 
the 8080. Try RLC, RAR, RAR; only 
three bytes, and the carry bit ends up 
thesame as with SRA A on the Z80. 

By the way, if anyone wants to try 
an optically coupled video interface to a 
television, look at HP's 5082-4360 op- 
tically coupled logic gate. It's rated for 
10,000 bits per second and costs 
$6.30 in unit quantity. Cheaper optical 
couplers can handle sync and, if neces- 
sary, an on/off control, but the HP 
device is the first one I've seen that looks 
fast enough to handle video frequencies. 
Using a separate device for sync avoids 
critical biasing adjustments to make a 
single device operate in the linear mode. 
With separate devices, the video and sync 
mixer goes on the output side of the 
devices. Frequency response can go 
down to DC if you can avoid upsetting 
the television's video stage bias without 
using a DC blocking capacitor. 

Robert F Miles 

242 Abingdon Rd NW 

Lenoir NC 28645 

OOPS ...SUPPLIES GONE 

After reading the "An Item of Inter- 
est" article in the September issue of 
BYTE (page 100), I wrote to SWTPC for 
the June 1976 newsletter. But the news- 
letter is not in print anymore. 

Is there any way I could get a used 
or old June 1976 newsletter? Please 
respond. 

Robert Leong 

705 N Linden Dr 

Beverly Hills CA 90210 

WANTED: ELIZA FOR THE 
SMALL COMPUTER 

Many years ago I had a dialog (my 
first online experience!) with a computer 
that conversed like a psychiatrist, select- 
ing phrases from my input and feeding 
them back in new context or, if nothing 
good suggested itself, injecting a random 
phrase such as "how did you feel about 
your father?". It was called the ELIZA 
program, because it learned from its 
input. According to one article I have 
read, it was originated at MIT. 

Now, after considerable timesharing, 
I am a subscriber to BYTE and am 
buying an Altair 8800a on the Kit-a- 
Month plan. Is anyone in BYTEIand 
familiar with the software for ELIZA? In 
particular, does anyone know of a ver- 



sion suitable for small machines? I'll try 
to reinvent it if I must, but it seems silly 
to do so. 

John P Aurelius 

2568 10th Av W 

Seattle WA 98119 

ELIZA is a program created by 
Joseph Weizenbaum at Massachusetts In- 
stitute of Technology, which has since 
spread somewhat widely - in ways not 
necessarily consistent with its creator's 
goals. See BYTE's review of Weizen- 
baum 's book, Computer Power and 
Human Reason, on page II, January 
1977. The book is highly recommended 
reading for any intellectual. As to 
whether detail implementations of 
ELIZA style programs can be found, 
maybe a reader with academic connec- 
tions can enligh ten us. 

THAT'S THE RIGHT IDEA . . . 

I'd like to give my support to Charles 
Wortell's entry to the Programming 
Quickies column [December 1976, page 
132]. A few months ago I thought of 
presetting memory of my 6800 system 
to SWI (hexadecimal 3F) to catch way- 
ward programs. I'd like to suggest the 
following to anyone considering a ROM 
operating system for a 6800: I've re- 
placed the MIKBUG monitor in my 
SWTPC 6800 with a PROM monitor that 
initializes memory to SWI. This is only 
done on power up reset and not on 
subsequent resets. 

I've changed all interrupt vectors to 
addresses in the processor board RAM. 
This allows faster interrupt service and 
frees the SWI for alternate uses. As an 
added bonus an unexpected interrupt 
from 10 will cause a register print just 
like SWI. 

I'd welcome correspondence from 
readers considering this and other rou- 
tines I included in my monitor. 

Leo Taylor 

18 RidgeCt W, Apt 21C 

West Haven CT 06516 

You've got the right idea with respect 
to customizing and extending monitors. 
I've done a similar thing in my own 
machine by writing a monitor program 
much more capable than MIKBUG. 
How'd you like to start a 6800 systems 
programming special interest 
group? , . . CH 

ALTAIR WORD 
PROCESSING NEEDED 

I am interested in using my Altair 
8800 to produce clean letters and re- 
ports from text entered through a key- 
board with editing capabilities. Is there 
anyone out there who has an Altair 
compatible software package who can 
help me? 

Also I'd like to inform you that we 
have formed a Stony Brook Homebrew 
Computer Club, which is both hardware 
and software oriented. We have friendly 



and informal meetings and access to 
various simulators and cross-assemblers 
on the school computer. Members have 
their own systems to demonstrate and -^\^ 
discuss (8080 and 6800). 

Ludwig Braun 

Professor of Engineering 

State University of NY at Stony Brook 

Stony Brook NY 11794 

Text editing is one area where we 
expect to use our office Altair, among 
other things. Try writing in 6 months or 
a year if you haven't found a source by 
then. 

YE OLDE BOARD 
SWITCHE MANOEUVRE 

The following is a simple fix I found 
for a crashing Altair 8800. The symptom 
was apparent false jumps when loading 
and operating 1 2 K BASIC for a few 
minutes. These errors wiped out parts of 
the loaded software, outputting "syn- 
tax" errors, garbage or nothing. The fix 
was to move the processor card to the 
center of the case (near the fan), away 
from other boards, and to tape (double 
back sticky) an aluminum foil (~1 X 2 
inch) heat sink (convection cooled) onto 
the SN74123. No problems have oc- 
curred since. 

Dr F R Ruckdeschel 

Principal Scientist 

Xerox Corp 

PCDD/P&MS/EDPA ^ 

800 Phillips Rd 1 

Bldg 129 

Webster NY 14580 

WANTED- 6502 USERS 

I would like to say that I enjoy your 
magazine very much, and look forward 
to it every month. It always seems to 
have the articles I am looking for, and 
they are always entertaining. 

I am presently bringing up a 6502 on 
an OSI superboard and am interested in 
speaking to anyone with a micro, espe- 
cially a 650x series computer. If anyone 
has a monitor that they think is really 
great, or at least perfect, please give me a 
call or drop me a line. My phone number 
is (613) 692-3786. Ask for Kevin. 

Kevin Szabo 

Box 86, Hillcrest Dr 

RR 1, Manotick, Ontario 

CANADA K0A2N0 

PAGING WITH AN 1802 

First of all, thanks for coming up 
with a computer magazine for the ex- 
perimenter just when I needed it. 

In regards to the editorial "The Ad- 
dress Space Saturation Problem" by Carl 
Helmers in your November 1976 issue, 
page 16, I would like to make a sugges-^^^ 
tion. The RCA Cosmac 1802 micro- / 
processor, which was used in the recent 



Continued on page 94 



16 




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• Character set and pitch variable under software 
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•5x7 character matrix 

• Ribbon has built-in re-inkers for a life of 
10,000,000 characters 

• Paper can be either a standard 8V2-inch roll, fanfold 
or cut page 

• Interfaces to 8-bit parallel ports 



There are lots of capabilities and outstanding features of the 
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A Review of 



Photo 1: The PR-40 dot 
matrix printer as assem- 
bled from the kit dis- 
tributed by Southwest 
Technical Products. The 
printer is not enclosed in a 
case but is mounted on a 
black anodized aluminum 
chassis with overall dimen- 
sions of 9.63 by 10.50 by 
8. 75 inches (24.45 cm by 
26.67 cm by 22.23 cm). 



the SWTPC PR-40 Alphanumeric Printer 



Gary Kay 

Southwest Technical Products Corp 

219 W Rhapsody 

San Antonio TX 78216 






Ever since the microprocessor's introduc- 
tion, computer hobbyists everywhere have 
been searching for a low cost alphanumeric 
printer. One place the search can stop is at 
the unit presented here: a 5 by 7 dot matrix 
impact printer. It prints the 64 character 
upper case ASCII set with 40 characters per 
line at a rate of 75 lines per minute on 
standard 3.875 inch (9.843 cm) rolls of 
adding machine paper, as shown in figure 1. 
One complete line is printed at a time from 
an internal 40 character first in first out 
buffer memory. Printing takes place either 
on receipt of a carriage return -or automati- 
cally whenever the line buffer memory is 
filled. 

The printer can accept character data as 
fast as one character per microsecond (until 



the buffer is full) or as slow as you wish to 
send it. The printer's seven parallel data lines 
are TTL compatible and may be enabled by 
a single data ready control line or by 
separate data ready and data accepted hand- 
shake control lines. This universal approach 
makes the printer compatible with all com- 
puter and terminal systems having an eight 
bit parallel interface port; including, of 
course, the SWTPC 6800 and MITS Altair 
8800 computer systems. 

The printer mechanism is attached to a 
black anodized aluminum chassis with front 
trim panel which houses the circuitry includ- 
ing its own 120 or 240 VAC 50 to 60 Hz 
power supply circuit shown in figure 2, 
making the printer's overall dimensions 
9.625 by 10.50 by 8.75 inches (24.45 by 
26.67 by 22.23 cm). 

The' Mechanics 

The entire design, shown in photo 2, is 
based on a simple and reliable print mecha- 
nism intended originally for point of sale 



18 



- 



Figure 1 : Example print- 
out demonstrating the 
type of characters that are 
generated by the PR-40 
dot matrix printer. The 
printout is the width of 
readily available 3.875 
inch (9.843 cm) adding 
machine paper. The test 
program of listing 1 gen- 
erated this printout. 



1 "MJJ&'O' 
GfiBCDEFGHI 

! "#*;•;&■'<)+ 

efiBCDEFGHI 

! "wj&'o* 

ipfiBCC'EFGHI 
! "tr/Ji'O* 
eflBCDEFGHI 
! "•*;&'<>* 
GflBCDEFGHI 
1 "#«&'()+ 
C-flBCDEFGH 
! "MXA'O* 
GfiBCC-EFGHI 
1 "Mi&'O' 
C-flBCDEFGH 

! "«;;&"(> 

SflBCDEFGHI 



0121456789: ; <=>? 
JKLMNOPGRSTUVWXVZ C \ ] t 

/Bl23:456789: ; <=>? 
JKLMNOPQRSTUVWXVZC \] t 
+, -. /6123456789: ; <=>? 
JKLMNQPQRSTUVMXVZC\3t 
+, - /0123:456789: J 0>? 
JKUWOPQRSTUVHWZC'Ot 
+, - /0123:45S7S9:;C=>? 
JKLMN0P6RSTUVWXVZ C \] t 

/6123:45t:7£:9: i 0>? 
JKLMNOPQRSTUVWXVZCXlt 

/0123:456789: ; <»? 
JKLMNOPQRSTUVIJXVZCSJt 
+j -. /01 23456789: ; <=>? 
JKLMNOPGRSTU VWXYZ C \ ] t 
+,-. /EH2J45c;78y :;<»? 
JKLMNOPQRSTUVMXVZC\]t 



terminal use. The printed characters are 
formed by moving the print head horizon- 
tally across the paper while selectively ener- 
gizing solenoid driven print wires on the 
head which strike an inked ribbon and 
imprint dots on standard adding machine 
paper. All seven of these solenoid driven 
print wires converge at the tip of the print 
head in a vertical line which is perpendicular 
to the horizontal direction of movement of 



=c^ 



Fl 

2.5A 

SLO-BLO 






the print head. By selectively firing the print 
wires, 5 dot wide by 7 dot high characters 
are printed as the print head moves across 
the paper. A one dot time spacing is left for 
separation between the printed characters. 
This method of printing characters is not 
new but the method of moving this wire 
impact print head is unique. Rather than 
using dual motors, clutches, timing bars and 
the other hardware usually associated with 



SIB 

DPST J>6 

o^o O- \^> +40VDC 




{^> GND 2 



\ ^> +BVDC 



£3> -I2VDC 
^> GND I 



^— , MOTOR 
<s I CONTROL 



Figure 2: The schematic 
diagram of the power sup- 
ply circuit for the PR-40 
printer. Th is power supply 
can be run on either J 20 
or 240 VAC depending on 
whether the primary wind- 
ing is wired in parallel or 
series. The power trans- 
former, 77, has a J 20, or 
240 V primary; 32 V 
@2 A, 12.5 V @1 A center 
tapped, 120 V @200 mA 
center tapped secondaries. 
As can be seen in the 
diagram, the printer motor 
is triac controlled, taking 
its on and off states from 
the position of the printer 
head on the page. All re- 
sistors are measured in 
ohms and are 0.25 W un- 
less otherwise stated. 



19 



A Printer Testing Program 

The printer diagnostic program of 
listing 1 has been written to test and 
debug the SWTPC PR-40 printer when it 
has been interfaced to the SWTPC 6800 
computer system through one of the MP 
L parallel interface boards. It is assumed 
that before loading this program, the rest 
of the system is functioning normally 
with no problems. The program itself 
uses 60 words and is loaded within the 
128 word programmable memory used 
by the MIKBUG® operating system on 
the MP A microprocessor and system 
board. A program may reside in external 
programmable memory simultaneously 
with the diagnostic loaded within the 
128 word programmable memory, or the 
diagnostic may be run with no MP M 
memory boards installed on the system 
at all. The diagnostic may be loaded 
either from tape or instruction by in- 
struction using MIKBUG starting from 
hexadecimal address A014 through 
A024 and then from hexadecimal ad- 
dress A048 through A072. The address 
of the MP L parallel interface board 
feeding the printer must be set using 
MIKBUG to load the hexadecimal ad- 
dress of the selected port into hexadeci- 



mal memory locations A002 and A003 
with the most significant byte going into 
A002 and the least significant byte going 
into A003. The starting address locations 
of the interface ports are given in table 
1. 

Since the program counter is set when 
the program is initially loaded, the diag- 
nostic is initiated as described in the "go 
to user's program" section of Engineer- 
ing Note 100. Once initiated, the pro- 
gram can be stopped only by depressing 
the reset button. The program may then 
be restarted after resetting the program 
counter to hexadecimal A04A as de- 
scribed in the "display contents of proc- 
essor registers function" section of Engi- 
neering Note 100. 

The diagnostic works by sending out 
an ASCII carriage return, hexadecimal 
OD, followed by hexadecimal ASCII 
characters 21 through 3F followed by 
another carriage return 0D, followed by 
hexadecimal ASCII characters 40 
through 5E inclusive, repeating itself 
until stopped with the reset switch. 

Each character is output to the 
printer by first storing the ASCII char- 
acter's bits through 6 on output lines 
00 through 06 of the selected MP L 



Listing 1: A debug and test program written for a 6800 type system with 
MIKBUG. The hexadecimal address of the selected port is loaded into 
memory locations A 002 and A 003 which are referred to by PARA DR. The 
program counter is initiated at the beginning of the program. The program 
sends out a carriage return, hexadecimal ASCII characters 21 through 3F 
followed by a carriage return, followed by hexadecimal ASCII characters 40 
through 5E, and repeated indefinitely. 



Address 


Op 


Operand 


Label 


Mnemonic 


Commentary 


A014 


A7 


00 


OUTCHR 


STA A0,X 


PARADR: = A; 


A016 


C6 


37 




LDA B #37 


) PARADR+1:=37; 
J [data ready port] 


A018 


E7 


01 


1 


STAB 1,X 


A01A 


C6 


3F 




LDA B #3F 


) PARADR+1:=3F; 
J [data ready port] 


A01C 


E7 


01 




STAB 1,X 


A01E 


6D 


01 


LOOP3 


TST 1 ,X 


check if data accepted signal 
received; 


A020 


2A 


FC 




BPL LOOP3 


if signal not present go to 
LOOP3; 


A022 


E6 


00 




LDA B 0,X 


else B:= PARADR 


A024 


39 






RTS 


return; 


A048 
A049 


A0 
4A 






MSB 
LSB 


[ [program counter] 


A04A 


FE 


A0 02 


START 


LDX PARADR 


X:= PARADR; [IO port 
address] 


A04D 
A04F 


C6 
E7 


FF 
00 




LDA B #FF 
STA B 0,X 


\ PARADR: = FF; 


A051 
A053 


C6 
E7 


3F 
01 




LDA B #3F 
STA B 1 ,X 


| PARADR+1: = 3F; 


A055 


86 


0D 


FSTLIN 


LDA A #0D 


} output carriage return; 


A057 


8D 


BB 




BSR OUTCHR 


A059 


86 


20 




LDA A #20 


A:=20; 


A05B 


4C 




LOOP1 


INC A 


A:=A+1; 


A05C 


81 


40 




CMP A #40 


compare A to 40; 


A05E 


27 


04 




BEQ NXTLIN 


if A=40go to NXTLIN; 


A060 


8D 


B2 




BSR OUTCHR 


go to OUTCHR; 


A062 


20 


F7 




BRA LOOP1 


goto LOOP1; 


A064 


86 


0D 


NXTLIN 


LDA A =0D 


> output carriage return; 


A066 


8D 


AC 




BSR OUTCHR 


A068 


86 


3F 




LDA A #3F 


A:=3F; 


A06A 


4C 




LOOP2 


INC A 


A:=A+1; 


A06B 


81 


60 




CMP A -60 


compare A to 60; 


A06D 


27 


E6 




BEQ FSTLIN 


if A=60goto FSTLIN; 


A06F 


8D 


A3 




BSR OUTCHR 


goto OUTCHR; 


A071 


20 


F7 




BRA LOOP2 


goto LOOP2; 



parallel interface port, then bringing the 
normally high data ready line low via 
interface output control line C2 for at 
least 1 ms, then returning the line high 
again. The data must be held stable on 
the interface output lines, however, until 
the printer acknowledges data receipt by 
bringing its normally high data accepted 
line momentarily low and then high 
again. This latter low to high transition 
signifies that the printer has accepted the 
character. The MP L control line C1 fed 
by this line has been programmed to see 
the low to high data accepted transition 
and responds by allowing the program 
to output the next sequential ASCII 
character. 

To set the printer's line width adjust- 
ment, you should use MIKBUG to 
change the data in hexadecimal memory 
locations A056 and A065 from 0D to 
00. This will eliminate the transmitted 
carriage returns and force the printer to 
print a full 40 column line. The line 
width control should then be adjusted 
for symmetrical margins. The characters 
will still be printed sequentially but will 
not be identical from line to line. 

Do not operate the printer more than 
a minute or so while running this diag- 
nostic. Continuous printing of full length 
lines with no spacing between characters 
overheats the solenoids on the print 
mechanism which may decrease its oper- 
ating life. 

If you are using the SWTPC PR-40 
printer with the SWTPC 6800 computer 
system, you may use the OUTCHR 
subroutine listed from address A014 
through A024 in the PRNTST diagnostic 
within your own program for outputting 
characters to the printer. The index 
register must be loaded with the starting 
address of the MP L parallel interface 
board feeding the printer. The character 
to be printed must be loaded into 
accumulator A and the contents of 
accumulator B are destroyed during the 
subroutine. 

Never install or remove the interface 
board when the system is powered up. 
Doing so is not only hazardous to the 
equipment, but bypasses the normal 
power up sequence required by the 
internal registers within the 6820 inte- 
grated circuit in order to guarantee 
proper operation." 



Note: MIKBUG 
Motorola Inc. 



is a trademark of 



Table J: Hexadecimal starting addresses of 
the parallel IO port interfaces used by 
MIKBUG. 

Port Address in Hexadecimal 



reserved for control interface) 



IO 


8000 


IO 1 


8004 


IO 2 


8008 


I03 


800C 


IO 4 


8010 


IO 5 


8014 


I06 


8018 


IO 7 


801 C 



20 




this type of print head, this printer rotates a 
long cylinder just beneath the print head. 
The length of the cylinder itself is a little 
longer than the head's printing width on the 
paper.' The cylinder has a uniform cyclic 
zigzag track formed on its outer circumfer- 
ence, running from the left side of the 
cylinder to the right side and then back to 
the left again. A small projection on the 
bottom of the print head rides in this track 
so that as the cylinder rotates, the print head 
moves back and forth from left to right. This 
technique moves the print head across the 
paper at a constant velocity except for the 
extreme ends, where nothing is being 
printed. This approach greatly simplifies the 
electronics needed to drive the printer since 
no head positioning circuitry is necessary. 
The cylinder itself is turned by an AC motor 



on the lower right hand side of the print 
mechanism. (See photo I.) A small ribbed 
nylon belt interconnecting the two rides on 
gear teeth of both the motor and cylinder. 
Also attached to the right side of the 
cylinder is a cam that actuates a roller arm 
microswitch riding on the cam. This is how 
the printer's electronic circuitry senses the 
start of line position of the print head. On 
the left side of the cylinder is an eccentric 
driven pawl arm that advances the paper one 
line for each revolution of the cylinder 
which is the same as one cycle of the print 
head. 

Let's go through a single cycle of opera- 
tion of a printed line where we will first 
assume the head is in rest position just left 
of center. When a line print command is 
initiated by the control circuitry, the motor 



Photo 2: This photograph 
displays the mechanical 
parts of the PR-40 printer. 
The seven solenoids can be 
seen to converge in a line 
at the print head. The po- 
sitioning mechanism for 
the printing head is seen as 
the spiral groove under the 
head mechanism. 



21 




ihmhmhmiQ 



Figure 3: Schematic diagram for the PR-40 impact printer. NAND gate 
IC14A converts the lower case ASCII characters to upper case ASCII 
characters. The printer outputs a line of data at a time. The data is output 
when a carriage return is received or 40 characters have been entered into the 
memory buffer. All ASCII control characters, except carriage return, are 
ignored since they are not printed anyway. All resistors in this circuit are 
measured in ohms and are 0.25 W. 



1- 

Q. 


5 £ 


< UJ 


zh 


1- u 


£ ^ 


< u 




Q< 





22 



starts and the head begins to move from the 
center position toward the far left side of 
the printer where the head reverses direc- 
tion. This nonprint dead zone gives the 
motor, cylinder and print head time to 
attain full speed. As the head begins its 
movement from left to right, the cam 
actuated microswitch opens telling the elec- 
tronic circuitry to start sending solenoid 
driving pulses for the character. Somewhere 
before the print head reaches the far right 
hand edge of the paper, the solenoid pulses 
will cease while the head continues to move. 
When the head reaches the right end of its 
travel, it will mechanically reverse direction 
and begin to move back toward the center of 
the printer. During this return movement, 
the pawl arm will rotate the platen one line 
for the line feed. The motor is then turned 
off just to the left of center where it started 
originally. With our controller for this mech- 
anism, character data is not accepted by 
the printer's circuitry during an actual print 
cycle; however, feeding continual print data 
from a computer to the printer may take 
place so fast that the print motor may never 
appear to stop between repeatedly printed 
lines although it actually does. 

The operation of the printing ribbon used 
on the unit is also amazingly simple. A 
ratchet technique not only advances the 
ribbon incrementally for each cycle of the 
print head but automatically reverses it 
when it reaches the end of one of the two 
spools. 

The Electronics 

The electronic circuitry designed to drive 
the print mechanism can vary from nothing 
but motor and solenoid drivers constantly 
serviced by the microprocessor to a fully 
self-contained hardware control unit with 



Table 2: Power pins for the circuit of figure 
3. 

Number Device +5 V GND -5 V -12 V 



IC1 


3351 


26 




IC2 


5241 


12 




IC3 


7407 


14 


7 


1C4 


7490 


5 


10 


IC5 


555 


8 


1 


IC6 


74121 


14 


7 


IC7 


7407 


14 


7 


IC8 


7474 


14 


7 


IC9 


7420 


14 


7 


IC10 


555 


14 


8 


IC11 


7400 


14 


7 


IC12 


7404 


14 


7 


IC13 


7430 


14 


7 


IC14 


7400 


14 


7 


IC15 


7402 


14 


7 


IC16 


7400 


14 


7 


IC17 


7805 




3 


IC18 


7474 


14 


7 



28 



27 
23,23 



memory needing only 7 bit parallel ASCII 
data and a data ready strobe control line 
from the computer. The printer electronics 
of the PR-40 fits into the latter category. 
The PR-40's controller has its own 40 
character first in first out memory allowing 
the computer to send character data at 
whatever speed it wishes. The entire line is 
printed upon receipt of a carriage return, 
hexadecimal OD, or automatically whenever 
the 40 character line buffer has been filled. 
All control characters with the exception of 
a carriage return are ignored by the printer. 
They are not stored in the buffer line 
memory since they cannot be printed any- 
way. Repeated line feeds are initiated by 
sending repeated carriage return control 
commands. Since the controller generates 
upper case ASCII characters only, all lower 




Photo 3: A view from the bottom of the PR-40 impact printer displaying the 
electronic circuitry of the system. The circuit board at the top left of the 
picture is the circuit for the power supply as described in figure 2. The circuit 
at the bottom of the picture is the electronic assembly for the print head 
driver. The large chip at the bottom left of the picture is the first in first out 
memory chip. The IC chip directly above it is the read only memory 
character generator. 



23 



The PR-40 alphanu- 
meric printer is manu- 
factured by Southwest 
Technical Products Corp, 
219 W Rhapsody, San 
Antonio TX 78216. It is 
sold in kit form only. The 
kit number is #PR-40 for 
$250 post paid in the 
United States. The kit 
includes the print mech- 
anism, chassis, circuit 
boards, components, 

power supply, assembly 
instructions, one ribbon 
and one roll of paper. 



case characters sent to the controller are 
transposed to their upper case equivalent 
before printing. The printer's line buffer 
memory is automatically cleared by a hard- 
ware power up reset circuit when printer 
power is first applied. The printer's triac 
controlled motor is powered by a 1 20 VAC 
secondary on the power supply's power 
transformer, as shown in figure 2. This not 
only provides power line isolation but allows 
the entire unit to be run on either 120 VAC 
or European 240 VAC power systems since 
the power transformer has two primary 
windings which may be either parallel or 
series connected. 

The seven ASCII parallel data input lines, 
data ready, and data accepted control lines 
are all TTL compatible. The inputs represent 
a maximum of two standard TTL loads 
while the data accepted output will drive ten 
standard TTL loads. Data is presented to the 
printer by storing the selected ASCII data on 
the seven data input lines and strobing the 
normally high, logic 1, data ready input line 
low. This line should go low, logic 0, for at 
least 1 [is and when it does the normally 
high data accepted will also go low. The 
character is not actually loaded until the 
data ready input is returned to its normally 
high state. The data accepted line will then 
normally return high as well, indicating that 
the character has been loaded. However, 
when loading the 40th character on a print 
line or a carriage return command, this data 
accepted line will not return high until all 
the previously stored data has been printed 
and the printer memory is ready for more 
data. The PR-40's printer controller will 
ignore all data sent to it while the data 
accepted line is low. So you will usually 
want to make sure the data accepted output 
line is high before sending the controller 
more data to be printed. 

If you are careful not to output data 
faster than one character per jks and allow a 
minimum one second delay before sending 
data after sending a carriage return or the 
40th character of each line then you may 
avoid using the data accepted line altogether. 
However, using the data accepted line will 
give your system the fastest possible print 
speed. 

How It Works 

All ASCII character data is presented to 
the first in first out memory, IC1, through 
hex inverter and buffer, IC12. NAND gate 
IC14A makes any necessary conversions 
from lower to upper case characters. 8 input 
NAND gate IC13 monitors the incoming 
ASCII data in search of a carriage return, 
hexadecimal 0D, control command. If it 



decodes a carriage return it will prepare 
normally high control flip flop IC8A to go 
low on the falling edge of the data ready 
control signal. NOR gate IC15A decodes all 
control characters and along with IC15B 
inhibits any control characters from being 
loaded into the buffer memory. NAND gate 
IC9A is responsible for generating the data 
accepted control output whenever data has 
been accepted by the buffer memory or 
acknowledged by the control character de- 
code logic. It also inhibits the data accepted 
output while the printer is in the process of 
printing a line. 

Control flip flop IC8A's Q output is high 
when the printer is in the idle state. A buffer 
memory full signal decoded by NOR gate 
IC15D or a decoded carriage return com- 
mand by I CI 3 resets this flip flop low which 
turns the printer's motor on through transis- 
tors Q1 and Q2 located on the power supply 
board which starts a line print sequence. 

When the print head advances to the start 
of line position, the roller arm microswitch 
changes states which flips RS latch NAND 
gate IC11D low which allows free running 
oscillator, IC1 0, to feed divide by 2 flip flop, 
IC8B. This divide by 2 feeds both the dot 
counter, IC4, and solenoid timer, IC6. This 
solenoid timer is used to set the on time of 
the printer's solenoids. If set too long, the 
solenoids will overheat; if set too short, the 
printed lines will be too light. An on time 
duration of 400 jus is the best compromise 
setting. Decode counter IC4 has its B and C 
outputs tied back to its zero reset inputs 
forcing it to become a modulo 6 counter. As 
the counter progresses from to 4 inclusive, 
the selected character lines are decoded by 
the read only memory, IC2, using the ASCII 
data fed to it by the buffer memory, IC1, 
and fed onto the solenoids through buffers 
IC3 and IC7 and Darlington drivers Q1 and 
Q7. Counter state 5 is decoded by the read 
only memory as a blank for the one dot 
space necessary to separate the printed 
characters. In the latter phase of the five 
count the memory buffer is shifted, the 
counter resets, and the sequence repeats. 
When the memory buffer finally empties, 
the read only memory is disabled and blanks 
the output for the rest of the print cycle. 
When the still moving print head reaches its 
normal rest position, the roller arm micro- 
switch again changes states. This time RS 
latch NAND gate I Cl 1 C flips low, setting 
control flip flop, IC8A, back to normally 
high state. Timer IC5 is a power up clear 
circuit which empties the first in first out 
buffer memory and helps prevent random 
firing of the print solenoids during power 
up." 



24 



The 

POLY 88 
Microcomputer 

System 

If you are into computers or considering a system, the 
POLY 88 is the machine to contemplate. 

HARDWARE 

• Popular 8080 central processor • Single-board CPU 

with ROM, RAM, vectored interrupt, real time clock, 

single-step logic and serial I/O • Video interface card - 

generates video to TV monitor and provides parallel 

keyboard input port • Serial and cassette mini-cards plug 

directly into CPU with ribbon cables • Cassette 

• ROM monitor with powerful debugger, video software, 

bootstrap loader • Backplane and power supply on one 

board simplifies construction • Rugged 6 amp power 

supply • All circuit boards are high quality, double-sided 

with plated-through holes • System is compatible with 

a wide range of Altair peripherals • Minimum point to 

point wiring means that the POLY 88 kit can go 

together in three evenings! 

ABOUT SOFTWARE 

Software is the reason the POLY 88 was designed. The 

operator can proceed from higher level languages like 

BASIC to developing machine code with the aid of our 

assembler. Our BASIC is a full 8K BASIC with character 

and byte manipulation. Best of all, the programmer is 

finally free of the teletype emulation mode so the video 

display can be used to full advantage. 

The video display provides a unique opportunity to write 

new types of programs and games. Characters (16 lines 

of 64) and graphics (48 by 128 grid) are part of the 

processor's memory, so the display may be altered 

rapidly — the entire screen written in less than 20 

milliseconds. 
POLY 88 hardware provides many 
additional features that 
programmers have come to expect, 
such as vectored interrupt and real 

time clock. 




POLY- 83 



Dc: 



See it at your local computer store. 



ARE YOU NEW TO COMPUTERS? 
The POLY 88 was designed for ease of use. No one 
should have to learn all the inner workings of computers 
just to enjoy one at a reasonable price. With the POLY 
88, you can "play"pre-developed programs or explore 
the world of computer languages as your interests expand. 

THE POLY 88 IS FOR EVERYONE 
Want to develop a new computer language? Want to 
fight Klingons? The POLY 88 provides a firm foundation 
upon which to build your interests and develop your skills. 

POLY 88 SYSTEM PRICES: 

SYSTEM 1 — Kit includes 8080 vectored interrupt 

processor with real time clock, Vi K of RAM and IK 

monitor on ROM: Video Terminal Interface displays 16 

lines of 32 characters on a video screen and has a 

keyboard input port; cabinet, backplane, and power 

supply; complete assembly, operation and theory 

manual. $595. 

SYSTEM 2 — System 1 plus 64 character line option and 

Byte/biphase cassette interface kit. $690. 

SYSTEM 3 — System 2 plus 8K of RAM with BASIC 

and assembler programs on cassette tape. $990. 

SYSTEM 4 — The complete kit. It includes system 3 and 

TV monitor, keyboard and cassette recorder with all 

necessary cables and connectors. $1350. 

SYSTEM 7 — System 4 assembled, tested and ready to 

run. $1750. 

ACCESSORIES — 8K RAM kit, $300. Assembled $385 

POLY I/O Ideaboard, hardware prototyping kit board. $55. 

Analog Interface (1 channel) kit. $145. 

Prices effective until January 15, 1976. Prepaid orders shipped postpaid. 



PolyMorphic 
Systems 



737 S. Kellogg, Goleta, CA 93017 
(805) 967-2351 







. 






Cassette Transports for the 

"Roll Your Own" Hobbyist 



William H Freeman 
816 Meadowlark Ln 
Glenview IL 60025 



Use of the Phillips Compact Cassette as a 
storage medium has been well established. 
Articles in BYTE and other publications 
have made the audio cassette just about the 
only storage device for the computer hobby- 
ist. However, not enough attention has been 
given to the machine in which the cassette is 
operated. From various articles the usual 
transport mechanism is usually referred to as 
a cheapie or $30 cassette recorder. The usual 
control is a relay used to turn on the entire 
device. I regard this method as less than 
satisfactory and suggest that there are better 
ways. 

When the low cost cassette machine is 




Photo 1: The Ami I on A9 cassette transport. It is similar to the A 7 transport 
varying only in a different head mount and the lack of an index counter on 
the A 7 model. 



turned on or off with a relay, two dif- 
ficulties are immediately apparent. First the 
pinch roller is always engaged, which can 
cause a dent in the roller if left too long in 
this position. The dent will cause serious 
wows in the tape speed. Second, the startup 
time will be excessively long. This leads to 
the conclusion that the entire tape transport 
mechanism should be controlled by the 
computer. All of the transport functions, 
play, stop, rewind and fast forward, should 
be available on command by the computer. 

Audio cassette transports which will meet 
the requirement of being controlled by logic 
signals are available and can be purchased by 
the computer hobbyist. These transports 
have usually been available to the original 
equipment manufacturer (OEM), but the 
various manufacturers have indicated that 
they will sell to individuals or groups. One of 
the manufacturers of cassette transports, the 
Economy Company, has been actively pro- 
moting use of their deck for data storage, 
but more about it later. 

To the best of my knowledge, there are 
only four companies in the US making and 
selling "bare bones" cassette transports. One 
of these companies, TELEX Communica- 
tions, only has a manually operated trans- 
port, which cannot be controlled by a 
computer and is of no real interest to the 
computer hobbyist, even though it is a well 
constructed, rugged unit. The three re- 
maining companies, Amilon Corporation, 
the Economy Company and the Mincom 
Division (Wollensak) of 3M, all have trans- 
ports which are amenable to logic control 
since they have solenoids doing the work. 

The Amilon Corp has two cassette trans- 
port models which might be used by the 
computer hobbyist. One model, the A9, is 
primarily an audio unit with mono or stereo 
heads for playing or recording usual audio 
type information. The other model, the A7, 
has characteristics slanted to the data storage 
business. The two machines are very much 
alike structurally, being built on the same 
basic frame. They are the same in size and 
weight, and require the same electrical in- 
puts. Table 1 lists the performance de- 
tails and shows the similarity of the two 
transports. 

Optical end of tape sensing is available as 



26 





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an option. The lamp used is a 5 V, 100,000 
hour rated lamp. Four kinds of cassette 
sensing options are available using up to four 
micro switches to sense the cassette in place, 
record tab A and tab B and side A. Side A 
sensing is detecting the off center slot on the 
back edge of the cassette which is present in 
a computer cassette. 

Both the capstan and reel motors are AC 
induction motors which means long, reliable 
operation with no brush noise problems. The 
capstan motor is a synchronous one and is 
used to drive only the capstan, insuring 
accurate speed. The other motor is used to 
drive either the takeup spindle in the play, 
record, and fast forward modes or to drive 
the supply spindle in the rewind mode. 
Amilon claims this is the reason for the 
excellent wow and flutter performance as 
there is no motor acting as a drag when in 
the play or record mode. The mechanical 
structure is solid and stiff, assuring con- 
tinued alignment of all parts. In particular, 
the pinch roller is mechanically isolated 
from the heads and is mounted on self- 
aligning instrument ball bearings to give even 
pressure on the capstan and minimizing any 
skew of the roller. 



I was greatly impressed with the quality 
and attention to detail in this machine when 
the A9 model was demonstrated. Amilon 
Corp is also involved with digital cassette 
transports and some of their thinking has 
rubbed off on the audio cassette transport's 
design, to the audio transport's advantage. 
Photo 1 shows the Model A9 transport. The 
A7 model is almost identical, differing only 
in the head mount and its lack of an index 
counter. 

You want to know what it costs? OK! 
Prices for the A7 transport, the data unit, 
start at $210 for one ($113.51 each in 
quantities of 100) which includes a precision 
head mount and a two track read and write 
head. End of tape sensing and cassette 
sensing switches are extra. Prices for the A9 
transport start at $164.75 for one ($87.79 
each in quantities of 100) which includes 
standard head mounts, stereo erase, and 
record and play heads. End of tape and 
cassette sensing switches are extra. 

Next on the list of transports, alpha- 
betically, is the Economy Company with its 
Phi-Deck. The Economy Co is a school book 
publisher for elementary education. Some 
years ago they added educational cassette 



Table 1: Comparison of 
the A 7 and A9 cassette 
transports manufactured 
by A mi I on comparing 
speed, accuracy, and 
power requirements of the 
two units. 



Play or Record Speed 

Speed Accuracy 

Wow and Flutter 

Reel Controlled Search Speed 



A7 

1.875 to 10.0 in per sec t 
4.763 to 25.4 cm per sec 

±2% at any speed 

not stated 

50 in per sec average 
127 cm per sec average 



A9 

1 .875 or 3.75 in per sec* 
4.763 or 9.53 cm per sec 

±1% (±0.3% available) at any speed 

<0.1% NAB weighted 

not available 



Fast Wind or Rewind 


not available 


70 sec for C60 cassette 


Start Time 


<40 ms 


<300 ms 


with speedup circuit 


<25 ms 




Stop Time 


<60ms 


<50 ms 


Sensor Switches 


SPDT 


SPDT 


Operating Humidity 




to 95% noncondensing 


Operating Temperature 




+5° to+50°C 


Storage Temperature 




-20° to+70°C 


Size 




5.16 by 7.00 by 4.61 in 



Weight 

Capstan motor (synchronous) 

Reel motor (fast mode) 

(play mode) 

Solenoids 

"fTen different speeds available: 

*Dual speed pulley available. 



13.10by 17.78by 11.71 cm 

5.00 pounds 
2.27 kilograms 

1 1 7 V ± 1 0%, 50 or 60 Hz, 1 1 W 

24 V ± 10%, 50 or 60 Hz, 13 W 
18 V ± 10%, 50 or 60 Hz, 8W 

24 VDC, ±5%, 600 mA 

1.875,2.0,3.0,4.0,5.0,6.0, 7.0,8.0,9.0, 10.0 in per sec 

4.763, 5.1,7.6, 10.2, 12.7, 15.2, 1 7.8, 20.3, 22.86, 25.4 cm per sec 



28 



scam 

fOFTUfl 





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Introducing SCELBAL, 
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Describes "Monitor Control" 
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lAPniBUI.1 imU inid Telephone: 203/874-1573 







Photo 2: The Phi -Deck Super Deck model manufactured by the Economy 
Company. This model allows varying tape speeds by varying the voltage to 
the capstan motor. The frame of the cassette transport is die cast } reducing 
alignment problems and making it quite rigid. 



publishing to their product line. This pro- 
duced demand for an audio unit to play the 
cassettes, with Phi-Deck the result. Over a 
year ago I saw the Phi-Deck demonstrated. 
Since that time the number of Phi-Deck 
models has increased to three; the advanced 
model is shown in photo 2. In addition to 
the transports themselves, the Economy Co 
is offering control boards to do all the tricky 
functions on command. The three models 
are referred to as fixed speed, variable speed, 
and Super Deck; their performance is tabu- 
lated in table 2. At least one personal 
computing manufacturer (Digital Group) is 
now offering Phi-Deck as part of a system 
product at quite reasonable prices. 

As is usually the case, the performance 
figures in table 2 do not tell the whole story. 
All three transports have four DC motors. 
One motor drives just the capstan, the speed 
being maintained by a voltage regulator 
supplying current to the capstan drive 
motor. Another motor is used to drive the 
supply spindle. Still another is used to drive 
the takeup spindle. And the fourth motor 
actuates the yoke on which are mounted the 
heads and the pinch roller by means of a 
Geneva movement. (A Geneva movement 
translates rotary motion into linear motion. 
One revolution of the motor pulls the heads 
and pinch roller into position and another 
revolution moves them out of position. The 
motor always turns in the same direction!) 

These DC motors are ideal for direct 
control with transistors since they run off 



Table 2: Comparison of the three cassette transports manufactured by the Economy Company giving electrical comparisons and 
the physical dimensions and weight of the transports. 



Speeds 



Wow and Flutter 

Bit to Bit Jitter 

Speed Accuracy 

Start Time 

Stop Time 

Forward and Rewind Time 

Power Required 

Size 

Weight 



Fixed 

1 .88 in per sec standard 
2.00,3.75,4.00, 5.00,6.00 
in per sec optional 

4.77 cm per sec standard 
5.08,9.53, 10.16, 12.70, 
1 5.24 cm per sec optional 

<0.25% at 1.88 in per sec 
4.77 cm per sec 

not stated 

not stated 
<100 ms 
<100 ms 

<30 sec for C60 cassette 
+ 12 VDCat900 mA 



2.60 by 5.40 by 6.30 in 
6.60 by 13.72 by 16.00 cm 

2.20 pounds 
1.00 kilograms 



Variable 

0.40 to 20.00 in per sec 
1 .02 to 50.80 cm per sec 



<0.25% at 1 .88 in per sec 
4.77 cm per sec 

±2% 

±3% 
<100 ms 
<100 ms 

<30 sec for C60 cassette 
+ 12 VDCat900 mA 



2.60 by 5.40 by 6.30 in 
6.60 by 13.72 by 16.00 cm 



Super 

1 .00 to 1 0.00 in per sec standard 

0.40 to 3.00, 0.60 to 5.50, 0.85 to 8.50 

in per sec optional 

2.54 to 25.40 cm per sec standard 
1.02 to 7.62, 1.52 to 13.97, 2.16 to 
21 .59 cm per sec optional 

not stated 



±2% 

±3% 

<100 ms 

<100 ms 

<30 sec for C60 cassette 

+18VDC, -18VDC, +11 VDC, +7 VDC, 
+5 VDC 

3.00 by 5.50 by 6.20 in 
7.62 by 13.97 by 15.75 cm 



2.20 pounds 
1 .00 kilograms 



2.80 pounds 
1 .27 kilograms 



30 






12 V. A transistor in series with the motor 
acts as a switch controlled directly from the 
* logic circuits. Very straightforward and sim- 
ple. The logic and control circuits, which can 
be purchased or built, can do a lot of elegant 
performing on the part of the transport. In 
connection with end of tape and beginning 
of tape sensing options, one can cause the 
cassette to play to the end, then rewind to 
the beginning, stop or start playing all over 
again. By controlling the regulator supplying 
the capstan motor, different speeds of play- 
ing can be obtained. Cassette in place and 
record tab sensing are also options that are 
available. With the variable speed model, a 
different pulley is used for each speed range. 
The Super Deck model covers its entire 
speed range with only one pulley. 

Of the three models, the one I rec- 
ommend is the Super Deck as shown 
in photo 2. It has a diecast frame, 
making it quite rigid, reducing alignment 
maintenance problems. The other two 
models, the fixed speed and the variable 
speed, have a sheet metal frame that is 
somewhat flimsy and leaves something to be 
desired in ruggedness. Literature supplied by 
the Economy Co suggests that the Super 
Deck model was designed with data applica- 
tions in mind, and as such, would be more 
attractive to the computer hobbyist. 

The price of the fixed speed Phi-Deck, 
including a stereo head, is listed at $94.50 
for one. The variable speed model, with all 
options, lists for $99.50, with either a two 
halftrack digital head or a regular audio 
stereo head. The Super Deck, with all 
control and sensing options, lists for $169 
for just one at the time this was written. 
Electronic control board, remote control 
boxes and power supplies are also available. 

Because of my past experience with 
maintenance problems, I have a prejudice 
against the use of DC motors. However, 
from data supplied by the Economy Co, it 
appears that they have made a very strong 
effort to improve the performance of their 
DC motors. Their data indicates that a mean 
time before failure of 5000 hours is a 
reasonable value. This would mean 2.5 years 
of operating time, assuming 40 hours a week 
for 50 weeks a year. 

I have two objections to DC motors. First 
is the fact that the motors have brushes and 
commutators which wear, the brushes prin- 
cipally, and need to be replaced at intervals. 
In the case of the small motors being 
>^onsidered, many have no provision for 
.eplacing the brushes, so one must replace 
the whole motor. The second objection is 
that the brushes can cause noise in the 
associated circuitry, requiring additional 




Photo 3: Wo/lensak Model 9576 and 9577 cassette transports. The two 
transports are identical, except the 95 77 has an optical end of tape sensing 
unit. The basic construction consists of two heavy metal plates separated by 
standoffs to form the frame. A flat panel supplied by the user is put on the 
top of the transport to protect the inner mechanisms. 



Play and Record Speed 

Speed Accuracy 

Wow and Flutter 

Rewind and Fast Forward Times 

Solenoids 

Light Source (Model 9577) 

Sensor (Model 9577) 

Size 

Motor Power 



Model 9576 and 9577 

1.875 in per sec 
4.763 cm per sec 

±2% 

<0.25% 

45 sec for C60 cassette 

24 VDC 72 ohms 

subminiature lamp 5.0 VDC @ 0.075 A 

2N5778 Photodarlington 

5.63 by 6.75 by 4.78 in 
14.29 by 17.1 5 by 12.14cm 

117 V, 50 or 60 Hz, 10 W 



parts to suppress it. AC induction motors 
have no brushes, hence no noise or wear 
problems. With oilite sleeve bearings they 
run quietly for a long, long time. 

The last transport models to be described 
are made by the Mincom Division of the 3M 
Company. There are three versions, very 
much alike: Model 9575, Model 9576 and 
Model 9577. Model 9575 is a manually 
controlled mechanism and is of no interest 
to us. Models 9576 and 9577 are solenoid 
controlled mechanisms which are what wc 
want. All models have the same basic drive 



Table 3: Performance 
characteristics of the cas- 
sette transports manu- 
factured by Wollensak. 
The two models are the 
same except that the 9577 
has an optical end of tape 
sensing unit that the 9576 
does not have. 






31 


















Mean Time 




Price 


Performance 


Before Failure 


AMILON 


high 


excellent 


very good 


PHI-DECK 


medium 


very good 


very good 


WOLLENSAK 


medium 


very good 


excellent 



Table 4: The author's 
comparison of the best 
tape transports manufac- 
tured by Am Hon, Econo- 
my Company, and Wollen- 
sak. The ratings are in rela- 
tion to how well the objec- 
tives of low price, high 
performance, and a long 
mean time before failure, 
are achieved. 



arrangement. An AC induction motor, 
shaded pole, drives a large flywheel through 
a rubber tired idler. The flywheel is on the 
capstan shaft. The supply and takeup 
spindles are driven from the flywheel with 
rubber tired idlers. No belts are used in the 
drive mechanism. There is one belt but it is 
used to run the index counter. In the two 
models of interest, three solenoids control 
the operating functions. One solenoid is 
pulled up for play or record; another is 
pulled up for fast forward; and a third for 
rewind. 

The Model 9576 and Model 9577 are 
identical in all respects except that the 
Model 9577 has an optical sensing circuit 
included. This optical sensing consists of a 
small 5 V lamp and a phototransistor. This 
will provide end of tape and beginning of 
tape sensing. Table 3 lists the performance 
of both models. 

Photo 3 shows the basic construction of 
the Wollensak transport, consisting of two 
heavy plates separated by standoffs forming 
the frame. The user must supply some kind 
of flat panel with cutouts for the cassette 
tray, the eject lever and the index counter. 
Four screws will attach the unit to this 
panel. This transport, like its big brother 
units made by Wollensak, is well built and 
should have a long service life with a 
minimum of maintenance. My experience 
with the full size Wollensak cassette units is 
that they run, and run, and run. 

The latest prices available to me are 
$79.50 for Model 9576 and $85.75 for 
Model 9577 in quantities of 1-9. In 100 lot 
quantities prices are $65 and $71.25, re- 
spectively. Heads for the transport are extra. 

How should these three cassette trans- 
ports be evaluated? We can use three cri- 
teria: price, performance and reliability. 
Price is easy, just look at the figures. 
Performance and reliability are not so easy 
to establish because each potential user will 
assign different values to the various details 
of performance depending on the end objec- 
tive and his or her bias. My bias has already 
been stated. My evaluations are given in 
table 4. 

Some explanation may be necessary. 
Amilon is rated excellent in performance 
because of its very low wow and flutter 



figure and its tight speed control with a 
synchronous motor. Wollensak is rated ex- 
cellent in the mean time before failure 
column because of my past experience with 
Wollensak cassette units covering more than 
six years of usage in the school environment. 

If I had an overflowing purse, I would 
buy the Amilon unit because of its excellent 
performance. Price is, however, a very de- 
manding factor, so the Wollensak is my 
choice as the best buy. The Phi-Deck comes 
in very close in this decision. It is a certainty 
that not all readers will agree with this 
evaluation, which is certainly your privilege. 
The individual who is putting out the green 
stuff is entitled to make his or her own 
choice based on what is felt to be important. 
As they say, 'That's what makes a horse 
race." 

Where can you get one of these cassette 
transports? In alphabetical order: for an 
Amilon deck write to Leonard Rosenblatt, 
Amilon Corp, 49-12 30th Av, Woodside NY 
11377; for a Phi-Deck you can find the 
address in ads in BYTE, but here it is 
anyway — The Economy Co, Triple I Divi- 
sion, 1901 N Walnut, Oklahoma City OK 
73105; and for the Wollensak deck, write to 
Scott Goff, Sales Manager, Wollensak OEM 
Products, Mincom Division, 3M Co, 3M 
Center, St Paul MN 55101. 

As a kind of post script to this article, I 
have included a few words of wisdom about 
using cassette transports, or any tape 
machine. Preventive maintenance will keep 
your cassette transport running without 
problems. Regularly do the following: 

1. Clean the capstan, pinch roller, heads 
and guides after every 10 hours of 
operation. Use a good fluorocarbon, 
low toxicity head cleaner; one that 
will not attack rubber or plastic parts. 

2. Keep all parts as dust free as possible. 
Use a dust cover over the transport 
when not in use. 

3. Lubricate as often as the manufacturer 
specifies. Do not overlubricate; be 
sparing with the oil. 

4. Demagnetize the heads, capstan and 
guides with a good head demagnetizer 
after every 10 hours of operation. 

Overall performance will be considerably 
affected by the quality of the cassette used. 
Use a good to high quality cassette. Cheap 
cassettes will have poor tape quality and, 
even worse, poor mechanical performance 
which will adversely affect the tape speeds 
You will find that with the better to best 
tapes, you get better recordings with better 
frequency response and all around better 
performance." 



32 



Meet the Challenger." 




The Challenger 
Self Portrait 



The new price and performance champ from OSI. 



He's got his act together! 

Even our lowest-cost Challenger 
comes fully assembled, complete 
with a 500 ns 6502A, serial interface, 
1 ,024 words of memory and a 
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for easy expansion with an 8-slot 
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capability, and a power supply 
heavy enough to handle a full 
complement of system boards. Our 
4K Challenger comes ready to run 
BASIC minutes after you unpack it. 
And there's more. 

He packs some heavy hardware. 

You've never seen memory and 
interface options like these — not at 
our prices, fully assembled! 4K 
RAM memory boards $139! (see 
below). Single drive OSI Challenger 
Floppy Disk $990! Dual drive 
Floppy $1490! Plus 8K PROM 
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OSI has full software support for our 
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You can order The Challenger with 
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cycle time, or with a 6800 for 1 
microsecond cycle time. And with 



our CPU Expander Board, you 

can always update to any new CPU 

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memory. Will run Tiny BASIC with- 
out expansion. $529. 
The OSI Challenger 65V-4K. NO 
NEED for an expensive terminal. 
Connects to your ASCII keyboard 
and video monitor through included 
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software utility that simulates a 
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The OSI Challenger 68-1 K. Based 
on 6800 CPU. For the casual 
hobbyist, smaller systems. The 
Challenger 68 series comes only in 
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utilities package. $459. 
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Buy 12K or larger Challenger 65 
system and we include Extended 
BASIC FREE! 




i 



OSI Challenger Floppy Disk System. 
Fully assembled, for use with OSI 
Computers only. $990 Single drive 
$1490 Dual drive. 
OSI Audio Cassette Interface. 
Comes assembled, but with room 
for you to populate with A/D and 
D/A chips later. (OSI 430 based) $89 
And all the baseboards and kits of 
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OK, OSI, I'm ready to buy! 

To order your Challenger System, 
send the total amount of your 
purchase plus $4.00 for shipping and 
insurance (plus sales tax for Ohio 
orders) by personal money order or 
check. Or indicate all numbers 
on your BankAmericard or Master 
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Or send a 20% (non-refundable) 
deposit to receive your order C.O.D. 
Delivery is typically 60 days (except 
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must clear before shipment can be 
made). Deliveries are scheduled on 
a first ordered, first shipped basis. 

Name 



Address. 
City 



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-Zip_ 



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Bank card info Inter Bank#. 

Expiration Date 

Account # 



Check □ M. O. □ BAC D MCQ 
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□ $1.00 enclosed 
for complete 
OSI Catalog. 



OHIO SCIENTIFIC INSTRUMENTS 

Dept. B 11679 HAYDEN STREET, HIRAM, OH 44234 




(216) 569-7945 



Continued from page 10 

at the servo and in the displays used to 
monitor the position count. 

The program is quite simple: It generates 
a positive going pulse on the bit line of the 
PI A output port, a pulse which lasts from 
1 ms in length to 1 + 0.012 n ms where n is 



an 8 bit number which is incremented once 
each time around the outer loop of the 
program. The 0.012 ms factor is based on 
the processor's clock at the time of the test, ' 
500 kHz, and the 6 state loop at addresses 
20 IF and 2020 which times the width of the 
variable portion of the pulse. With the servo 
illustrated in photo 1, the wiring used was as 



PEN AT LOCATION 




COLOR KEY- 

MOVABLE SERVO ARM AND 
ITS ARC RANGE WITH FIXED 
SERVO POSITION SHOWN. 

FIXED SERVO ARM AND ITS 

ARC RANGE. 

ENVELOPE OF TYPICAL 

MOVABLE SERVO POSITIONS. 



Figure 2: This diagram shows the concept of 
how to build a plotting bed based upon two 
model aircraft servomechanisms. The 
method of building consists of fixing one 
servo to the plotting bed, with a lever arm of 
length R. At the end of that lever arm, fix 
the second servo with a second lever arm of 
length R also. The end of the second arm 
should have a pen affixed to a solenoid 
mechanism or other actuator, allowing the 
pen to be raised or lowered. Due to weight 
considerations, the second servo should be 



mounted so that it slides on a teflon skid or 
rolls on some form of loose ball roller. The 
mathematics of calculating X and Y given 
angles and 6 is shown in the drawing. To 
invert the calculation requires use of a 
reiterating calculation to a set of and 6 
values which solves the desired X and Y 
position. To use this plotter requires a 
system which has sufficient memory to run r^ 
fixed point trigonometric package with ax. 
least 16 bits of precision, assuming a 13 bit 
precision for the angular parameters of the 
servos. 



34 






follows: +5 V was the red wire, ground was 
the black wire, and the TTL output of PI A 
bit zero was used to drive the blue wire. 

The results of the test are somewhat 
interesting. When this program was run, the 
servo was observed to have a total travel of 
180° rotational! y. A unique relationship 
between the integer pulse width parameter 
stored in DA TA in this program and the 
shaft position was observed, but the mini- 
mum acceptable pulse width for the device 
we purchased was probably 1.3 ms. The 
reason for this conclusion is that the servo 
illustrated two regimes of settings: For 
counts of 00 to J 9 hexadecimal (0 to 25 
decimal) it swept out clockwise motion from 
180° to 0° (relative angles). The motion was 
partitioned into very noticeable and large 
steps over this range. Then, from counts 19 
to D6 the servo swept counterclockwise 
from 180° to 0° with what looked like 
roughly linear steps. This range of 189 steps 
is about 0.95° per step. At the high end of 
the count range, D9, the servo hit its limit 
stop. Thus, based on this experiment, the 
actual numbers work out as follows: 



Minimum pulse width: 
1 +0.012X25= 1.3ms 



Maximum pulse width: 
1 +0.01 2 X 21 4 = 3.6 ms 

In using this servo, or any similar mechanism 
for an experimental project, readers would 
want to investigate the linearity of the 
position output with respect to the control 
parameter, and use a higher resolution 
timing method. For example, to make the 
world's least expensive plotter, using a 13 bit 
counter with a 2 MHz crystal clock, decimal 
counts of from 2600 to 7200 would cover 
the range of timing values found above, 
giving a control parameter range of to 
4600, approximately 0.04° per step as- 
suming linear characteristics. Using trigonom- 
etry, this corresponds to an arc motion of 
0.00683 inches per step at the end of a 
10 inch lever arm (0. 1 7 mm per step at the 
end of a 25 cm lever arm). Using two such 
servos, and working out the trigonometry of 
two connected lever arms, one on a servo 
fixed to the plane and one on a servo at the 
end of the fixed servo's lever arm, it should 
be possible to homebrew an XY plotter for 
less than $100 by just buying two such 
model aircraft servos. Since I have no en- 
gineering specs yet on these devices, I can 't 
say how accurate the plotter would be, but 
it would certainly draw! See figure 2. ■ 




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35 












A 6502 Op Code Table 



Lemuel A Fugitt 
11316 Linares St 
San Diego CA 92129 



Table 1: An explanation 
of the abbreviations used 
in the 6502 reference 
chart. 



LEAST 

SIGNIFICANT 
4 BITS 



abs: absolute. 

abx: indexed absolute using x register. 

ace: accumulator. 

aby: indexed absolute using y register. 

i,x: indexed indirect using x register. 

i,y: indexed indirect using y register. 

imm: immediate. 

imp: implied. 

ind: absolute indirect. 

rel: relative. 

zer: zero page. 

zpx: indexed zero page using x register. 

zpy: indexed zero page using y register. 

*: not implemented. 



MOST SIGNIFICANT 4 BITS 



Here's a nice compact reference chart to 
help you debug those hexadecimal dumps 
from your 6502 microprocessor. To use the 
table, find the most significant digit along 
the top of the chart and follow the column 
down until you reach the value of the least 
significant bit of the hexadecimal code on 
the horizontal row. You now have not only 
the mnemonic but also the addressing mode 
being used. Table 1 is an explanation of the 
abbreviations used in the chart. ■ 



1 








1 


2 


3 


4 


5 


6 


7 


8 


9 


A 


B 


C 


D 


E 


F 




BRK 
imp 


BPL 
rel 


JSR 
abs 


BMI 
rel 


RTI 
imp 


BVC 
rel 


RTS 

imp 


BVS 
rel 


* 


BCC 
rel 


LDY 
imm 


BCS 
rel 


CPY 
imm 


BNE 
rel 


CPX 

imm 


BEQ 
rel 




1 


ORA 

i,x 


ORA 

i,y 


AND 
i,x 


AND 
i.V 


EOR 

i,x 


EOR 
i.V 


ADC 

i,x 


ADC 
i,V 


STA 

i,x 


STA 

i.V 


LDA 
i , x 


LDA 
i.V 


CMP 
i,x 


CMP 
i.V 


SBC 

i,x 


SBC 
i,V 




2 


* 


* 


* 


* 


* 


* 


* 


* 


■* 


■* 


LDX 

imm 


* 


* 


* 


* 


# 




3 


* 


* 


* 


* 


■* 


* 


* 


* 


* 


* 


* 


* 


* 


* 


* 


* 




4 






BIT 
zer 


# 


* 


* 


" 




STY 
zer 


STY 
zpx 


LDY 
zer 


LDY 
zpx 


CPY 
zer 


*■ 


CPX 
zer 


* 




5 


ORA 
zer 


ORA 
zpx 


AND 
zer 


AND 
zpx 


EOR 
zer 


EOR 
zpx 


ADC 
zer 


ADC 
zpx 


STA 

zer 


STA 
zpx 


LDA 
zer 


LDA 
zpx 


CMP 
zer 


CMP 
zpx 


SBC 
zer 


SBC 
zpx 




6 


ASL 
zer 


ASL 
zpx 


ROL 
zer 


ROL 
zpx 


LSR 
zer 


LSR 
zpx 


# 


" 


STX 
zer 


STX 
zpy 


LDX 
zei 


LDX 
zpy 


DEC 
zer 


DEC 
zpx 


INC 
zer 


INC 
zpx 




7 


# 


■* 


* 


* 


* 


# 


■* 


* 


* 


■* 


* 


* 


* 


# 


* 


* 




8 


PHP 

imp 


CLC 

i m p 


PLP 
imp 


SEC 
imp 


PHA 
imp 


CLI 

imp 


PLA 
imp 


SEI 
imp 


DEY 
imp 


TYA 
imp 


TAY 
imp 


CLV 
imp 


INY 
i m p 


CLD 
imp 


INX 
imp 


SED 

imp 




9 


ORA 

imm 


ORA 
aby 


AND 

imm 


AND 
• aby 


EOR 

imm 


EOR 
aby 


ADC 

i m m 


ADC 
aby 


* 


STA 
aby 


LDA 
imm 


LDA 
aby 


CMP 
imm 


CMP 
aby 


SBC 
imm 


SBC 
aby 




A 


ASL 
ace 


* 


ROL 
ace 


* 


LSR 
ace 


* 


* 


* 


TXA 
imp 


TXS 

imp 


TAX 

imp 


TSX 

imp 


DEX 
imp 


* 


NOP 
imp 


* 




B 


* 


* 


* 




* 


* 


* 


* 


* 


* 


# 


* 


* 


■* 


* 


* 




C 


# 


■* 


BIT 
abs 


* 


JMP 
abs 


* 


JMP 
ind 


« 


STY 
abs 


* 


LDY 
abs 


LDY 
abx 


CPY 
abs 


* 


CPX 
abs 


* 




D 


ORA 
abs 


ORA 
abx 


AND 
abs 


AND 
abx 


EOR 
abs 


EOR 
abx 


ADC 
abs 


ADC 
abx 


STA 
abs 


STA 
abx 


LDA 
abs 


LDA 
abx 


CMP 
abs 


CMP 
abx 


SBC 
abs 


SBC 
abx 




E 


ASL 
abs 


ASL 
abx 


ROL 
abs 


ROL 
abx 


LSR 
abs 


LSR 
abx 


* 


* 


STX 

abs 


* 


LDX 
abs 


LDX 
aby 


DEC 
abs 


DEC 
abx 


INC 
abs 


INC 
abx 




F 


* 


* 


* 


* 


■* 


* 


■* 


■* 


■* 


■* 


■* 


■* 


■* 


# 


■* 


# 



36 










DIGITAL DATA 

RECORDERS 
USING 3M DATA 
^CARTRIDGES 



Model 3M3 
$199.95 



BRAND NEW DESIGN 

Featuring the radically new "UNIBOARD" method of construc- 
tion for data cartridge drives. The major computer manufacturers 
are changing from cassettes to cartridges at a rapid pace because of 
freedom from binding and greater data reliability. Now, these 
professional type units are priced within the range of all data users. 
Being made primarily as OEM data storage units for the world's 
major manufacturers, these units, together with controller board 
and software ROM, are being made available to the individual user 
as well. 

* Appearance and specifications may be changed slightly following 
acceptance tests now being conducted by OEM users. 




Model 3M1 
$169.95 



MODEL 3M3 - Uses the 3M Data Cartridge, model DC300. This 
cartridge contains 300 feet of .250 tape in a sealed container. 
Records and plays at 9600 baud NRZ, 4800 baud P.E. Nominal 
speed 8" per second. Max. recommended flux density 1200 fcpi. 
Using four tracks, you can store nearly 2 megabytes of data on a 
cartridge. Cartridge measures 4" by 6". Turns counter indicates tape 
position. Inter-record gap light gives more accurate position. 
2SIO(R) is not required for use, but is highly recommended for 
8080 and Z80 systems. 

COMMON SPECIFICATIONS: FULL SOFTWARE CONTROL of 
record, play, fast forward and rewind. LED indicates inter-record 
gaps. EOT and BOT are sensed and automatically shut down , 
recorder. Can also be manually operated using the switches on top 
which parallel the software control signals when not under software 
control. Signal feedback makes it possible to software search for 
inter-record gaps at high speed. 1 1 7V - 60 Hz - 5 watts. 

TWO I/O PORT CONTROLLER WITH ROM - Controls your 
terminal and one or two cassettes or cartridge units. On board ROM 
(For 8080 and Z80) has terminal and cassette software for turn on 
and go operation. NO MORE BOOTSTRAPPING. Plug in compat- 
ible with Altair and IMSAI. Loads and Dumps memory in Hex from 
the keyboard, formats tape files, punches tape, functions as a word 
processor and searches for files and four letter strings within files. 
Keyboard controls the cartridge units above on rewind and fast 
forward. Special keyboard codes enable you to dump and read 
Phase Encoded tapes as well as NRZ tapes. (Including K.C. Std.) 
Call routines give access to these from your software. 

MODEL 2SIO(R) -With 1 ROM for NRZ Cassettes $169.95 

(Assembled & Tested) ( Half of above Program) 

With 2 ROM's for Data Cartridges and 

P.E. cassettes. $1 89.95 (Full Program) 

Kits available for $30 off above prices. 

OVERSEAS: EXPORT VERSION - 220 V - 50 Hz. Write Factory 
or— Megatron KG, 801 1 Putzbrunn, Munchen, W. Germany; Nippon 
Automation 5-16-7 Shiba, Minato-Ku, Tokyo; EBASA, Enrique 
Barges, 17 Barcelona, Spain; Hobby Data, SpireaVagen 5, Malmo, 
Sweden; G.Ashbee, 1 72 I field Road, London SW 1 0-9AG. 



MODEL 3M1 - Uses the 3M Data Cartridge type DC100A. This 
cartridge contains 150 feet of .150 tape and is the same cartridge 
used by H.P. and others. Runs at 4800 baud NRZ, 2400 baud P.E. 
Tape speed adjustable, but nominally set at 5"/second. Maximum 
recommended flux density 1200 fcpi. Cartridge measures 2-1/8" by 
3-1/4". This model is ultra compact, yet extremely capable. It is 
intended for word processing, mailing list use and other applications 
requiring the compact storage of data. Data location is by 
inter-record gaps and automatic file search. See Common Specs and 
2SIO(R) below. 2SIO(R) is not required for use, but is highly 
recommended for 8080 and Z80 users. 

For 8080 and Z80 users: Comes complete with software program 
listings for the programs on the 2SIO(R) ROM below. 6800 
software is being written, but not yet completed. These programs 
give FULL SOFTWARE CONTROL. 

CARTRIDGE AVAILABILITY: Cartridges are made by 3M, ITC, 
Wabash and others. They are available at all computer supply houses 
and most major computer service centers. We can also supply them 
at normal current list prices. 

NEW: AUDIO CASSETTE INTERFACE* Phase Encoding interface 
for use with audio cassettes or NRZ recorders. Runs 2400 baud 
phase encoded on good quality audio cassette recorders. May also be 
used with 2SIO(R) above to use the 2SIO(R) cassette programs with 
your audio cassette player. Can also accommodate "Tarbell" tapes 
and K.C. Std. tapes. 

$50.00, Wired & Tested. - $35.00, Kit Form. 

*NOTE: You do not require an interface with the 3M1 and 3M3 
unless you Phase Encode. But, you do need an interface to 
use the 2SIO(R) with your own audio cassette. 

"COMPUTER AID" and "UNIBOARD" are trademarks of the 
NATIONAL MULTIPLEX CORPORATION. The 3M Data Cart- 
ridges are covered by 3M Patents and Marks. "UNIBOARD" Patents 
Pending. 

For U.P.S. delivery, add $3.00 each item. Overseas and air 
shipments charges collect. N.J. Residents add 5% Sales Tax. WRITE 
or CALL for further information. Phone Orders on Master Charge 
and BankAmericard accepted. 



NATIONAL MULTIPLEX CORPORATION 

3474 Rand Avenue, South Plainfield, NJ. 07080, Box 288 
Phone (201) 561-3600 TWX 710-997-9530 



The Digital Cassette. 



Jack Breimeir 

The Economy Co 

1901 N Walnut 

POB 25308 

Oklahoma City OK 73125 



Ira Rampil 

917 Engineering Research Bldg 
University of Wisconsin 
Madison Wl 53706 



We've now seen an illustration of the 
techniques involved in the recording and 
playback of binary strings on magnetic tape 
(in part one last month). These techniques 
are all that would be required if the cassette 
tape transport mechanism had instantaneous 
start and stop, and perfect speed regulation. 
The read and write electronics would need 
to have very wide bandwidth, as shall be 
seen later, and the tape itself would have to 
be absolutely error free. Since there are 
problems in meeting each of these require- 
ments, a great deal of effort has gone into 
data code conversion schemes that tend to 
alleviate the problems. Many different codes 
have been developed, but only a few have 
found widespread application and usage. The 
number of codes in use, in fact, is likely to 
decrease in coming years, as there are strong 
incentives in the industry to settle on stan- 
dard coding schemes which would then be 
used by everyone. There is no urgent reason, 
however, for amateurs to embrace the in- 
dustrial standard, especially if there is no 
intent to exchange tapes using the medium. 

There are several specific qualities to 
examine when selecting a coding scheme. Dr 
A E Whitehouse of the Dept of Computer 
Science, University of Manchester, in his 
doctoral thesis, selected the following seven 
characteristics inherent in each scheme to 
which relative ratings can be assigned. These 
criteria are the column headings of table 1, 
which compares a number of coding 
schemes. 

1. Bandwidth: The range of frequencies 
required to be passed by the read or 
write amplifiers for a given rate of data 
throughout should be minimal. Most 
importantly, low frequency response 
requirements should be avoided 
because 

a) low frequencies contain much noise 
like rumble, wow and flutter, and 



N 


C 


c 


> 

r 


i r 


C 

1 


i 

r 


c 

1 


i 

r 


i 




S 




























j 


u 


1 


j 


L 


j 


i 




N 






S 




J~L 


r 




1 


r 


1 


r 








L 




N 






















S 








i— i 




























































S 






















































N 




















S 
































TRACK A 






















N 




















S 






















TRACK B 










N 
















S 








































N 






















S 








i— 








1 






TRACK A 

N 












S 




L- 1 












1 






TRACK B 
















N 


n 


n 




ir 


in 




1 "1 








S 


li 


Jl 




U 


Ul 




LI 




l| 
















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i 1 i 














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J 


• 




■ 


■ 










N 








r— 






— 1 








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® 



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38 



.Subsystem: 



Part 2, 



Digital Data Formats and System Considerations 



b) difficulties in design of the read 
electronics. In general, the narrower 
the signal bandwidth, the better the 
signal to noise ratio. [Compare 
NRZ (nonreturn to zero) and PE 
(phase encoding) methods of en- 
coding as seen in figure 1 .] 
Circuit Complexity: The cost of any 
system is proportional to its com- 
plexity,. However, as can be seen in 
table 1, there are many performance 
trade-offs that improve with increasing 
complexity. 

Efficiency: The efficiency of a code is 
a measure of data density produced by 
it. Efficiency: = 100 -r (flux changes 
per bit) 



4. Inter Symbol Correlation: For the best 
performance, the codes used to repre- 
sent binary ones and zeros should be 
as different from each other as pos- 
sible. One hundred percent correlation 
occurs when the symbols used for ones 
and zeros are equal and opposite. 

5. Noise: A qualitative measure of sensi- 
tivity to tape noises such as drop outs. 

6. Read Resolution: The percentage of 
time in each bit that is allowed in 
order" to decide whether it is a one or a 
zero. 

7. Self Clocking: Does this code in- 
herently provide its own bit rate clock 
for data reconstruction? If not, an 
external clock must be provided and 



Table 1 : Comparison of magnetic media encoding formats. This is an overall chart of several different characteristics; several of 
the methods are discussed in more detail in the text. In the waveform samples, the vertical lines mark data bit times, and the 
horizontal reference line separates north from south magnetization (or vice versa). 



Code Name 


Number 

of 

Data 

Tracks 


Sample 
Wave- 
forms 


Signal 
Band- 
width 


Circuit 
Complexity 


Storage 
Efficiency 


Inter- 
symbol 
Correla- 
tion 


Noise 
Immunity 


Resolu- 
tion 


Is It 

Self 

Clocking 


Transport 

Speed 
Limitations 


Applications and Comments 


Return to zero (RZ, 
RZ pulse) 


1 


-A- 


wide 


simple 


50% 


50% 


poor 


poor 


no 


strict 


Of historical interest, not 
self erasing 


Bipolar RZ 


1 


-B- 


medium 


moderate 


50% 


1 00% 


poor 


poor 


yes 


lenient 


Of historical interest only 


Return to bias (RB) 


1 


■C- 


wide 


simple 


50% 


1 00% 


poor 


poor 


no 


strict 


Of historical interest only 


Non return to zero 
(NRZ,NRZ1,NREC) 


1 


-D- 


wide 


simple 


100% 


1 00% 


fair 


1 00% 


no 


strict 


Used on older 7 and 9 track 
commercial magnetic tape 
drives 


NRZ-mark (NRZM, 
NRZ1) 


1 


-E- 


wide 


simple 


100% 


75% 


fair 


1 00% 


no 


strict 


Used on contemporary com- 
mercial tape drives 


Complimentary NRZ 
(CNRZ) 


2 


-F- 


wide 


simple 


50% 


fair 


fair 


100% 


yes 


very 
lenient* 


Incremental recorders and 
data loggers, calculator strip 
recorders. 


Complimentary RB 
(CRB,4 phase) 


2 


-G- 


wide 


simple 


25% 


50% 


good 


good 


yes 


very 
lenient* 


Off line terminals; uses much 
tape due to low efficiency 


Pulse ratio recording 
(PR, PW, SRT) 


1 


-H- 


medium 


moderate 


33% 


good 


good 


>=50% 


yes 


tolerant of 
slow drifts 


Useful on hub driven tape 
drives (eg: Redactron) 


Phase Encoding {PE, 
split phase, Man- 
chester 11 + 180) 


1 


-[- 


narrow 


complete 


50% 


1 00% 


good 


75% 


yes 


tolerant of 
fast and 
slow change 


Currently the industry stand- 
ard for all tape systems, com- 
monly used for floppy disks. 


Manchester I 
(alsoPE) 


1 


-J- 


narrow 


complex 


50% 


1 00% 


good 


75% 


yes 


tolerant of 
fast and 
slow change 


Same as above. 



* Mote: Two channel recording methods are lenient with respect to speed variations, but have tight head skew requirements which do not exist for single channel 
recording methods. 



39 






NON RETURN TO ZERO 

\ 




PHASE ENCODED (PE) 




GOOD SIGNAL TO 
NOISE RATIO 



NRZ: 
PE: 






TYPICAL DATA WAVEFORMS 








f-l 


—II 1 III 








1 1 1 1 



Figure 1 : Frequency spectrum requirements for a practical system depend 
upon the nature of the encoding and the noise characteristics. At (a), two 
common encoding methods, non return to zero (NRZ) and phase encoded 
(PE) data are shown as a spectrum of amplitude versus frequency. NRZ 
reguires a flat response virtually from zero frequency up to the data rate, PE 
requires a frequency band response characteristic of one octave in the vicinity 
of the data rate. Looking only at the signal, and knowing electronic design 
rules of thumb such as the one that it is easier to make a narrow band 
amplifier than a wide band one, PE looks like a better method. Then, adding 
in a system noise characteristic as at (b), it becomes obvious that PE or any 
system with limited bandwidth is to be preferred over NRZ. NRZ is the 
simple method to generate (it is just a time ordered stream of data bit values), 
but its signal to noise ratio runs into problems due to noise at the low 
frequencies. 

since it is asynchronous to the data, 
this code cannot be used reliably at 
high data rates. 
For additional information beyond White- 
house's criteria, two extra columns have 
been added to table 1. 

8. Tape Transport Limitations: What re- 
quirements does this particular code 
place on tape speed accuracy and 
stability? 

9. Usual Application: These various 
coding schemes present different 
trade-off balances, and therefore have 
found themselves in a wide variety of 
different applications. A typical appli- 
cation is presented for each code. 



To efficiently analyze the entries in the 
table, it is possible to divide them into two 
groups. The division concerns the number of 
tracks required to write or recover data. 
Some codes require two channels of re- 
cording to recover one channel of data. 
These codes are, for the most part, older and 
space inefficient techniques. The advantage 
in using them is that the coding circuitry is 
relatively simple and these codes tend to be 
very speed tolerant. For the amateur, how- 
ever, the cost reduction in logic is more than 
offset by the additional cost of a two track 
tape head, an extra signal processing chan- 
nel, and the problem of intertrack head 
misalignment or head skew as illustrated in 
figure 2. Therefore, with the advent of 
quality low cost tape transports and speed 
tolerant one track codes, it is wisest to stick 
with single track recording. There is an 
exception called "mark track" recording 
which will be discussed later. There are four 
techniques which have found application 
among amateur applications. 

Non Return to Zero (NRZ) 

Conventional NRZ consists of recording a 
constant saturated level for the duration of 
the bit. For example, a string of ones input 
to the cassette will be recorded as a constant 
north magnetic level which will persist until 
a zero occurs in the input string. Obviously 
the efficiency is high; there is a maximum of 
one transition per bit, usually less. The 
possibility of long strings of either zeros or 
ones requires that the signal processing chain 
have a very wide bandwidth, extending 
down to near zero frequency. Another prob- 
lem with this system is that it is not self 
clocking, therefore an asynchronous receiver 
such as a UART must be used to convert the 
output of the tape back to synchronized 
parallel bytes. Assuming a very stable tape 
speed, both in the long term and short term, 
this technique is limited by tape noise, the 
magnetic data transfer head, and the limiting 
speed of the UART. There is a way of 
improving the reliability of asynchronous 
NRZ by making it synchronous: Recording a 
separate clock track at the data rate while 
simultaneously recording data in another 
channel provides a means of synchronously 
gating the data at playback, thus eliminating 
the need for a UART (assuming skew is not 
a problem). The National Multiplex Co of 
South Plainfield NJ provides amateur digital 
cassette recorders using NRZ or clocked 
NRZ'at up to 2400 bits per second; they 
also sell NRZ electronics boards that can be 
planted in an ordinary audio tape recorder. 
This product is capable of up to 4800 bits 
per second, depending on tape speed. 



40 









Complimentary Return to Bias (CRB) 

Complimentary return to bias is a two 
track technique which resembles the RB 
code. In RB each data cell has a binary state, 
north or south, and so in two track CRB 
each data cell is set toone of four states: 

1. Both tracks at south 

2. Track A at south, track B at north 

3. Track A at north, track B at south 

4. Both tracks at north 

State 1 represents a "no data" condition as 
in an inter record gap. States 2 and 3 
respectively represent zero and one. State 4 
is a framing signal which can be used to 
represent conditions like end of block or end 
of byte. This code is both noise and speed 
tolerant. Its clock signal can be derived from 
a simple OR of both tracks, since except in 
state 1, there are transitions every bit. This 
code, however, has poor utilization of avail- 
able tape. In other words, it is a low density 
technique and the bandwidth is even wider 
than for NRZ. As a two track technique it is 
subject to skew problems. The circuitry to 
implement CRB is a fairly simple logic 
network. 

Pulse Ratio Recording (PR) 

In the pulse ratio coding method each 
data cell uses two flux transitions in three 
possible locations. The first flux transition 
of each cell is a positive transition, from 
south to north. Its presence defines the 
beginning of the data cell and gates a clock 
on. The contents of the data cell, ie: the bit, 
is determined by the percentage of time 
spent at north as compared to south, within 
each data cell. There is a very simple method 
to decode PR by the use of a bidirectional 
counter in hardware or software. The previ- 
ously mentioned positive flux transition 
starts the counter going up. The next flux 
transition is of course a negative one. Its 
arrival switches the mode of the counter into 
down counting. The transition after that is 
the clock pulse for the next cell; it resets the 
counter and clocks out the contents of a flip 
flop which records the possible transition of 
the BORROW output of the counter - then 
the process starts over. It is the borrow 
signal which contains the data in the cell. If 
for a one bit, as in table 1, the north time 
was greater than the south time, then the 
counter result is a positive number; no 
borrow was required and the flip flop holds 
a one, the contents of the cell. A zero on 
tape has a longer south time than north 
time: The counter going into underflow 
drops the BORROW to zero for one clock 
cycle. The flip flop records the drop and 
holds a zero. This method provides excellent 



resistance to long term speed variations, 
provided the counter has enough precision. 
The bit-to-bit jitter resistance, however, is 
not so good due to the less than 50% read 
resolution. This resistance and resolution can 
be improved by accentuating the pulse width 
difference; but then noise immunity suffers 
because the bandwidth goes up. This tech- 
nique's primary advantage is that the cir- 
cuitry is the simplest for a one track self 
clocking code. 

Phase Encoding (PE) 

Phase encoding has been selected by all of 
the relevant standards organizations as the 
way to go. Most commercial manufacturers 
provide a PE option for their cassette decks 
sold to original equipment manufacturers 
(OEMs). The most widely used form of PE, 
also known as "split phase" or "Manchester 
II +180" is a single track, self clocking 
technique. The definition of the code places 
two landmarks in each data cell. The land- 
marks are actually times during a data cell 
when transitions are made in the tape 
magnetization level. The data is actually 
stored in the direction of the magnetic 
transition at the midpoint of the cell. This 
transition occurs at "data time" and is 
specified as south to north for a one, and 
north to south for a zero. In order to assure 
that the magnetic signal will be at the right 



HEAD ALIGNMENT PROBLEMS 



BUSINESS END OF 
A TAPE HEAD 



-GAP SKEW CAUSED BY LIMITA- 
TIONS IN MANUFACTURING 
ACCURACY 




GAP SKEW CAUSED BY 
TILTED HEAD MOUNTING 



Figure 2: Head alignment and manufacturing tolerances cause a phenome- 
non called gap skew in multitrack heads. At (a), the tolerances in 
manufacturing of the head itself cause one component of skew. At (b), a 
second source of skew is due to the fact that the head may not be perfectly 
mounted relative to the tape. The tilt causes a skew between otherwise 
perfectly manufactured gaps. The actual skew measured is a combination of 
both effects. The picture is exaggerated, but a small misalignment of, for 
example, 0.005 inch (0.13 mm) means a difference of 200 ms in the relative 
timing of two tracks being read at 25 inches per second (64 cm per second). 
A typical manual for a tape drive unit will warn the controller builder to put 
in circuitry to compensate for intertrack skew totalling several bits if parallel 
data is used. This skew problem argues strongly in favor of single track 
recording techniques. 



41 









Sample Circuitry for Several Different 
Coding Techniques 

This circuitry assumes that the tape deck write 
head is driven directly for output, and that tape 
input signal processing electronics produces the + 

and — flux transition clocks (low going "1 T~) 

as output. Encoding consists of preparing the 
proper signal to drive the write head from NRZ 
data, and decoding consists of converting the flux 
transition information back into NRZ data, pos- 
sibly along with clock information derived from 
the tape. 

a) NRZ coding. The output NRZ data simply 
drives the head directly. A UART or other 
asynchronous data format must be used for 
the parallel to serial conversion, and clock 
references used in writing are assumed to be 



valid within a few percent when reading the 
data back, hence the tight tolerances on 
speed. Decoding of the flux transition clocks 
is done simply by driving an RS flip flop. 

b) NRZ1 coding. The output NRZ data is 
converted to NRZ1 by using it to gate the 
clock driving a toggle flip flop (here a JK flip 
flop set up to toggle). The input flux 
transition data is converted back to NRZ by 
using the logical OR of the two transition 
clocks to drive a retriggerable oneshot with 
period (R and C) set up equal to the bit 
period. The fixed width of this oneshot also 
makes this method highly speed dependent. 

c) PE coding. The output PE data is generated 



polarity for the next data time, an additional 
transition can occur if needed at "phase 
time." Phase time occurs at the beginning of 
each data cell. The phase transition occurs at 
phase time only if the preceding bit is the 
same as the bit to be written. The phase bit 
is ignored by the read circuitry except for 
clocking purposes. In the inevitable com- 
parison of phase encoding with non return 
to zero, it first appears as though non return 
to zero provides high bit density per unit 
length of tape. True, phase encoding is less 
space efficient than non return to zero, 
requiring the time budget of two flux 
transitions per data bit compared to one flux 
change per bit. There are, however, extenu- 
ating circumstances which throw the balance 
in favor of phase encoding. The advantages 
come from phase encoding's requirement 
that each data cell have at least one flux 
change and not more than two. Thus the 
bandwidth needed for a phase encoded 
signal processing chain extends only one 
octave, from the data rate to twice the data 
rate. The bandwidth for non return to zero 
electronics extends from zero up to the data 
rate, possibly 5 to 10 octaves. The wide 
range of flux change frequencies also wreaks 
havoc on peak shift and amplitude fluctu- 
ation phenomena due to the tape itself. As 
we saw previously, peak shift and amplitude 
fluctuation cause problems in the recovery 
of raw bit strings from the tape. These 
phenomena are well defined in phase en- 
coding: Their effects are small and easily 
compensated. Self clocking is another side 
benefit of having at least one transition per 
bit. A very simple form of self clocking 
derived from phase encoding is a monostable 
set to the data rate. Triggered by each data 
transition, its output provides clock gating 
for each previous data bit. More sophisti- 
cated techniques which have great tolerance 
for tape speed variation and noise involve 



tracking oscillators or phase locked loops. 
Such systems will compensate for missing 
pulses by providing clock pulses of their own 
if the tape messes up momentarily. Phase 
encoding requires that the first byte written 
in each block be a preamble word consisting 
of 8 data transitions like the byte 01 01 01 01 . 
The preamble allows time for the phase 
locked loop to get into lock step with the 
data rate. Block diagrams for various forms 
of data encoding and recovery will be 
illustrated later. 

Since they have now appeared on the 
personal computing market, a few words are 
in order concerning GCR, Group Coded 
Recording. GCR is different from the previ- 
ously discussed codes in that here code bits 
do not bear a one to one correspondence to 
their input bits. Instead, a code converter 
ROM, like an ASCII to EBCDIC converter, 
transforms each parallel input group into a 
slightly longer output group which is then 
put on the tape. Playback involves the 
opposite process. This type of coding was 
originally developed for ultra high per- 
formance nine track drives and combines the 
best features of phase encoding and non 
return to zero. The circuitry, however, is 
very complex. 

Error Detection 

There is no easy and cheap method for 
self correcting data errors that occur on tape 
read operations. There are redundant data 
techniques which would work but at a great 
sacrifice in data throughput. On the other 
hand, there are several ways of detecting 
errors. This is almost as good as correcting 
the errors, since about 9 out of 10 errors are 
soft errors; that is to say they disappear 
upon retrying the read. Only about 1 in 10? 
to 109 bits read result in a hard, or 
permanent, error. There are also two very 



42 



from NRZ data using a clock at twice the 
data rate, and the NRZ data itself. Two 
methods are shown here, one which can be 
built from gates, and a second using an RCA 
CD4037A integrated circuit. The input de- 



coding methods can range from the simple 
oneshot method shown here to complicated 
phase lock loops which are much more error 
resistant. For the oneshot version, AT 
should be set to be 1.5 bit cells. 



(a) 



HEAD DRIVER 



NRZ O — 

FROM 

CONTROLLER 



> 



WRITE 
HEAD 



OUTPUT NRZ ENCODE 



RS FLIP FLOP 
+ FLUX I 1 

u o^-r-v n 



"LT 




r-^ NRZ TO 

^^ CONTROLLER 



INPUT NRZ DECODE 



(b) 



k5V 



NRZ _^ 

FROMO 

CONTROLLER 



X> 



DATA 
CLOCKO 

FROM 
CONTROLLER 



J 

CK 

K 



HEAD DRIVER 



^> 



OUTPUT NRZ I ENCODE 




WRITE 
HEAD 



■* c> 



.+ FLUX 



^> 



v o 



-FLUX 



I 



H 



►5V 



RETRIG6ERABLE 
ONE SHOT 



INPUT NRZ I DECODE 



(C) 



►5V . 9 



CLOCK 

AT 2XE> 

DATA 
RATE 
FROM CONTROLLER 



NRZ 
DATA 

FROM C> 

CONTROLLER 



CK 
K 



CK 
D Q 

EG:7474 



ONE BIT SHIFT 
REGISTER 
OLD 
DATA 



S> 



CK 
J 



K 

EG:7473 



new n >s 



DIFFERENCE 
DATA 



PHASE ENCODE (RANDOM LOGIC) 



: «l 



PICK ONE 



CLOCK 

AT 2XC> 

DATA RATE 

FROM CONTROLLER 

NRZ DATA 

FROM [Z> 

CONTROLLER 



tp 



CD4037A 



HEAD DRIVER 



PHASE ENCODE (RCA CD 4037A LSI LOGIC) 



+ FLUX 

^C> 

FROM READ 
ELECTRONICS 

-FLUX 

-u- O 



k5V 



7400 L_| <v 

qL— *r INHIBIT 



If 



COMBINE 






l 



AT = 



1. 5 



DATA RATE 



GATE RETRIGGERABLE^ 
ONE SHOT 



{> 






DERIVED 
CLOCK 
-(^SYNCHRONOUS 
WITH DATA 



-t>NRZ DATA 



NRZ TO 
CONTROLLER 




TO 
CONTROLLER 



RS FLIP FLOP 



INPUT PHASE ENCODED DATA DECODER 
(USING RETRIGGERABLE ONE SHOT) 



43 



1100- 



-100001 R 



IIOOOOOOOOOOOOIOI 
(CR-16 POLYNOMIAL) 
I7BITS LONG 



lino loooii 

(DATA BLOCK) 



OOOIOIIOOOOOOIIO 
(CRCC) 
16 BITS 



n BITS LONG 



Figure 3: A hypothetical cyclic redundancy check polynomial division. In a 
CRC calculation, the data is divided by a 17 bit cyclic redundancy polynomial 
to yield a result and a 16 bit remainder term. It is the remainder term which is 
used as the check word for error detection. The beauty of the whole method 
lies in the fact that it is very easy to perform the division in hardware, one bit 
at a time as the serial data goes flying by. There are even LSI circuits which 
can be used in the hardware of a controller and formatter device. 



inexpensive precautions to take to prevent 
errors: 



L Keep all tapes immaculately clean. 

Don't ever smoke in their presence. 

The smoke particulates are murder to 

magnetic tape. 
2. Always rewind tape before removing 

from the drive. This helps prevent dirt 

and crinkles from affecting the tape. 

Three methods of error detection par- 
ticularly apply to cassette operations. Only 
one method need be used at a time. The first 
technique is the commonly used parity bit. 
A parity bit is simply an extra bit tacked on 
to each byte of data. An odd parity system 
sets the parity bit to one if the one's 
complement sum of the data bits in the byte 
is equal to zero. In other words, the parity 
bit is set equal to one if there is an even 
number of one bits in the data byte. During 
a read operation, a new parity bit is gene- 



rated and compared to the parity bit written 
previously on the tape. If they are different 
there is an error somewhere. The disad- ^ 
vantage of a parity check is that it will not 
detect an error if an even number of bits in a 
single byte is wrong. Another disadvantage 
is that a parity bit per byte eats up 1 1 .1 % of 
the available room for data. For blocks 
longer than 16 bytes, there are more effi- 
cient techniques which use two bytes per 
block regardless of block length. These 
techniques are the checksum word and the 
cyclic redundancy check (CRC) word. The 
checksum technique simply sums all the data 
in the block, byte by byte, module 2. The 
resultant n bit sum is written on the tape as 
the last information in a block. During a 
read operation, the data is again check- 
summed as it enters the computer and the 
new result is compared to the sum on tape. 
Again, a mismatch indicates an error has 
occurred somewhere along the line. 

Although the theory of cyclic error codes 
is somewhat complex for discussion here, 
the following is a fairly simple explanation 
of how cyclic redundancy checks work. 
Consider any random block of data to be a 
binary polynomial of degree N, where N + 1 
is the number of data bits in the block. A 
CRC check is performed by serially dividing 
the entire data block (modulo 2) by a binary ,^ 
polynomial of degree 16. Such a polynomial 
could look like "IIOOOOOOOOOOOOIOI," 
which happens to be the standard CR-16 
polynomial otherwise represented as X^6 + 
X15 + \2 + -| § This division process is 




Photo 1: The works of a 
Phi-Deck mechanism, 
viewed from the rear. The 
four DC motors of the 
drive can be seen in this 
photo: Two are used as 
direct drive for the tape 
reels, one drives the tape 
capstan via the pully and 
belt arrangement seen, and 
the third drives a gearbox 
which actuates the tape 
head engage mechanism. 
For a view from the front, 
see photo 2. 



44 



PARITY 
SYSTEM 



PARITY 
BIT 



DATA 
BYTE 



PARITY 
BIT 



DATA 
BYTE 



TAPE MOTION 



PARITY 
BIT 



DATA 
BYTE 



PARITY 
BIT 



DATA 
BYTE 



PARITY 
BIT 



DATA 
BYTE 



PARITY 
BIT 



DATA 
BVTE 



CHECKSUM 
AND CRC 



CHECK 
WORD 



DATA BLOCK 



CHECK 
WORD 



DATA BLOCK 



Figure 4: The relationship of error detection data to data constitutes the beginning of a format for the tape data. In a parity 
system, each data byte has an extra parity bit associated with it, and blocks of data are just groups of such data and parity 
combinations between inter record gaps. In a checksum or cyclic redundancy check system, the data bytes have no detail error 
detection code associated with them and a single check word, with enough bits to guarantee error detection given the size of the 
block, suffices. Cyclic redundancy checks are easily generated in hardware, and checksums are the easier route given software as 
the means of error detection. 



illustrated in figure 3. Each unique data 
block generates a unique 16 bit remainder 
term after division. The remainder word, or 
cyclic redundancy check character (CRCC), 
is written out to tape and is compared to the 
CRCC freshly generated during a read opera- 
tion. Once again, a mismatch signifies an 
error. A CRC generator and checker can be 
implemented in either hardware or software. 
Several manufacturers such as AMI, Mo- 
torola and Signletics offer LSI chips which 
do the whole job in one package containing 
a shift register and some gates, so CRC is 
best left to hardware. CRC with the 17 bit 
polynomial is capable of detecting any num- 
ber of single bit errors and a large portion of 
any "burst" (multibit) errors that occur in a 
block less than or equal to 4096 bits long 
(for a 16 bit cyclic redundancy check code). 
CRC is fast becoming a standard for floppies 
and commercial cassette equipment due to 
its ease of generation in hardware. 

The relationships of the error detecting 
codes to the data they protect is illustrated 
in figure 4. It is important to keep in mind 
the completely serial nature of such single 
track recording. 

Tape Transport Hardware 

The choice of hardware is another place 
in which many alternatives are possible. 
Ordinary audio cassette decks have excellent 
speed regulation, but they have low tape 
speed; and included in their price are expen- 
sive audio recording and playback amplifiers 
which are not needed for digital service. In 
additional, rare is the audio deck which 
permits digital control of the mechanism. 
Most decks designed for digital service have 
good speed regulation, high tape speed, and 
.full digital control of tape motion. Their 
problem, in terms of amateurs, is price. The 
majority of digital cassette decks start in the 
vicinity of $500 for the deck itself and a 
circuit board with the motion control logic. 



Some decks provide tape transfer heads with 
preamps on the read side; some do not. Most 
manufacturers offer at additional cost a data 
encoding and decoding board. Power sup- 
plies, although usually trivial, are not cheap. 
Fortunately, there are currently available 
several inexpensive cassette decks which 
meet all of the requirements for digital 
service. One such unit is the Phi-Deck, from 
the Triple I Company, which has a current 
price tag, for the same package mentioned 
above, of between $200 and $300. The deck 
itself was originally designed for audio use in 
a language lab environment where remote 
control and good speed regulation are im- 
portant factors. With the addition of regu- 
lated high speed (up to 20 inches per 




Photo 2: Ira Rampi/'s homebrew mount for the Phi-Deck mechanism he will 
be using with his PDP-J J/ 20 system as a mass storage file subsystem. 



45 



second), the deck is fully adequate for 
digital use. Since the Phi-Deck is representa- 
tive of a large class of deck hardware and is 
itself likely to be the first choice of personal 
computing equipment designers, a few words 
could usefully be spent in a description of 
the deck. 

The Phi-Deck obtains its speed regulation 
from a tape capstan as do audio decks. Many 
other digital decks use a hub to hub drive 
technique which then requires a servo loop 
for speed regulation. The capstan is con-* 
trolled by a separate motor, as are each of 
the reels. The head is also controlled by a 
separate motor to engage and disengage it 
from the tape. A motion control board 
receives signals from the processor such as 
forward, rewind and stop. It converts these 
control signals into the proper sequence of 
voltages to control the small DC motors. The 
control board also relays back to the proc- 
essor various status lines to confirm that the 
deck is operating as instructed. The innards 
of the Super Phi-Deck are pictured in 
photo 1; photo 2 shows a Super Phi-Deck in 
a mounting designed by author Rampil for 
use in his personal PDP-11 based system. 
Figure 5 illustrates the deck in its relation- 
ship to the rest of a cassette memory system. 

Data Formatting and Applications 

Once a means of recording and recovering 
data on cassette tape is secured, some 
decisions must be made on the formatting or 
layout of data on the tape. There is a wide 
variety of possible formats. The one to select 
depends on the application. Whatever the 



application, the overall tape format should 
be as represented in figure 6: clear leader, 
blank tape, strings of recorded data sep- * 
arated by inter record gaps (IRG), blank 
tape, and finally clear trailer. Certified digi- 
tal cassette tapes and cartridges have small 
holes punched in the tape at the beginning 
and end of the usable magnetic surface. 
Essentially, the application dependent vari- 
able is the way the data is grouped on the 
tape. Grouping data into blocks is a key 
feature of most tape memory systems. 

The concept of blocking began as logical 
records being stored as separate entities on 
tape. Storing an entire program, for exam- 
ple, as a contiguous string of data separate 
from other logical records, has some merit. 
A block has clearly defined starting and end 
points, and thus eliminates word by word 
searching through an entire tape to find and 
process a particular program. As the hard- 
ware and the operating systems grew in 
sophistication, the concept of buffering was 
applied to input and output operations. 
Buffering is the process by which data from 
the outside is first read into a dedicated area 
of main memory by a monitor program, 
checked over, and then forwarded to the 
program which initially requested the data 
transfer. For example, if a program wishes to 
read some data points from the cassette 
memory, a subroutine call is placed to the 
monitor program requesting the read, the 
monitor does all the work of finding and 
reading the data, checks it for errors, and 
then relocates it to the appropriate locations 
inside the requesting program's memory 





H" 








1 

1 

1 




A 


1 

1 
t 
1 
1 


DATA 
CODING 
BOARD ■ 








8 

2 

"D 

C 
H 

m 

3J 

CD 

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to 

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R/W 
AMP 


TAPE TRANSPORT 










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COMPUTER 
NTERFACE 






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1 


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M0TIC 
CONTROL 


BOARD 



CONTROLLER 



. I 



Figure 5: An overall block diagram of a digitally controlled magnetic film memory 
subsystem. The addition of complete tape motion control and use of direct digital 
recording make such a Philips cassette subsystem a vast improvement over the 
manually oriented lower speed audio versions of tape mass storage. Functionally, 
this same block diagram applies whether the drive is for a reel to reel tape, a Philips 
cassette, a* 3M cartridge or other magnetic media. The next step up in terms of 
performance (and price) is probably a floppy disk. A floppy disk subsystem has a 
very similar arrangement, but a slightly more complicated motion control section 
needed to manipulate its movable head. 



46 



-CLEAR PLASTIC TRAILER 
/OPTIONAL EOT HOLE 



f 300 ft. 





Figure 6: The anatomy of a Philips cassette recording. A t the beginning and end of the tape is a 
clear plastic leader area. The magnetic tape (symbolized by the black area with dropped out 
lettering) has an optional EOT (end of tape) hole at each end. Data is typically grouped into 
blocks, separated by inter record gaps (IRG) which are erased regions without data. The 
content of the blocks is specified by software and hardware depending upon the particular 
system used. 



space. Although the advantages of buffering 
10 are beyond the scope of this article, it 
should be sufficient to say that they are 
important. Except in very large commercial 
machines, buffer areas are seldom large 
enough to contain an entire program as a 
single logical record. Therefore, logical 
records are often broken up into several 
smaller blocks on the tape. Not only is the 
requirement for buffer memory reduced; but 
in addition, error handling is easier. Con- 
versely, if the logical records are very small, 
for instance, one output character data, the 
buffering software collects several outputs 
together and ships it out to the tape as one 
block. The number of logical records per 
tape block is known as the blocking factor. 
Effective blocking represents a compromise 
between the smallest buffer area and the 
maximum tape utilization, ie: the minimum 
number of blocks and their associated inter 
record gaps. A graph portraying the approxi- 
mate relationship between the length of data 
blocks, assuming they are all the same fixed 
length, and the total data capacity of a C-30 
cassette is presented in figure 7. 

The simplest application lends itself to 
the simplest formatting. A digitally con- 
trolled cassette system or manually con- 
trolled system may be used as an inexpensive 
substitute for a high speed paper tape reader 
punch. In fact, several manufacturers offer 
cassette systems that are plug compatible 
with paper tape equipment. The data is 
blocked byte by byte, or not at all. Since 
there is no file structure, the data appears on 
the cassette exactly as it would on paper 
tape. There is no need for inter record gaps 
between bytes in this format, for by placing 
very long gaps between logical records on 
the order of a foot or two of tape a human 
operator can locate a particular logical re- 



cord with the aid of a tape counter mech- 
anism, just as an audiophile would find a 
particular song. A UART is a very neat way 
to generate the parallel-serial data conversion 
for this byte oriented format. The disad- 
vantage of using a UART here is that it adds 
at least three extra bits, start, stop and 
parity, to every byte thus reducing the data 
density on the tape. 

For more efficient and useful operation, a 
file structure should be added to the digi- 



\- 

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en 

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400K 


ASSUMING SINGLE TRACK RE. 
(cD BOOBPI (I600FCI) 






300K 


- 






200K 








IOOK 


i 


l 


\ r 




10 


100 


1000 



CHARACTERS (BYTES) PER BLOCK 

Figure 7: Cassette capacity versus block size. The inter record gap (IRG) is 
essentially wasted space on the tape. By increasing the size of the block, the 
percentage of tape wasted on IRGs declines toward a limit of zero. As the size 
of the block is decreased (ultimately to its limit of a single byte separated by 
IRGs on either side) the total number of bytes available on a tape declines. 
For any given set of parameters (inter record gap length in inches, flux 
density in bits per inch, and data format), the total useful data per cassette 
can be calculated and plotted as one point on a curve such as this. 



47 












tally controlled transport. By blocking the 
data Into chunks of convenient size with 
identification information, software can then 
examine each buffer as it is read in to search 
for any particular file (a group of such 
blocks) on the tape. A file is considered to 
be a single logical record even though it 
might cover many blocks. In a file structured 
system with a remotely controlled tape 
deck, keyboard commands or commands 
generated by a program replace manual 
intervention and the automatic operations 
make the system much more convenient. 
Still lacking, however, is a very useful block 
replacability feature since there is no way to 
synchronize the start of overwriting with the 



FOR FURTHER READING 

Books 

Bycer B B, Digital Magnetic Tape Recording: 
Principles and Computer Applications, Hayden 
Co, NY 1965. This book has an excellent 
introduction to the theory, but the chapters on 
applications are heavily dated. 

Sebestyn, L G, Digital Magnetic Tape Recording 
for Computer Applications, Chapman and Hall 
Ltd, London, 1973, an unimposing but very 
usable modern reference; a book shelf must for 
the designer types. 

Commercial Literature 

1. Memodyne Corp, Newton Upper Falls MA, 
"Recording Binary Code on the Philips Cas- 
sette," an 1 1 page brochure. 

2. MFE Computer Access Systems, Salem NH, 
"Applications Notes #63 to 66" a pro and con 
discussion of cassette decks and recording 
techniques. 

3. Motorola, Mesa AZ: 

a) "M6800 Microprocessor Applications Man- 
ual," includes the complete design of a 
possible cassette memory system including 
software. 

b) "Phase Locked Loop Manual," discussion of 
using PLLs for PE decoding. 

c) "MC3467, MC3468 Applications Notes," 
monolithic magnetic tape read chains. 

d) "MC4044 Applications Notes," using a PLL 
phase detector in PE decoding. 

e) "MC8521 Preliminary Data Sheet," not yet 
released, but a complete PE decoder on a 
chip. 

4. RCA, COS/MOS Data Book, "Applications 
Note ICAN6101, ICAN6210," PE decode/ 
encode using CMOS. 

Acknowledgements 

The authors would like to thank the following 
individuals and groups for their gracious generosity 
and assistance: 

Joe Roy, Motorola 

Paul Nordeng and the DASL Staff, University of 
Wisconsin 

The Economy Company. 



beginning of a data block, especially if the 
drive has stopped in the preceding gap. 
Although it is not possible in this system to -^ 
overlay a corrected or updated program into 
the space it formerly occupied, it can easily 
be added on to the end of the tape. 

Musings on the Ultimate 

The ultimate cassette memory system 
incorporates block replaceability and sector 
addressing to simulate random access stor- 
age. The technique proposed here for Phi- 
Decks is similar to that used so successfully 
by Digital Equipment Corporation in their 
DECtape units. I n fact the Sykes Corporation 
developed and marketed such a system for 
cassettes until their attentions turned to 
floppy disks. The trick is use one track for 
normal phase encoded or pulse ratio data 
and a second track as a prewritten mark 
track. The mark track is first written to 
initialize the tape and it is only read there- 
after. It contains, in the same code as the 
data track, various sorts of delineators, or 
marks, and also the block address numbers 
of the data blocks residing on the adjacent 
data track(s). Data is written in fixed sized 
blocks in synchronization with the areas 
designated by the mark track. By observing 
the transitions on the mark track, the tape 
controller will have no difficulty in over- 
laying or replacing previously written data. 
The advantage of including block numbers 
on the mark track is that as they are read in, 
they can easily be compared with a register 
containing a block number being sought, 
thus eliminating the need for a software 
search program. Usually a directory data 
block is included on the tape, most fre- 
quently as the first data block. Its contents 
generally include the file names and their 
starting block addresses. When a cassette is 
first mounted in the drive, its directory is 
read in. Whenever the computer needs access 
to a tape file, it gets the block address from 
the directory and initiates a hardware search. 
Each time a change is made to the tape, the 
directory copy in memory is updated and a 
copy of it is written back to the tape. Using 
one's imagination, many different file 
manipulations are possible with such a sys- 
tem. Anything possible with a floppy disk 
operating system is in fact possible with a 
mark track cassette system. The tradeoff is 
just time versus price. A floppy is essentially 
instantaneous, from a human standpoint. A 
cassette system takes from seconds to a few 
minutes, at about one fourth the price of a -^ 
floppy. Even with these time constraints, a \ 
full digital cassette system is a lot less 
painful than Teletype paper tape or audio 
cassette." 



48 



. 












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What's Involved 
in Kit Building? 



i~mi iiHrifff 



A collection of typical 
tools useful in building a — * 
kit. This collection in- 
cludes several sizes and 
types of screwdrivers, 
needle nose pliers, side 
cutter (diagonals), a set of 
nut drivers, pliers, wire 
stripper, knife, soldering 
iron and solder. A solder 
removal device, such as a 
bulb sucker or a mechani- 
cal action sucker, is also 
most useful. 



Louis E Frenzel 

1588 Oak Ter 

St Joseph Ml 49085 



Most of the personal computing equip- 
ment available to the hobbyist today is in kit 
form. As a result, the field of personal 
computing as it is now known essentially 
centers around the building, testing and 
troubleshooting of computer kits. Many 
individuals with a "computer hobbyist" 
approach to the field are electronic types 
who enjoy kit building and consider their 
work with the equipment to be the main 
focus of their interests. 

However, many other people would 
rather concentrate on the programming and 
application of the equipment. Such in- 
dividuals may not enjoy or even consider 
themselves capable of building some of the 
sophisticated computer kits available. Yet 



many of these nonhardware types are taking 
a chance on their being able to successfully 
learn kit building. They do so simply to be 
able to have the equipment that is available 
today. At this point in the development of 
the personal use computer field, being able 
to build a kit often means the difference 
between being able to own a fairly sophisti- 
cated computer or not. 

There are many benefits to be gained by 
building a kit. Kit building is something that 
can be learned and easily mastered even by 
individuals who do not know and under- >^^ 
stand electronics. The purpose of this article } 
is to outline the benefits of kit building and 
to present some basic guidelines and pro- 
cedures that anyone can learn to successfully 






50 






Kit building is something that can be learned and 
easily mastered even by individuals who do not know 
and understand electronics . . . 



construct a kit. The personal use computer 
field will continue to remain essentially a kit 
business for the immediate future. Why not 
join others in experiencing the benefits that 
come from this activity? 

Benefits of Kit Building 

Most inexpensive computer equipment is 
available in kit form because sometimes this 
is the fastest and easiest way for a manu- 
facturer to develop and offer the product. 
This has allowed many small companies to 
enter the market quickly. Kits have been 
largely responsible for expediting the growth 
of hobby and personal computing by allow- 
ing young manufacturers to sell more 
products sooner. 

While kits offer benefits to the manu- 
facturer and to the builder overall, the real 
benefits of kit building go to the builder. 
Some of the benefits are obvious, but others 
are more subtle. Let's consider them. 

Save money. One of the obvious benefits 
of purchasing kit equipment is the resulting 
savings in money. Kits almost always cost 
less than equivalent wired and tested prod- 
ucts simply because the cost of labor is 
removed. In some cases, the price of a kit 
can be as low as one half the assembled 
price. Such savings are significant and have 
often made the difference between an in- 
dividual being able to afford a computer or 
not. The cost savings has further benefited 
the field by allowing many more individuals 
to participate. It certainly makes sense to 
assemble the equipment yourself if you can. 
For a given upper limit dollar investment, 
you can afford significantly more equipment 
if you purchase kits. 



Pride of accomplishment. A benefit not 
as obvious to those who have never built a 
kit is the sense of achievement that it 
produces. This is particularly true of large, 
complex and difficult kits. When an in- 
dividual successfully assembles a sophisti- 
cated kit and makes it work, he or she is 
rewarded with a real sense of accomplish- 
ment. This is a feeling that is hard to 
describe, but one that becomes obvious 
when you build your first successful kit. 

Fun and enjoyment. This is a do it 
yourself age. Most people enjoy doing things 
for themselves if they can. There is a certain 
amount of enjoyment in tuning your own 
car, growing your own garden, or paneling 
your basement. The same is true in the 
computer field. People want to do it them- 
selves and find enjoyment in it. Kit building 
as a hobby fulfills this need for fun and 
involvement. Like other hobbies, kit build- 
ing is relaxing since you become occupied in 
an activity that demands your full attention 
and skill. It takes your mind off other 
problems and worries. 

Learning. One of the most subtle benefits 
of kit building is learning. Whenever you put 
a kit together and make it work, you 
automatically learn more than you realize. 
The whole process of kit building is educa- 
tional. This is particuarly true for those 
individuals who are not electronic experts. 
Beginners quickly learn basic skills such as 
soldering, identifying electronic com- 
ponents, theory of operation and basic 
testing and troubleshooting methods. The 
learning may not be obvious as you are 
constructing the kit, but it is there and 
sooner or later you will realize it. 



Kits can: save money, give 
pride of accomplishment, 
provide fun, enjoyment 
and learning, and prepare 
the owner for maintenance. 




r 



Lou Frenzel has been an enthusiastic personal computing advocate of the 
"build it yourself" variety for some time. His personal systems presently 
include an I MSA I 8080 kit product with 8 K of memory, an evaluation board 
6800 system from Motorola with enough additional memory to run Tom 
Pitt man's Tiny BASIC, an ASR 33 Teletype, audio cassette interfaces, serial 
and parallel interfaces for custom peripherals. One projected application for 
the computers is to amateur radio, where he aims to use the processors for 
station control, and processing of message and fogging data for his station, 
W8LJR. Professionally, Lou is Director of Computer Products for the Heath 
Company, a firm which started the electronics kit business as it is known 
today. 



51 









A "beginner's" kit assumes 
no knowledge of elec- 
tronics and is exhaustively 
documented. 



An "experienced builder's" 
kit assumes some knowl- 
edge and familiarity with 
electronics and as a result 
is less expensive due to 
savings in documentation 
cost. 



Preparation for maintenance. Electronic 
equipment is much easier to service, repair 
or modify if you are familiar with it. Once 
computer equipment has been assembled 
and made operable, it is generally reliable. 
But should service be required, it will be 
easier if you know and understand the 
equipment. Kit building gives you much of 
that knowledge and familiarity. 

These are only a few of the most im- 
portant benefits of kit building. If you want 
total involvement from your use of com- 
puters, you should participate in as many of 
the different facets of it as you can. Kit 
building is one of the best ways of achieving 
this participation. 

Types of Kits 

All kits are not equal. There are big kits 
and little kits, easy kits and complex kits. In 
addition, there are different types of kits 
depending on the approach taken by the 
manufacturer and the intended customer. 
Before you purchase a kit and attempt to 
assemble it, it is a good idea to be aware of 
the types of kits available. 

There are two broad, general classifica- 
tions of electronic kits, those for beginners 
and those for experienced hardware people. 
These classifications really represent the 
extremes of a range of types of kits; but for 
purposes of discussion such "ideal types" are 
useful. Kits designed for the beginner are 
generally simpler and more thoroughly docu- 
mented. Even an individual who knows 
nothing about electronics can usually 
assemble such kits successfully. The assem- 
bly, test and troubleshooting instructions are 
thorough, take nothing for granted and lead 
the kit builder by the hand through a step 
by step process of assembly. With such a kit, 
most people have little or no difficulty in 
assembling the product and getting it to 
work regardless of their knowledge and 
experience. Even though you may not be a 
beginner, this type of kit is often the best in 
terms of value because it practically insures 
hassle free building and a workable end 
product. 

Another type of kit is one designed for 
the experienced kit builder or electronics 
expert. Such kits are furnished with a 
minimum of documentation and assembly 
instructions. In some cases only a schematic 
diagram, a printed circuit board layout 
showing component placement, and a parts 
list are supplied. To an experienced builder, 
this is usually sufficient information to 
assemble the product and get it to work 
properly. Many of the computer hobby kits 
available today are of this type. They assume 
that the builder is familiar with such equip- 



ment or it would not be purchased in the 
first place. Many novices and beginners have 
discovered this too late. There's nothing ^ 
wrong with this type of kit because it does 
produce a useable end product. The problem 
comes when an inexperienced builder at- 
tempts to construct a kit of this kind and 
makes mistakes due to either lack of knowl- 
edge or experience. Such kits are highly 
desired by the experienced builder because 
they give him far greater satisfaction and a 
feeling of more involvement than the simpler 
kits, and ultimately have a lower cost since 
"idiot proofing" the documentation is a 
significant cost item in any kit. Experienced 
electronic kit builders receive great satisfac- 
tion from using their knowledge and experi- 
ence in such projects. Many even enjoy 
discovering errors or having to supply miss- 
ing information. They like to do the research 
necessary to build a product successfully. 
What may be a problem and big frustration 
to some is a real challenge and enjoyment to 
others. 

Qualities of a Good Kit 

Just what are the qualities of a good kit? 
It is desirable to know the elements of a 
good kit so that when you evaluate a 
product or compare competitive units, you ^^ 
will choose the best product for you. Here 
are several things you should look for in 
choosing a kit product. 

Well designed. This is a subjective point 
yet an important one. A good design is one 
that works, has proven itself reliable and 
accomplishes its purpose. Other elements of 
good design involve the use of modern 
components and techniques. Good design is 
difficult to assess if you are not familiar with 
the specifics of the equipment or the latest 
technology. However, good product design 
generally shows up as a good reputation in 
the field, positive comments from owners, 
and favorable magazine test reports. If you 
are a newcomer, read every scrap of literature 
you can find, talk to people at your local 
computer club, and keep an open mind! 

Good documentation. Just as important 
as good design is good documentation. This 
is an absolute necessity for a successful kit. 
The manufacturer simply must supply suf- 
ficient information to build, test and apply 
the product. Poor documentation usually 
means the difference between a good kit and 
a bad kit. A well designed kit can be bad 
because poor documentation makes it diffi- 
cult if not impossible to assemble and use. >— k 
Look for and insist upon good documenta- 
tion to the level of detail you require. 

Quality components. Quality or first 
grade components are a major part of any 



52 



Some Typical Introductory Kits 

The Heath Company is the oldest and largest manufacturer of kits. For those computer people who are wary of trying a 
complicated kit, author Frenzel suggests several of his company's products as a means of seeing what it takes to build a kit by 
trying out the concept on simple items. Each of these items will result in a useful accessory for the computer lab, as well as 
introducing the builder to the process of building kits. 




a. A prototyping breadboard. In computer 
applications, such a breadboard can be used 
to temporarily try out a circuit before com- 
mitting it to permanent form using wires, 
sockets, Vectorboard and solder or wire 
wrap. Power supplies at standard logic (+5 V) 
and typical analog (±12 V) levels aid proto- 
typing with this unit. 



good kit. If a manufacturer uses regular 
commercial grade components, then the 
quality is good. Quality components help 
insure reliability and a minimum of defects 
and problems in assembly. Kit suppliers can 
sometimes purchase surplus or degraded 
components at significant savings. As a result 
they can pass along major cost savings to 
you. While lower cost is certainly a signifi- 
cant benefit, it is often offset by the 
problems encountered by the poor com- 
ponent quality. Unless you are prepared to 
deal with the limitations and problems 
brought about by low quality components, 
it is best to stick with the higher priced but 
more reliable units using quality parts. 

Designed as a kit. Many products are not 
designed to be kits. Such products are 
designed first to have specific features and to 
meet certain performance specifications. The 
fact that it is to be offered in kit form is 
often secondary. The designer's main pur- 
pose is to achieve a saleable and workable 
product. Once this has been done, many 
designers feel that it is only necessary to 
supply the components in a bag which the 
.customer can assemble. If the product is 
designed as a kit, the designer is constantly 
reminded that the product must be easy to 
assemble and service. For that reason, kit 
design and thorough documentation is some- 




b. A laboratory bench power supply. Once 
built, this instrument is used to simulta- 
neously power logic (+5 V) and provide 
variable metered analog levels from ±0 to 
±20 V. 




c. A multimeter. This all around useful test 
instrument can be built from a kit and later 
used to measure miscellaneous voltages, cur- 
rent and resistance when diagnosing or 
using the hardware of a computer and its 
interfaces. 



what more difficult and time consuming 
than designing equipment that will be manu- 
factured. Such products generally come 
from those manufacturers dedicated to the 
kit business. 

Manufacturer support. A good kit manu- 
facturer is one that supplies plenty of service 
and support. A customer can make wiring 
errors, receive a defective component or 
simply have difficulty in interpreting the 
documentation. The customer must have 
some way of dealing with these problems if 
he or she is to be satisfied with the product 
and complete its assembly. Always look for 
a kit manufacturer which has a significant 
amount of backup. This means the manu- 
facturer will answer your letters and tele- 
phone calls regarding problems. In addition, 
the manufacturer should offer complete 
service and repair facilitiies at reasonable 
prices. Also check the warranty. Before you 
purchase a kit, be sure that you satisfy your 
own requirements with regard to the support 
and service available. 

These are the main qualities of a good kit. 
Before spending hundreds or even thousands 
of dollars on computer equipment, investi- 
gate these points carefully. Your satisfaction 
with the products will be greater if you do. 



A good design is one that 
works, has proven itself 
reliable, and accomplishes 
its purpose. 



53 













Key 1: A low wattage 
soldering iron is a must for 
building computer kits (or 
any kit with delicate 
printed circuit runs). Here 
is a typical low wattage 
iron with a small tip, along 
with a suction bulb device 
which can be used to 
remove solder if necessary. 






Photo supplied by the Heath Company 



Read test reports on the products that you 
are considering. Ask friends, associates and 
fellow club members for their opinions on 
the product. Often the experiences of others 
can help you decide. Also get as much 
information from the manufacturer as you 
can. If the data sheets and catalogs supplied 
are insufficient, write for further informa- 
tion. A reputable manufacturer will answer 
your specific questions and provide addi- 
tional information as required. 

One of the best ways to size up a product 
is to purchase the documentation for the kit. 
Most manufacturers will allow you to pur- 
chase the assembly and operation manuals. 
This will give you full details on the product 
and will give you an advanced look at the 
assembly instructions and other information. 
If you're serious about a product, this is a 
small investment to make to insure that you 
obtain a good product. 

Building the Kit 

Here arc some tips, based on experience, 
that can help you build kits successfully 
even if you are a beginner: 

Practice first. Before you wade into a 
$1000 computer kit, perhaps you should 
test or improve your skills first on a simple, 
low cost kit. This is particularly true if you 
are a novice. If you have never assembled a 
kit before, start out with a small, easy to 
build project first. You will learn a lot by 
assembling this simple project first, and you 
will get a feel for what kit building is all 
about. 



There are a wide variety of simple low 
cost kits available. Many accessories and 
pieces of test equipment fall into this 
category. Try to choose a project that will 
be useful to you when you get to the 
computer kit, or in some other way. A good 
example of equipment that could be of value 
to you when working with computers is a 
volt ohmmeter or a power supply. Both of 
these items are relatively easy to build and 
you will find much use for them later when 
working with your computer system. 

Obtain the proper tools. You will need a 
variety of tools to build a kit successfully. 
There is nothing more aggravating than to 
come to a point in the assembly process 
where you do not have the tools needed. 
While most kits can be assembled with 
common tools, you should provide yourself 
with a minimum set prior to building your 
kit. It will make the kit building process go 
faster and easier. Here is a list of the most 
common tools you will need: 



I. 


screwdrivers of several sizes: blade and 




Phillips types 


2. 


needle nose pliers 


3. 


side cutters 


4. 


nut drivers (0.25 inch is the most 




useful.) 


5. 


pliers 


6. 


wire strippers 


7. 


knife 


8. 


soldering iron 


9. 


solder 


0. 


solder removal device 



Learn to solder. The most important skill 
required to build a kit is soldering. The 
majority of computer equipment is con- 
structed by attaching electronic components 
to printed circuit boards. The circuit boards 
are then interconnected to one another 
through other printed circuit boards, con- 
nectors and cables. Solder is the common 
bonding element in all cases. You simply 
must learn to solder if the kit is to work 
properly. 

Soldering is the process of melting an 
alloy of tin and lead known as solder, 
wetting the component leads with the hot 
molten solder, then allowing it to cool and 
provide a permanent electrical interconnec- 
tion. The components to be joined are 
brought together physically and the joint 
made mechanically secure. Then a soldering 
iron is touched to the joint so that the 
component leads are heated. Once the joint 
is hot enough, solder is applied and allowed 
to flow over the connection. Then the heat 
is removed and the solder is allowed to 
harden. The result is an excellent mechanical 
and electrical connection. 



54 



To solder properly, you must have the 
right equipment. Primarily this means a 
soldering iron and solder. For most elec- 
tronic construction, a small, low wattage, 
hand held pencil type soldering iron should 
be used. One with a wattage rating of 25 to 
40 watts is best. This will provide more than 
sufficient heat but at the same time is low 
enough in wattage to prevent damage to 
electronic components. The soldering iron 
should also have a small, fine tip so that 
solder can be successfully applied to the very 
small connection pads on most computer 
circuit boards. 

The type of solder used is also important. 
Many kits are supplied with the proper 
solder. If solder is supplied, use it. If you 
buy your own, be sure to purchase quality 
electronic grade solder. The best is a 60-40 
rosin core solder. The 60-40 refers to the 
percentages of tin and lead respectively in 
the solder. The rosin core means that the 
solder contains a cleaning element that helps 
to remove the oxidation from the connec- 
tions when heat is applied. (Do not use acid 
core solder which can destroy electronic 
components. It will literally digest your 
computer.) 

The size of the solder is also important. 
For the tiny circuit board work found in 
most computer products, a thin solder is 
best as it is easier to control the rate of flow. 
Solder smaller than 0.032 inches in diameter 
is best. This will prevent excess solder from 



being applied and will reduce the possibility 
of making solder bridges. 

Next you should develop your soldering 
skills. The best way to do this is to practice. 
The proper procedure is to first physically 
connect the components. Usually this in- 
volves bending the leads of the component 
and mounting it on a printed circuit board. 
The soldering iron is then used to heat the 
junction of the component lead and the foil 
on the printed circuit board. It takes only 
several seconds for the joint to become hot 
enough to melt solder. Solder is then applied 
to the junction and allowed to flow over the 
leads and copper foil. The solder and iron 
are removed and the connection is allowed 
to cool and harden. 

While the procedure sounds simple, it is a 
bit subtle. The subtlety has to do with the 
amount of time you heat the junction prior 
to applying solder and the amount of time 
the iron is left on the joint after solder is 
removed. If you apply too much heat in the 
beginning you can damage the component or 
cause the copper foil on the printed circuit 
board to peel off. Yet if you do not apply 
enough heat, the joint will not become 
sufficiently hot to melt the solder properly. 
If the solder is not melted thoroughly it will 
cause a so called "cold solder" joint. These 
are conditions where proper bonding does 
not take place. The amount of time that the 
heat is applied is a balance between that 
which prevents damage and that which 




Simple points: Practice 
first, obtain proper tools, 
learn how to solder, learn 
how to unsolder, and if all 
else fails, read the 
directions. 



One of the best ways to 
size up a computer prod- 
uct is to purchase the 
documentation (or borrow 
it from a friend). This is 
true whether the product 
is in kit form or not. (A 
corollary is the thought 
that good looking and 
complete documentation is 
an excellent sales tool for 
the manufacturer.) 



Key 2: One key to good 
soldering is a clean solder- 
ing tip. There are several 
different brands of wet 
sponges like this one, 
which can be used to clean 
the tip during use. Many 
of these products are 
treated with special chem- 
icals to help improve the 
cleaning properties. 

Photo supplied by the 
Heath Company 



55 






allows the solder to melt and flow as it 
should. The skill and timing in this operation 
comes only from practice. 

Learn unsoldering. Another skill practi- 
cally as important as soldering is un- 
soldering. It is often necessary to remove a 
component from a printed circuit board. 
The component may become defective and 
need replacing. Or you may have discovered 
that you connected the component incor- 
rectly. If you learn the technique of un- 
soldering, the component can be removed 
without damaging it or the printed circuit 
board. 

Unsoldering is best accomplished by re- 
moving the solder on the connection. Do not 
attempt to remove a component by simply 
reheating the connection and prying the 
component from the printed circuit board. 
Damage will usually result. Although it takes 
a little more time and care, removal of the 
solder first will insure that you do not 



Key 3: Use proper solder- 
ing technique. This set of 
illustrations provided from 
the Heath Company docu- 
mentation of kits illus- 
trates proper soldering 
technique when assem- 
bling circuit boards. As 
noted at the bottom, it is 
important to heat both the 
component lead and the 
printed circuit board con- 
tact. If either is missed, 
then a bad joint as at B or 
C could result. 



damage either the component or the printed 
circuit board. 

Solder can be removed from the connec- 
tion by first heating the connection with 
your soldering iron and and then using a 
suction bulb. This is a device designed to 
pull the solder from the connection by a 
vacuum created in a rubber bulb. A plunger 
type device known as a solder sucker can 
also be used. 

It may take several applications of the 
tool to remove all of the solder. Get as much 
off the connection as you can. Then use a 
knife or needle nose pliers to carefully break 
the component lead loose. 

Another method of removing solder from 
a connection is to use a wire braid coated 
with rosin. The braided wire is coarse and 



1. Place the soldering iron tip 
against both the lead and the 
circuit board foil. Heat both 
for 2 or 3 seconds. 



COMPONENT 
LEAD- 




CIRCUIT BOARD 



2. Then apply solder to the other 
side of the connection. 
IMPORTANT: Let the heated 
lead and the circuit board foil 
melt the solder. 



SOLDERINGy 

SOLDER 'RON, 




3. As the solder begins to melt, 
allow it to flow around the 
connection. Then remove the 
solder and the iron end let the 
connection cool. 



SOLDERING 
IRON 




4. Hold the lead with one hand while you cut off the excess lead 
length close to the connection. This will keep you from being hit 
in the eye by the flying lead. 



Be sure the solder made a good electrical connection. 

When both the lead and the circuit board foil are 
heated at the same time, the solder will flow onto the 
lead and the foil evenly. See Illustration A. The solder 
will then make a good electrical connection between 
the lead and the foil. 

When the lead is not heated sufficiently, the solder 
will not flow onto the lead as shown at B. Reheat the 
connection and, if necessary, apply a small amount of 
additional solder to obtain a good connection as 
shown at A. 

When the foil is not heated sufficiently, the solder 
will blob on the circuit board as shown at C. Reheat 
the connection and, if necessary, apply a small 
amount of additional solder to obtain a good connec- 
tion as shown at A. 



SOLDEK FLOWS OUTWARD 
AND GRADUALLY BLENDS 
WITH THE FOIL AND THE 



® 



£» 



,'< 



SOLDERING 

IRON 

POSITIONED 

CORRECTLY 



SOLDER DOES NOT FLOW 
ONTO LEAD A »ARK ROSIN 
BEAD SURROUNDS AND IN- 
SULATES THE LEAD FROM 
THE CONNECT ION 

FOIL 



IURNED / / 
ROSIN /i ' 

/ / / SOLDERING 
/ ' '/\ IRON 
*•'" POSITIONED 

&' INC ORRECTLY 



..■'.v. \\\\\ 



SOLOER APPEARS TO FLOW 
INWARD AND SjJ ON TOP 
OF THE FOIL. I 



© 



' SOLDERING 
*\ IRON 
POSITIONED 
INCORRECTLY 



^fK BURNEO 
X X^ROSIN 



h 



.;■;■:;.;:;■:-::■■:■' ;cz 



56 



can soak up a lot of solder. The rosin cleans 
the braid and the connection and encourages 
the capillary action that literally slurps the 
solder off the connection. To use the braid 
you simply place it on the connection and 
heat it with the soldering iron. The solder 
will flow up into the braid leaving the 
connection clean and open. Again, several 
applications may be necessary to remove all 
of the solder. Solder removal braid is avail- 
able at most stores selling soldering irons and 
related equipment. It is extremely effective 
and will save you much time and possibly 
some expensive components and printed 
circuit boards. 

Follow directions. It seems almost ridicu- 
lous to point this out, but one of the most 
common faults of kit builders is not follow- 
ing the assembly instructions. The assembly 
instructions have usually been tested to 
insure that they work. If you use a different 
assembly sequence or fail to note some of 
the special instructions, you are most likely 
to make a mistake. Even though you may be 



an experienced kit builder, sometimes there 
are subtleties in the assembly process that 
make it absolutely essential that you follow 
the given directions. 

Another precaution is to look for any 
errata sheets or correction notices before 
you begin the assembly. Some errata sheets 
are included randomly or at the end of the 
supplied documentation. Don't take 
chances; catch the errors in the documenta- 
tion first to avoid mistakes. 

Don't ruin your investment by assuming 
that you can do it by yourself. Protect your 
investment and follow the instructions. Re- 
member the old saying, "If all else fails, read 
the instruction manual," is true. 

Take your time. When building a kit, take 
your time. The faster you go the more likely 
you are to make a mistake. Most people who 
purchase kits are anxious to put them 
together and use them. This is only human 
and certainly understandable. But unless you 
have patience and take your time to follow 
the instructions and do quality work, your 



Use of sockets remains a 
highly recommended prac- 
tice — but use quality 
sockets by all means. 



Key 4: If you make a mistake, fix it. To remove solder, use a bulb sucker (see key I ), a mechanical solder sucker tool (a), or a 
solder removal braid (b). 



(a) Photo supplied by the 
Heath Company 



(b) Photo courtesy of Wik-lt 



I 




57 



(a) 



Key 5: A detailed solder 
braid removal sequence, 
supplied by Wik-lt. (a) 
Find the connection to be 
desoldered. (b) Heat the 
connection through the 
braid, causing capillary 
action to suck up the 
solder, (c) Remove solder- 
ing iron and braid, to view 
the desoldered connection. 



(b) 





(c) 




chance of achieving a successful build are 
much lower. A better end product will result 
if you take care and time. 

Part of the concept of taking your time is 
to spread the kit building process out over a 
long period. It is a lot better to have eight 
one hour or four two hour kit building 
sessions than it is to have a single eight hour 
session. The longer the kit building session, 
the more mistakes you are likely to make. 
When you find yourself getting tired, losing 
interest, or attempting to short cut the 
instructions, stop. Go back to building when 
you have had a chance to rest. 

While it's good to take your time in 
building a kit, just keep in mind that most 
kits come with a limited time warranty. 
Thirty and ninety day warranties are typical, 
so it is highly desirable that you assemble 
the kit in less than that time. If you discover 
any defective parts or other problems, you 
can get them replaced within the warranty 
period. Take your time, but don't lose the 
benefit of any warranty that you may 
receive. 

Ask questions. As you Ye building a kit 
you may have questions about the assembly. 
If the instructions are not clear or problems 
arise, don't guess. Don't take anything for 
granted. Attempt to answer the question 
yourself, of course. Study the directions 
more carefully. Ask a friend who has built a 
similar product. Call or write the manu- 
facturer to be sure of what you're supposed 
to do before you go on. You can save a lot 
of time, money, grief and dissatisfaction if 
you get answers to questions before going 
ahead with what may be an incorrect 
decision. 

Use sockets. Many electronic kits do not 
supply sockets for the various components. 
Transistors, diodes and integrated circuits 
are usually soldered directly to the printed 
circuit board. Some of the more expensive 
and delicate components may use sockets. 
While sockets may not be supplied, it is 
generally a good idea to add them yourself. 
The sockets will allow you to remove com- 
ponents for troubleshooting purposes or to 
replace them if they become defective. The 
socket will add a little extra cost to your kit, 
but the advantages are worth it. The ease 
with which a product can be serviced when 
all of the integrated circuits are in sockets is 
excellent. It is one investment that you may 
question in the beginning but will certainly 
find worthwhile later should you have dif- 
ficulty. If you choose to use sockets, how- 
ever, be sure to use high quality new sockets, 
preferably with gold or other nontarnishing 
finish on the contacts. 

Provide yourself with reference resources. 



58 






Many manufacturers supply all the informa- 
tion needed to construct the kit successfully. 
k Additional information simply is not neces- 
sary. But there are some kits that require 
you to have additional information. For 
example, it may be necessary for you to 
know the pinouts or theory of operation of 
the various TTL or MOS integrated circuits 
used in the kit. Because of this, it is a good 
idea to provide yourself with a reference 
library of books, catalogs, data sheets and 
any other information you can get your 
hands on. You will also find general text- 
books and application notes from the inte- 
grated circuit manufacturers to be helpful. 
When you run into trouble or have ques- 
tions, your references can provide the 
answers. It is an excellent investment that 
you should make at the time that you 
purchase your kit. 

Two of the most important references 
you should have are the Texas Instruments 
TTL Data Book or its equivalent and the 
catalog or data sheets from the manufacturer 
of the microprocessor used. Adam Osborne's 
series of microprocessor books are particu- 
larly good and will also make excellent 
background reference sources. 

Be careful with components. Most elec- 
tronic components are small and delicate. 
They can be easily damaged physically and 
most can certainly be destroyed by excessive 
heat. Diodes, polarized capacitors and most 
integrated circuits can be put in backwards 
which would cause improper operation and 
possible electrical damage. Integrated circuit 
pins can also be bent and broken off very 
easily. Be very careful with every component 
as you install or solder it. 

Another important precaution concerns 
the installation of MOS integrated circuits. 
These devices can be destroyed by static 
electricity. A static charge can be transferred 
to a MOS device by your hand or the 
soldering iron. Most MOS devices are sup- 
plied mounted in protective foam to keep 
the pins shorted. Leave the devices in this 
foam until you are ready to install them. 
When you do, be sure you ground yourself 
or remove any static charge before you pick 
up the device. If you use sockets, the MOS 
damage from static charges can be greatly 
reduced. Any charge from the soldering iron 
will be dissipated in mounting the sockets, 
not installing the integrated circuits. 
Further, when installing the integrated cir- 
cuit in the socket, you can short all the leads 
together by pressing the board and socket 
against conductive foam. 

All of the above recommendations and 
precautions are obvious for the most part. 
It's easy to read them and agree with them, 



Provide yourself with a library of reference informa- 
tion about computers, integrated circuit logic data, 
etc. It will prove to be one of the most valuable 
pieces of "equipment" in your personal computing 
endeavors. 



but if you are to assemble your kit success- 
fully, you absolutely must follow them. It's 
a small price to pay for protecting your 
investment. 

What to Do If You Have Trouble 

Whenever you purchase a kit you should 
prepare yourself for the fact that you may 
make a wiring mistake or encounter a 
defective component. If you plan for this in 
the beginning you will not be surprised if it 
happens. In most cases you will find that it 
is not a serious problem. Instead it is simply 
an inconvenience to overcome. If you ap- 
proach it with the right attitude, you will 
not be dissatisfied with your kit. Here are 
some tips on what to do if you experience 
difficulty. 

When you finish building the kit, follow 
the test, checkout and troubleshooting 
instructions given by the manufacturer. The 
quality of this information varies from one 
manufacturer to another. Some supply no 
information while others furnish detailed 
troubleshooting charts. Use whatever infor- 
mation is available to you first before going 
on with the recommendations given below. 

Question the problem. The first thing to 
ask yourself: Is the trouble you experienced 
really a problem? It may indeed be, but it 
may also be that you are using the equip- 
ment improperly. The controls may have 
been set incorrectly or you may be wrongly 
interpreting the results. The solution to this 
is to read the instruction manual carefully to 
be sure that you are doing things properly. 
In computers, as in flying, cockpit problems 
or pilot errors are a typical source of 
trouble. The hardware may be good, but the 
operator may be defective. Even in simple 
kits this is a very common problem. Due to 
the complexity of computers, no kit will be 
totally immune from this problem. 

Check your assembly. Once you have 
eliminated operator error as the trouble, you 
can assume that you have a hardware 
problem. The first suspect is assembly errors. 
Go back and double check your assembly. 
This is time consuming but it can often turn 
up the problem. A good way to do it is to 
have a friend help you. Often by working 
with someone else you can find the problem 



59 






Be sure to remember the 
motto of a certain very 
large computer company: 
THINK. The application 
of computers as general 
purpose problem solvers 
requires thought on the 
part of the user, whether 
the computer is a kit or a 
traditional high priced 
product. The only com- 
puters which have any 
hope of being totally 
"idiot proof" are those 
which have had the 
thought requirements dis- 
tilled into a well designed 
application program in 
products such as a hand 
calculator, a microwave 
oven controller, a "turn 
key" application system or 
any situation where the 
programming is supplied in 
a packaged solution to a 
problem. 



that you may have overlooked yourself. A 
common mistake is poor solder connections. 
It may be difficult to spot one bad solder 
connection among thousands, and even a 
bad solder joint sometimes looks good. As a 
result, the first step should be to resolder 
each and every connection in the kit. Again 
this is tedious but will often solve the 
problem. To do this, simply touch the 
soldering iron to each solder connection 
briefly to remelt the solder. If you see a wisp 
of smoke come out of the connection, it 
may indicate that the rosin in the joint was 
not sufficiently melted thereby causing a 
poor connection. The joint may have been a 
cold solder joint where no electrical con- 
tinuity existed at all. Simply reheating the 
connection made it good. 

As you arc resoldcring the connections, 
look for solder bridges. This is a thin trace of 
solder that is accidently drawn between 
adjacent pads on the circuit board. The 
solder bridge causes a short. These bridges 
are usually eliminated as each solder connec- 
tion is reheated. But they may not be. As 
you are resoldcring each connection, look 
carefully at adjacent pins to be sure that 
shorts do not exist. Some solder bridges are 
so fine that they arc difficult to find. Use a 
magnifying glass and strong light to help. As 
you go through a complete circuit board you 
may discover connections that you forgot to 
solder or components that did not get 
installed properly. Simply rcsoldering all the 
connections is an excellent way to recheck 
your assembly since it methodically covers 
all points. 

Once you have double checked your 
soldering and assembly, again test the equip- 
ment. Many times the problem will be solved 
and proper operation will result. If the 
difficulty slill exists, the problem may be a 
defective component. Unless you have had 
specific experience in troubleshooting elec- 
tronic and digital equipment, locating a 
defective component can be difficult. For 
that reason, it is best to call for help. 

Seek help. The first step is to ask a friend 
or the manufacturer for help. You may be 
able to find a friend who has built a similar 
piece of equipment or who has experience in 
troubleshooting. Don't hesitate to call or 
write the manufacturer for help. It is the 
manufacturer's responsibility to help you get 
the kit working properly. 

Another alternative is to seek help from 
your local computer store. Most store 
owners will be familiar with common prob- 
lems and may have just the advice, infor- 
mation or help you need. 

Before you ask for help, however, it is 
best to isolate the problem yourself if you 



can. Write down all of the symptoms. Make 
some tests yourself to try to determine what 
is happening or not happening. If the proc- 
essor runs at all, run some simple diagnostic 
programs to attempt to isolate the problem. 
Try to obtain as much information as 
possible before you ask for help. The more 
information that you supply the better the 
quality of the help that you will receive. For 
example, one of the things that you can do 
is measure the power supply voltages. Often 
the equipment is not working simply be- 
cause it is not receiving power. Use a 
voltmeter to check power supply voltage at 
each of the printed circuit boards in the 
equipment. If an oscilloscope is available, 
check for the presence of clock pulses. 

Once you have accumulated as much 
information as possible, write a letter or 
make a phone call to the manufacturer. 
Continue this process until the trouble is 
located. If all else fails, return the kit to the 
manufacturer or your local computer store 
for repair. Above all, don't give up. The real 
fun begins when you get your computer 
running. 

Kit Versus Wired Products: Your Decision 

Kit building is fun, challenging and 
satisfying. It is educational, and you can save 
a lot of money. Most people who have built 
kits successfully highly recommend it. Yet 
some computer hobbyists simply do not 
want to spend the time or become involved 
with kit building. They want to concentrate 
on programming and applications. It is 
probably best that these individuals buy 
wired and tested units. Although this re- 
duces the number of products available, it 
does eliminate the potential problems associ- 
ated with kit building. It also eliminates the 
benefits. 

Before you decide to buy a wired 
product, you should also consider having a 
friend or other individual build the kit for 
you. Often you can locate someone who is 
willing to build a kit for a price far lower 
than you would pay for an assembled unit 
from the manufacturer. I have heard of 
several examples where individuals have 
assembled kits for others simply to be able 
to have the experience of building and using 
the kit themselves for a period of time. 
There arc a number of small companies who 
are in business to build kits for individuals. 
The prices are usually, less than the assem- 
bled and tested units available from the 
manufacturer. 

Even though you may have shied away 
from building a kit, try it. You may find 
that it is easier and more fun than you 
suspected." 



60 










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1276 






Articles Policy 

BYTE is continually seek- 
ing quality manuscripts writ- 
ten by individuals who are 
applying personal systems, or 
who have knowledge which 
will prove useful to our 
readers. Manuscripts should 
have double spaced type- 
written texts with wide mar- 
gins- Numbering sequences 
should be maintained sepa- 
rately for figures, tables, 
photos and listings. Figures 
and tables should be provided 
on separate sheets of paper. 
Photos of technical subjects 
should be taken with uniform 
lighting, sharp focus and 
should be supplied in the form 
of clear glossy black and white 
or color prints (if you do not 
have access to quality photog- 
raphy, items to be photo- 
graphed can be shipped to us 
in many cases). Computer 
listings should be supplied 
using the darkest ribbons pos- 
sible on new (not recycled) 
blank white computer forms 
or bond paper. Where possible, 
we would like authors to sup- 
ply a short statement about 
their background and experi- 
ence. 

Articles which are accepted 
are typically acknowledged 
with a binder check 4 to 8 
weeks after receipt. Honorar- 
iums for articles are based 
upon the technical quality and 
suitability for BYTE's reader- 
ship and are typically $25 to 
$50 per typeset magazine 
page. We recommend that 
authors record their name and 
address information redun- 
dantly on materials submitted, 
and that a return envelope 
with postage be supplied in 
the event the article is not 
accepted." 



Continued from page 14 

perhaps the extreme case for shipment of 
BYTE magazines to foreign subscribers. Not 
satisfied with waiting three months or so for 
the very current information we put out in 
BYTE each month, he started immediately 
to search for alternatives. 

His first urge was to import BYTEs in 
sufficient quantity to sell to his neighbors in 
the Sydney area, thereby assuring (so the 
theory went) that he got them on a timely 
basis by way of a bulk shipment. With that 
in mind, he figured that he'd send them air 
freight to his shop, then distribute them. Nice 
theory, but, in bulk it cost US $1.50 or 
more to ship each magazine by air — so his 
bulk shipments ended up going on the same 
boats which carry the surface mail. (It costs 
nearly US $6 to send just one copy by air 
mail!) So much for that theory. After taking 
a bulk shipment of BYTE each month for 
several months, John hit upon another solu- 
tion to the problem: Maybe he could talk 
BYTE into printing locally for distribution 
in Australia. Shortly after that brainstorm 
struck, we got our first long distance phone 
call from John Bannister. 

Phone calls from Australia arc most inter- 
esting. You'd expect that a certain decay in 
quality would occur as the distance in- 
creases. But much to our surprise, the phone 
conversations with John, whether by cable, 
radio or satellite, often came through with a 
quality perhaps half an order of magnitude 
better than a simple transcontinental con- 
versation with an advertiser in California! Of 



course, for such calls, either one party or the 
other is bound to be half asleep, for the time 
differential is 11 hours between EST and the 
time zone which encompasses Sydney. At 
any rate, the first phone call was to explore 
the possibility of setting up a new Australian 
publishing house with John as the principal, 
whose purpose would be to print an Aus- 
tralian English language version of BYTE. 
Thus began a scries of long distance nego- 
tiations, proposals, Telex messages and 
phone calls concerning the arrangements. 
Now that all the negotiating and arrange- 
ments have been crystalized into a signed 
contract, we can announce what has 
transpired. 

Beginning with the January 1977 issue of 
BYTE magazine, two new editions will be 
published for readers in the more techno- 
logically sophisticated areas of Southeast 
Asia. One edition, in English, will be printed 
and distributed to subscribers in Australia, 
New Zealand, Singapore, Hong Kong, the 
Philippines and other countries where 
readers of English are interested. -A second 
Asian edition will be translated into 
Japanese and distributed in Japan. The 
editorial content of both new editions will 
be identical (English edition) or identical 
scmantically if different in detail (Japanese 
edition). For the first issues, the advertising ^ 
copy will also be identical; but John's office 
in Sydney and his agent in Tokyo will solicit 
local advertising for these editions, while 
preserving the option for our US advertisers 
to reach these foreign markets. 

Technologically, the arrangement is fairly 




A BYTE family portrait, 
circa December 1 9 76. 
Clockwise from top left 
are Manfred Peschke, Vir- 
ginia Peschke, John Ban- 
nister and Carl Helmets. 
("Note: the reader probably 
suspects that all those im- 
pressive looking books in 
the background are the 
world's greatest collection 
of computer tomes. While 
they do indeed look im- 
pressive, they 'd really only 
impress a farmer since 
they contain the genea- 
logical records and trivia 
of the Guernsey cow - 
breed.) 



62 



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Processor Technology s Subsystem "B" 
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You get both RAM and PROM memory, 
parallel, serial, cassette and video display inter- 
faces, and software. Software includes a 512 
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any Processor Technology CUTS CByte/Kansas 
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subroutines in ROM, similar to those in a Sol 
personality module, are used by many Processor 
Technology software packages to improve 
program efficiency. You'll find you rarely need to 
touch your front panel switches. With our 
Subsystem "ET you are up and running as soon 
as you turn on the power. 

Three subsystems are available, depending 
on your memory requirements. Each Subsystem 
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as listed below. Each is dependent upon our new 
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Memory) which provides 1024 bytes of low power 
static RAM and 512 bytes of preprogrammed 
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I want Subsystem n B" to get my Altair or 
IMSAI up and running. 



□ Enclosed is a check for S_ 



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No shipping charge. 

□ Mastercharge # 

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Name 



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John Bannister (left) and 
Carl Helmets discussing 
the problems of translating 
BYTE into Japanese, while 
perusing the Japanese edi- 
tion of Scientific Ameri- 
can, December 1976. It 
turns out that translators 
do some interesting things. 
For example, in the trans- 
lated version of an article 
by an author with a name 
of, for example, "Lane, " 
the initials stay in Roman 
characters, but the sur- 
name — since it has a 
generic equivalent in 
Japanese script — is trans- 
lated. But if the surname 
has no immediately identi- 
fiable generic root or 
equivalent, it remains in 
English spelling as do tech- 
nical terms with no direct 
equivalent. 




simple. At the time we give the final OK to 
the negatives from which BYTE is printed 
each month, our printer, The George Banta 
Company of Menasha Wl, will make dupli- 
cate copies of all the negatives, and send 
them to Sydney where John will modify the 
book to fit the local edition. Eventually this 
will include local advertising, local club and 
newsletter information, and possibly putting 
in new product in formation and related 
items of interest to local readers. The bulk 
of the material in the magazine will, how- 
ever, remain identical to the US edition. 

All our Australian, Japanese and Asian 
subscribers will be given the option of 
converting their subscriptions to the local 
edition which, due to its simultaneous pub- 
lication, will be up to date as opposed to 
three months behind clue to shipping delay. 

Once it became apparent that we would 
be able to get together on this venture, John 
made the trip from Sydney to Peterborough 
NH via Lost Angeles. I call it Lost Angeles 
because the airline on which he was traveling 
managed to lose his luggage in the transfer. 
Arriving at Logan Airport, Boston (after 
neglecting to tell anybody what flight he was 
coming on), he was met by Debra "Sher- 
lock" Boudricau of BYTE, who in a feat of 
deductive reasoning and investigation, 
managed to pinpoint the flight and John 
Bannister, using only his one statement, "I'll 
be there at 8:30 tomorrow morning." As 
recounted later, it was a simple deduction: 
There was only one transcontinental flight 



out of Los Angeles which arrived at Logan at 
8:30 AM, and an Australian newly arrived is 
easy to spot: After an elapsed travel time of 
22 hours with essentially no sleep, watch for 
the only person who is walking in a daze. 

After initial greetings on arrival in Peter- 
borough, John sacked out for about 15 
hours, after which we began an intensive 
scries of conferences on the details of 
publishing remotely, how to arrange ship- 
ment of the negatives, timing the monthly 
operation, etc. After a busy two days, I 
picked up John at midnight on December 1, 
and we spent the wee hours at my home and 
laboratory discussing things and comparing 
notes on the problems of computer enthu- 
siasts in our respective countries. After I 
dropped him off back at the motel around 4 
AM, we all showed up at the BYTE offices 
and took the pictures accompanying this 
editorial. Then, with the contract signed, 
Virginia and Manfred Peschke and John 
went to New York (by way of Boston) for a 
visit to Scientific American (see box) and 
some of the fabled surplus outlets which are 
reputed to still exist in that city. Manfred 
and Virginia finally saw John off to Aus- 
tralia from New York and returned to 
Peterborough that weekend. 

One of the details of the Australian 
arrangement is a surprise and delight to g 
Deborah Luhrs, who has been with BYTE 
nearly from the beginning. In order to assure 
a bit of experience, as far as handling 
subscriber orders and managing an office is 



64 



IF YOU'RE STILL PLAYING GAMES 
ITS BECAUSE YOU HAVEN'T SEEN 
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ANoteofThanksto Scientific American 

We at BYTE wish to thank David Trussell 
of Scientific American for taking time out of 
a busy schedule to meet with Virginia and 
Manfred Peschke and John Bannister of 
BYTE to discuss some of the problems and 
pitfalls of publishing foreign language edi- 
tions of magazines. With the Japanese lan- 
guage edition of BYTE we begin our first 
such version in translation, and it proved 
quite helpful to us to have a bit of informal 
and friendly advice from people experienced 
in that endeavor. 

We also learned that Scientific American, 
which is printed on extremely high quality 
paper, has lately been having trouble procur- 
ing supplies. The paper is necessary to 
achieve good reproduction of the color 
images which are so characteristic of their 
product. Who could possibly be eating up all 
the good quality paper? It turns out that 
there is a hot competition between Scientific 
American, Oui and Penthouse to see who 
can buy all the special paper. This quality 
magazine is being skinned alive! 



concerned, John thought it a good idea to 
take up a suggestion which Virginia made: 
that Debbie should travel to Australia for a 
few months to help set up the office of th? 
new firm, BYTE Publications | Austr/Japan] 
Pty Ltd. Although Debbie left today 
(December 6 1976) as this editorial is being 
written, she still doesn't quite believe that 
it's all really happening! 

Who is John Bannister, our new "Affiliate 
Publisher — Southeast Asian Editions"? 
John is a man of considerable experience in 
the Australian electronics industry, in the 
Sydney area. He became interested in small 
scale data processing systems following Don 
Lancaster's original TV typewriter articles in 
Radio Electronics and the later articles by 
Jonathan Titus and company on the Mark-8 
processor in that same publication. His 
assistant in business operations (book- 
keeping and moral support department) is 
his wife Pamela, and he's well aware of the 
possibilities for using personal computers in 
the education of his two preschool age 
children. He's convinced (as are we) that it is 
just a matter of time until the revolution of 
personal computing we've seen in this 
country finally reaches his own country and 
Japan — to say nothing of the other tech- 
nologically oriented countries of the world." 



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66 



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San Francisco Bay Area — Where It All Started - Has Its First Home Computing Convention 

7,000 to 10,000 People 

100 Conference Presentations 

200 Commercial & Homebrew Exhibits 

Two Banquets with Outstanding Speakers 

Special-Interest Social Centers 

Publication of Proceedings Being Planned 

In Northern California's Largest Convention Facility, San Francisco's Civic Auditorium 

CONFERENCE SECTIONS ON HOME COMPUTING 

Being Planned 



Computer Graphics on Home Computers 
Computer-Driven & Computer-Assisted Music Systems 
Speech Synthesis Using Home Computers 
Computers & Amateur Radio 
Computer Games: Alphanumeric & Graphic 

• Personal Computers for the Physically Handicapped 
Computers & Systems for Small Businesses 

• Tutorials for Hardware Novices & Software Novices 



■ Software Design for Personal Computers 
• Microprogrammable Microprocessors for Hobbyists 
> Optical Scanning for Inexpensive Program & Data Input 
» Floppy Disc Systems for Home Computers 
» Hardware & Software Standards for Personal Systems 
» Seminars for Club Leaders, Editors, Organizers, etc. 
» Personal Computers in Education (associated with a 
University of California short-course) 



AND MUCH MORE 



PRESENT-WORLD & FUTURE-WORLD BANQUET SPEAKERS 



Banquets to be Held in 
Fascinating Speakers will 

• Frederik Pohl, Science Fiction Writer; 

Lecturer to NASA, American Astronautical 
Society, New York Academy of Sciences, 
World Future Society, etc. 
Robots You Can Make for Fun & Profit 

• John Whitney, Pioneer Computer Film Maker, 

Computer graphics experimenter under grants 
from NEA, Guggenheim Foundation, & IBM 

Digital Pyrotechnics: The Computer in Visual Arts 



San Francisco's St. Francis Hotel 
Discuss the Past, Present, & Future 

• Henry Tropp, Mathematician, and Principal 

Investigator for History of Computers 
Project jointly sponsored by the 
Smithsonian Institution & AFIPS 
The 1940's: The FIRST Personal Computing Era 

• Ted Nelson, Author & Fantast, Director of the 

Xanadu Electronic Literary Network, 
Lecturer at Swarthmore College 

Those Unforgettable Next Two Years 



aprll XE5-X7, 1977 



lan francisco 



©77-1 -12a by Computer Faire 



68 





















^MICROCOMPUTERStyK X 3 kt 

* 7A f ^ r r -J J.M T l T ' "'•"' -'- rT 





kCuf out, or photocopy ; then fold, and tape in position. 






*»M 



^*. 



FIND OL/T ALL THE DETAILS 



GET YOUR FREE COPY 

OF THE 

SILICON GULCH GAZETTE 

• Details of the programs & speakers 

• Information about the banquets' arrangements 

• Accommodations information, & registration forms 

for the St Francis Hotel (Faire Headquarters Hotel), 
& the other three Computer Faire hotels 

• Pre-registration details for the Faire 

(reduced admission for those who pre-register) 

• Details of the Proceedings expected to be published 

• Articles about the homebrew exhibits 

• Weather information, & tourist trivia regarding 

San Francisco 

• Listings of the commercial exhibitors 

• AND, just to make it interesting: 

— "Hot news", & raging rumors from "Silicon Valley" 

(the San Francisco Bay Area) 

— Product announcements, equipment descriptions, 

hardware & software news, etc. 

CO-SPONSORS INCLUDE AMATEUR, 

PROFESSIONAL, & EDUCATIONAL GROUPS 

• The two largest amateur computer groups: 

Homebrew Computer Club 

Southern California Computer Society (SCCS) 

• Both Bay Area Chapters of the Association for 
Computing Machinery (ACM) 

San Francisco Peninsula Chapter 
Golden Gate Chapter 

• IEEE Computer Society's Santa Clara Valley Chapter 

• California Mathematics Council 

• Stanford University's Electrical Engineering Dept. 

• University of California's Lawrence Hall of Science 

• People's Computer Company (PCC) 

• Community Computer Center 

• Bay Area Microcomputer Users Group (BAMUG) 

• Professional & Technical Consultants Assn (PATCA) 

• Amateur Research Center 



Vapril 15-17, 1977 - 



san franciBco i 



©77-1-12 by Computer Faire 



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69 









Simplified Omega _ 



Ralph W Burhans 

Research Engineer and Lecturer 

Ohio University 

Electrical Engineering Dept 

Athens OH 45701 




Photo 1 : Mini-0 microcomputer interface, with the radio frequency front 
end. The RF front end (in the foreground) is essentially a receiver for 10 kHz 
radio signals broadcast by Omega transmitters widely spaced around our 
planet. The device was built in prototype form using perforated board and 
sockets, as seen here. The microcomputer interface (to a JOLT system) is via 
the mounted plug at the right of the interface box (rear unit in photograph). 



Antennas 

The receiver is designed to use an E-field 
short whip or wire antenna of random 
length. This type of antenna is often called 
an "E-field" antenna because it responds to 
the electric field component of the radio 
signal. A 20 cm wire will do in many cases if 
the antenna is mounted in the clear. A 10 
meter length wire works well in cases where 
there is not a lot of local 60 Hz harmonic 
interference. Unfortunately, the Omega 
System's 10.2 kHz is exactly the 170th 
harmonic of 60 Hz and urban laboratory 
monitors sometimes have problems with 
bursts of 60 Hz interference from high 
power SCR-TRIAC controls or rotating elec- 
trical machinery. The boat owner or aviation 
buff usually doesn't have problems with AC 
line interference and a short whip mounted 
vertically will often suffice for the antenna. 

Preamplifier 

The preamplifier of figure 1 is con- 
structed in a small weatherproof box with a 
tight feedth rough insulator or fitting right at 
the antenna and a coaxial cable lead-in for 
the signal back to the receiver (see photo 1). 
The coax supplies both power to the preamp 
and a preamplified Omega signal back to the 
front end module. The circuit is not critical 
but should be adjusted for a broadband peak 
at about 10.2 kHz by minor changes in the 
0.02 juF capacitor across the inductor. 
Tapping down on the 600 ohm line output 
transformer improves the Q of this simple 
bandpass filter circuit. 



w 



J ^ 

WHIP 

ANTENNA 

INPUT 



® 



2N5I39 






icyF 



TO FRONT END 
(FIG 2) 



<LJ 



iJlj 1 9 



VYYYYV^ 



»-)r-» 




m 



Figure I: Mini-0 antenna preamplifier, 10.2 
kHz. This preamplifier is shown as con- 
structed in one version in photo 4. The 
2N5I39 transistor must be selected for a 
high p. Power for this preamp is sent up the 
coaxial cable from the front end unit, thus 
sharing the same wire with the signal. The 
transformer, 7] is a 600 ohm center tapped 
to 600 ohm center tapped line to line 
transformer, a Mouser 80TM016 or 
80TM009 part number in electronics cata- 
logs. The Q factor for this amplifier is 2, 
with a gain of 20 dB at 10.2 kHz. 



70 









Receiver Details 



ping down on the 600 ohm line output 
transformer improves the Q of this simple 
bandpass filter circuit. 

The preamplifier has an input impedance 
of 1 megohm with a 1 k ohm series resistor 
as a current limiter for gross interference 
such as from nearby lightning discharges. We 
have yet to burn out a 2N3819 JFET in 
these front ends but have had trouble with 
similar MOSFET input transistors in earlier 
preamplifier systems. Other J FETs like the 
MPF102 will work just as well. 

The 2N5139 PNP transistor provides a 
gain of 20 dB or so in this circuit and the 
transistor should be selected for a high beta, 
greater than 100 if possible. The Q of this 
circuit is about 2 which supplies some 
desirable reduction of low frequency and 
h high frequency interference in the very first 
stages of the receiver. 

Front End 

The heart of the radio frequency analog 
circuitry involves a multistage bandpass filter 
with two active filters and two passive 
mechanical filters, as in figure 2. The signal 
from the preamplifier drives the first Seiko 
SM-31 R mechanical filter directly from the 



Omega Navigation is a method of determining where your boat or plane is 
currently located, anywhere on the globe. It is a "free" method of navigation 
to a certain extent, since it is sent out by the cooperating nations via radio 
transmissions for shipping and defense traffic, but is available to any 
technological hitchhiker willing and able to build the proper interface. (Free 
in this instance is defined to mean the accounting for each person's share of 
the tax cost is so diffuse it can 't be traced.) 

In this month's installment, Ralph W Burhans continues the Omega 
information with the description of the detailed function and circuitry of an 
Omega navigation receiver which can play with any microprocessor system 
possessing an 8 bit input port. [The Mini-0 Omega receiver design is intended 
for an experienced amateur electronics person, and to the best, of our 
knowledge is not yet available in kit form for the novice.] Howdoyou use it 
once it's built? The details of the software will have to wait until the third 
and final part of this series, by Richard J Salter, which will appear in the next 
BYTE. 



680 ohm isolating resistor which supplies 
power to the preamplifier. This first stage of 
mechanical passive filtering is followed by an 
active tunable bandpass filter to help reduce 
sideband responses and increase the system 
gain. A 1 k ohm pot at the output of this 
first active filter is used as a radio frequency 
gain control. The next stage is quite similar. 



LM324 QUAD OP AMPS 

f 500 



N9I4 DIODE 
BRIDGE LIMITER 



FROM 

PREAMPLIFIER (O- 
(FIG I) 




Figure 2: Mini-0 mechanical filter front end amplifiers. This active circuit uses two mechanical filters manufactured by Seiko to 
provide a narrow bandwidth of 14 Hz at the -3 dB points and a gain of 40 to 60 dB. The output passes through a diode bridge 
limiter implemented with an operational amplifier section, prior to reaching the zero crossing detector of figure 3. The physical 
construction of this circuit is shown in photo 3. 



71 




Photo 2: Mini-0 in operation on the bench. The setup shown here uses a Teletype Model 33 ASR with the JOLT computer (at 
right in front of power supply), and the Sinclair clock reference (in front of interface box on bench). The display on the 
oscilloscope shows output from a lines of position digital to analog conversion output described (in concept) in part I of this 
article. 



The Seiko filters are available 
from: 

Seiko Instruments Inc 
2990 W Lomita Blvd 
Torrance CA 90505 
Phone (213) 530-3400 

Seiko also has filters for the 
11.333 and 13.600 kHz 
Omega channels; write for 
information. The original 
SM-B filter has now been 
changed to type SM-31 R. 

Order a SM-31 R 10.200 kHz 
2 piece kit: unit cost $8.50 X 
2 pes = S17, postage and 
handling charge ■ S1.50 
[6% sales tax for California 
Residents only] . 



We have found that it is usually necessary to 
provide the 1 k load resistors to ground at 
the output of each of the operational ampli- 
fier stages as shown, to help reduce regene- 
ration problems [ie: oscillations neither 
planned or desired | which depend on the 
particular parts layout on the circuit board. 

The overall system gain and frequency 
response can be altered by changing the 
6.8 k ohm feedback resistors across the first 
two op amps to 15 k ohms or so. However, 
too much gain here results in instability. The 
overall gain of this filter and limiter circuit is 
about 40 dB as shown. The bandwidth is 
about 14 Hz at the —3 dB points and the 
skirt selectivity is excellent, about — 80 dB 
down at the next Omega channel frequency 
of 11.33 kHz! 

Several other types of front end bandpass 
filter arrangements have been used with 
Vernitron ceramic filters and with Statek 
quartz tuning fork filters. However, these are 
more difficult to fabricate and adjust prop- 
erly or involve more expensive circuitry 
compared to that required for the Seiko 
SM-31 R mechanical filters. 

Alignment of the filter of figure 2 is quite 
simple. A stable function generator with a 
sine wave output at 10.200 kHz is fed to the 
input terminal through an isolating capacitor 



and attenuator. The output from the limiter 
stage is observed on an oscilloscope and 
tuned for a peak amplitude by adjusting 
both 500 ohm trimmer resistors on the 
bandpass stages. It might be desirable to 
check the impedance matching by altering 
the 0.002 jitF input capacitors from each 
SM-31 R filter. These serve to "tune" the filter 
peak to about 10.200 kHz but are rather 
broad. A capacitance between 0.002 and 
0.003 mF is usually required and a fixed 
ceramic type capacitor is adequate or 
perhaps two parallel ceramic capacitors to 
adjust each filter peak to 10.200 kHz (such 
as 0.002 in parallel with 0.0005). In tuning 
the filter circuit be sure to attenuate the 
signal generator to a low level so that the 
limiter is not clipping the peaks at the 
output. The operation of the limiter can be 
checked by increasing the drive to the filter 
to the point where the output starts to look 
like a square wave with rounded-off corners. 
The limiter peak-to-peak threshold is about 
1 V using 1N914 diodes. Other types of 
limiter circuits using the MCI 357 or 
LM2111 IC chips have also been used but - 
the simple diode bridge circuit of figure 2 is 
adequate for most Omega users. If you 
happen to have a dual channel oscilloscope, 
the phase shift versus signal amplitude may 



72 




Photo 3: Mechanical filter front end board. This picture details the construction of the mechanical filter front end for the 
Mini-0 receiver, described by the circuit diagram of figure 2. The potentiometer hanging loose at the left is the 1 k RF gain 
potentiometer, Rl in figure 2. The board shown here also includes the zero crossing detector of figure 3, at the right. 



be checked by observing the input signal on 
one channel and using this to synchronize 
the scope sweep while observing the filter 
output on the other channel. There should 
be very little shift of the phase as the signal 
level is increased up to the point of limiting. 
At the limiter threshold only a slight phase 
shift should be observed. If a large change in 
the phase when limiting is observed, it 
usually means the circuit layout is poor and 
some kind of regeneration is taking place, or 
undesirable feedback; extra bypassing of the 
V/2 power bus with a tantalum low in- 
ductance capacitor of 10 /iF might help, or 
reduce the overall circuit gain by changing 
the active filter feedback resistors to a lower 
value. 

Zero Crossing Comparator 
and Envelope Gate Generator 

The output of the limiter of figure 2 
drives the comparator circuit of figure 3. 
The 10.2 kHz zero crossings are obtained 
from one section of a quad LM339 com- 
parator integrated circuit. This circuit is 
designed with a small amount of hysteresis 
and is intended to be centered on the V/2 
output level of the limiter stage output DC 
level. LM339s are not perfect and usually 
have a slight offset so that it is desirable to 
trim the exact operating point by summing a 



very small correction from a resistor re- 
turned to the positive power supply of +5 V. 
A value of 500 k ohms to 2 megohms is 
usually sufficient with 750 k shown in the 



Rz ^jL^L ADJUST FIXED R 



^>(3) + 5V 



(V/2 BUS 



INPUTS FROM 

FRONT-END 

CFIG2) 



750K 




FOR BEST THRES- 
HOLD OF COMPAR- 
ATOR 



- 1 — mn„F POWER PIN BY- 
T N ' ^ PASSING ON LM339 
k o (|2)GND 



OUTPUT 

lzx> |02ZX 
■s^ (ZERO CROSSINGS PER SECOND) 
(TO FIG 7) 



QUAD LM339 COMPARATOR 
+ 5V 



AUTO START 
-fAS>GATE OUTPUT 
(TO FIG 4) 




Figure 3: Zero crossing detector. This circuit shows the LM339 comparator 
sections used to determine zero crossing transitions (A), monitor the current 
signal level (B) and generate the automatic starting gate output (C) based on 
current signal level. The zero crossings output threshold is set by resistor R2, 
which must be selected to give the best threshold response. The auto start 
output is an ''envelope gate ": It is high when the signal is above the threshold 
set by R3, and low when below that threshold. 



73 









f5V 



AUTO- START 
GATE FROM 
FRONT-END 



MANUAL ;; 
CLEAR f] 



3-POSITION 
SLIDE SWITCH 




>P F ^ 



£ 



L> 

ON 

w 

Hz 

rST 

It 



20M 



2'5Hz 
CRYSTAL 



L> 



> 330K 
^ 24 P F 



<3 



ALTERNATE: SINCLAIR 
RADIONICS 

"BLACKWATCH" 2 5 Hz 
SOURCE (SEE FIG 6) 



2 ID (Hz) 



-HO 



R Ql 04 012 



C 4017 CA 

R 2 7 



(0.8Hz) 
J 



ROI 234567 



2 iH Hz 2 M Hz, 



TIMING TO 
INTERFACE 
FIG 7 



l25mS STROBES 
FOR MEASUREMENT 
WINDOW FLIP FLOP (FIG7) 



LED STATION INDICATORS 



) .1Hz CYCLE 

(10 SEC) 



DM8865 LED 
DRIVER 



Figure 4: Housekeeping timer circuit (HKT). The housekeeping timer is used 
to generate all the signals needed by the interface. A crystal oscillator is 
shown with a 2? 5 Hz (32.768 kHz) frequency, with wiring indicated for use 
of the Sinclair Radionics <( Blackwatch ,t wristwatch as an alternative source of 
the signal. (If the watch is used, omit the crystal oscillator.) A three position 
slide switch is used to control operation modes, which include automatic 
start, manual starting or a clear operation. The LED display driver outputs of 
the DM8865 provide a continuous monitor of the Omega cycle, and the A 
slot is monitored by the interface to the computer to give software a timing 
reference to stations. 



diagram of figure 3. The idea here is to 
adjust the comparator such that it will 
provide a square wave output with as low as 
1 mV peak-to-peak input centered on about 
V/2. This threshold will correspond to about 
10juV peak-to-peak at the antenna terminal 
(about 3 /.iV rms) which is usually well 
below the antenna noise level when the gain 
ahead of the comparator is about 60 dB. The 
front end gain will be about 20 dB for the 
preamplifier plus a minimum of 40 dB for 
the filter and limlter which provides 60 dB 
total. More gain can be provided if required 
by changing the amplifier feedback resistors 
on the active filters as mentioned previously. 
Thus the zero crossing comparator should 
provide an output square wave for essen- 
tially all signals and noise when the antenna 
is connected to the preamplifier. The output 
of the comparator is a hard limited square 
wave, but the filter-limiter circuit has what is 
known in the trade as a clipped linear 
characteristic. The edge position of the 
comparator square wave contains the basic 
phase information of the Omega signal plus 
the noise developed at the antenna within 
the filter bandwidth used. 

The other sections of the comparator are 
used to provide an envelope output signal 



TT 

E F 
I I 

! ! 



TT 



o- 



"A" Tl ME SLOT 
SELECT 
(TO FIG 7) 



1 vw-»- 



+ 5V 



47K 



with a peak detector and an adjustable 
threshold gating circuit. The peak detector 
drives a signal level indicator which is handy 
for observing strong signals like the North 
American D channel on 10.2 kHz, as well as 
the overall receiver noise level. The meter 
should kick upscale slightly when the anten- 
na is connected even in a very electrically 
quiet environment. The typical noise level in 
the 10 kHz region will vary from 1 /LiV to 
100^V per meter of antenna length (assum- 
ing a perfect energy transfer at the antenna) 
for a receiver bandwidth of 15 Hz or 
so. The Omega signals will vary from a low 
of about 10juV to a high of 1000/uV 
depending on the range of the observer to 
the Omega transmitter. The noise level 
during local thundershowers can be much 
greater than the signal, and 60 Hz harmonic 
interference can often completely obliterate 
Omega signals as observed on a scope at- 
tached to the radio frequency front end. 
However, the digital processors which follow 
the zero crossing edge output can track 
signals buried in a large amount of noise 
with proper programming. [Software is the 
touchstone of computer applications.] 

The adjustable threshold gate is used as 
an automatic start signal for operating the 
housekeeping timer (HKT) circuitry. We 
usually also connect an LED from +5 V 
through a 330 ohm series resistor directly to 
this gate output point to indicate when the 
strong D channel is on. An audio beeper 



74 



circuit connected at this point is also a 
handy device when first starting to observe 
Omega signals. This amplitude gate output is 
zero when on, so it operates as a current sink 
when driving external digital interface hard- 
ware. We have found that this circuit will 
start the digital logic operating 95% of the 
time or more, even in the presence of a lot 
of noise because the D channel Omega signal 
is quite strong for most observers in North 
America. For others, a manual start option is 
provided in the housekeeping timer circuit, 
and for the very sophisticated user, an 
automatic synchronization routine can be 
developed using the microprocessor with 
appropriate software. 

Housekeeping Timer and Local 
Clock Oscillator 

In order to operate an Omega receiver it 
is necessary to have some sort of timer 
circuitry and reference clock oscillator. The 
timer provides a means of telling the receiver 
which stations are being received, and the 
clock provides a reference for comparing the 
phase differences among stations. The clock 
oscillator drives the timer circuitry through 
an appropriate series of divider stages. A 
very simple housekeeping timer circuit based 
on a clock frequency of 2^5 Hz is shown in 
k figure 4. 

A 32.768 kHz quartz crystal of the type 
found in digital wristwatches is used. The 
timer circuitry here provides a number of 
very convenient gating and control signals 
for operating external microprocessors or 
hardware digital sensor systems. The timer is 
started with a master reset gate (MR) ob- 
tained from the front end automatic start 
output or from a manual pushbutton. A 
set-reset flip flop holds the timer on as long 
as the receiver is operating. The timer can be 
reset by switching to the stop position (or 
clear) and momentarily operating the same 



control pushbutton. The housekeeping timer 
tells the receiver user where the Omega 
sequence is with LED indicators. For a 
microprocessor interface only one of the 
stations need be selected to identify where 
the Omega sequence is, such as starting at 
the A or D channels. Beginnners might find 
that a string of eight LEDs, one for each 
time slot, is a value in understanding the 
operation of the Omega sequence. 

A uniform measurement window method 
has been used in this housekeeping timer 
circuit. If the clock is started at the be- 
ginning of the D Omega time slot, then the 
sequence of gates is as shown in figure 5. A 
measurement window for each Omega time 
slot is obtained with additional clear, stop, 
and read gates for each one. The measure- 
ment window width can be altered by start- 
ing on pulse 1 and stopping on 8 instead of 
2 and 7 as shown in figure 4. The goal here is 
to provide an easy way of telling the 
microprocessor when the measurement is 
valid. The HKT generates eight time slots 
every 10 seconds with 10 shorter 125 ms 
control gates for each one under the option 
of whatever the user desires to program. 

Clock Adjustments 

The 32.768 kHz clock should be adjusted 
for an offset of 5X 1 _ 6 or less. A reasonably 
good frequency counter with a built-in 
1 MHz temperature compensated crystal 
oscillator time base can be used. First adjust 
the trimming capacitor on the clock oscilla- 
tor to read 32.768 with a 1 second counter 
gate time. Then adjust for 32.7680 with a 1 
second gate time. If a period averaging 
feature is available on the frequency 
counter, 1 04 periods of the 32.768 fre- 
quency will result in a number like 30.51757 
microseconds which gives a reading of ±3 
parts in 10^ precision with respect to the 
frequency counter time base crystal. If you 



Photo 4: The RF preampli- 
fier, shown built with a 
homebrew printed circuit 
board and mounted in a 
shielded metal housing. 
The antenna is mounted at 
the left, with the connec- 
tion to the receiver front 
end box via coaxial cable 
at the right. 







75 






AUTO START 



NO SIGNAL 
GAP, 0.2s 



SLOT 



J — U 

1 1 1 1 1 1 1 I I „ I UNIFORM 1.25s TIME SLO 

°| l | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | WITH TEN , 125 ms GATES 

n 

j \ c\ pap 



JM_ 



-625ms- 



W//////A 



El. Is 



_r 
j" 



Figure 5: Timing diagram, 
showing how the logic of 
figures 4 and 7 combine to 
produce a hardware de- 
fined measurement win- 
dow which will validly 
sample a segment of the 
signal from each station. 
The diagram assumes that 
the automatic start begins 
on the leading edge of the 
signal from the D station. 
The portion of the trans- 
mission interval between 
dotted lines in the E, F t G, 
H } A, B and C station 
signals is monitored by the 
Mini-0 software through 
the interface. 



START (BEGIN WINDOW) 



STOP (END WINDOW) 



MEASUREMENT WINDOW 



READ OR WRITE 



TO 
UN 



TRANSMITTING TIME POSITION 
OF OTHER STATIONS RELATIVE 
AUTOSTART ON D WITH 
IFORM MEASUREMENT 
WINDOW 



1_ 



do not have a frequency counter, the nearest 
CB repair shop usually does, and the clock 
may be carried to the frequency counter 
location for initial adjustment. Once 
adjusted the clock may be operated in the 
on-off mode with occasional checks using 
the Omega signal to estimate the offset for 
periodic recalibration. 

Commercial and military Omega receivers 
often use a temperature compensated crystal 
oscillator clock on a frequency like 
2.611200 MHz (28 X 10.200 kHz). Suitable 
divider chains can be easily assembled to 
generate all of the Omega time slot functions 
from this particular frequency. It is also 
possible to devise frequency synthesizer cir- 
cuits based on 5 MHz standards and some 
receivers have an atomic clock reference for 
use in the direct ranging mode. The 2^5 Hz 
watch crystal oscillator provides adequate 
stability when treated with some care and is 
many orders of magnitude less expensive 
than other methods. 

Other 2^5 Hz Clocks 

A Sinclair Blackwatch or the Westclock 
GT-500 wall clock movement have been 
used to provide the 2"! 5 Hz signal with an 



isolating high impedance buffer amplifier. A 
circuit to modify the Sinclair watch kit is 
shown in figure 6. The output of this circuit 
is used to drive the oscillator of figure 4 by 
removing the crystal from the circuit of 
figure 4 and driving between ground and the 
input side of the oscillator gate right across 
the frequency trim capacitor. The GT-500 
clock requires an additional 4024 divider 
stage to generate 2 "1 5 Hz from the crystal 
frequency of 2^1 Hz. 

Marine navigator types might find that a 
clock such as the Sinclair Blackwatch which 
has a digital display for time of day in 
hours-minutes, or minutes-seconds, is of 
value also as a celestial navigation chro- 
nometer. Once the clock has been properly 
adjusted, the user can even estimate when 
the D channel should be operating by 
keeping track of the clock offset on a daily 
basis using the seconds readout. The Sinclair 
watch kit can provide better than 1 second 
per week offset with respect to Omega. Thus 
the receiver user can also start the receiver 
manually by operating the pushbutton when 
the estimated D channel second interval is 
displayed on the clock readout. The gating 
system of figure 5 with uniform time slots is 
designed such thaferrors up to a quarter of a 
second can be tolerated and still provide 
some measurement window. The automatic . 
starting gate will start using the strong D 
channel within 50 ms of the correct station 
spacing illustrated in figure 5, and manual 
push to start operation can be achieved 
within 100 ms with some practice in "clock 
watching." 

Microprocessor Interface 

The next step in the receiver operation 
involves converting the 10.2 kHz Omega 
zero crossings to a sampled set of 6 bit 
numbers. First a single chip rate multiplier, 
an RCA CD4089BE, multiplies the 
32.768 kHz frequency by 5/16 to generate 
10240zps (zero crossings per second) clock 
rate. There will be some jitter at the LSB 
rate but this will wash out in the processor 
which needs only six of the eight bits for 
Omega use. 

The Omega zero crossings are fed to a 
digital mixer circuit consisting of one D flip 
flop ( ] / 2 4013) and mixed with 2*11 Hz ob- 
tained from the housekeeping timer circuit 
of figure 4. The mixing formula here is: 



I F = f — (m+1)2n 



where: 



IF is the intermediate frequency in Hz, 

f is the input frequency, 

m is the harmonic number of 2n Hz 



76 



which is nearest and lower than the input 

frequency, 

n is an integer. 

The result for Omega is IF = 40 Hz when 
2n = 2048 Hz and m = 4. We have now 
converted the Omega 10.2 kHz signal to a 
40 Hz signal using simple digital mixing 
where the phase of the edges of the 40 Hz 
track the Omega phase within 2048/40 or 
within 51.2 parts per cycle. This is a con- 
venient number in that 5 X 51.2 = 2°. A 
6 bit number (1 part in 64) can specify the 
Omega phase but the precision of measure- 
ment will only be 1 part in 51.2 of the 
actual Omega phase. This is more than 
adequate for simple Omega receivers which 
typically have errors of ±1 nautical mile, and 
8 miles represents an Omega lane. In effect 
the binary system generates phase to within 
2/1 OOths of an Omega cycle or lane as 
applied to distance measurement over the 
earth surface. It is also worth noting here 
that the phase direction of the 40 Hz signal 
changes opposite to that of the Omega 
signal, that is, the effective LO is on the high 
side of the Omega signal or 10240 Hz is 
above 10200 Hz by 40 Hz. This is of no 
consequence since the subtraction to obtain 
the correct line of position direction can be 
reversed using complementary arithmetic. 

The 40 Hz output signal from the mixer 
is inherently noisy and also contains higher 
harmonics of the LO. A binary phase lock 
loop (BPLL) consisting of the 4030-4011 
and 4040 CMOS chips of figure 7, provides 
nine bits of filtering and a clean 40 Hz 
signal. The phase data contained in the 
40 Hz edges may actually be used at this 
point without any microprocessor by start- 
ing an RS flip flop with an 8 Hz edge 
obtained from the housekeeping timer and 
stopping with the next 40 Hz edge. The 
width of the resulting on-off pulse is directly 
proportional to the phase of the original 
10.2 kHz Omega signal with respect to the 
local clock which generates the 8 Hz ref- 
erence. A suitable counter, averaging, and 
subtraction circuit can be devised in hard- 
ware to measure Omega lines of position 
where the filtering time constant will be the 
width of the gating interval of figure 5, or 
about 8 Hz/5 for a bandwidth of 2 Hz. 

For microprocessor use we sample the 
cycling 40 Hz clock obtained from the rate 
multiplier and 8 stage counter of figure 7, 
with the 40 Hz Omega signal from the 
binary phase lock loop filter. An 8 bit three 
estate latch (4508) stores the individual 
Omega phase readings as 6 bit data and the 
other two bits of the latch are used to store 
the station status information from the 
gating circuitry of figure 7. These 8 bit 



Integrated Circuits for VLF-LF Receivers 



In our VLF-LF navigation 
lab at Ohio University we have 
found a great many standard 
IC chips useful for Omega 
(10 kHz range) or Loran-C 
(100 kHz range) receivers. 
Experimenters skilled in the 
art of fabricating high gain 
receiver circuitry might wish 
to substitute various other cir- 
cuits for the Mini-0 front end 
system. The following list of 
ICs has been used with both 
Omega and Loran-C systems: 

AM Receiver Chips 
(identical circuits) 
Fairchild uA720 
National LM1820 

RCA CA3123 

Signetics N546 

AM-FM-SSB Receiver Chips 
(not identical circuits) 
Fairchild uA721 
National LM373 or LM374 
Plessey SL1624C 
RCA CA3089 

FM Limiter-Detector Chips 
(used as envelope detectors 



by feeding input to limiter 
also to quadrature input) 
Fairchild uA721 
Signetics ULN2111 " 
National LM21 1 1 
RCA CA2111 



identical 
types 



FM Limiter Amplifiers 
(not identical circuits) 
Signetics ULN2208 
Signetics ULN2209 
National LM703 
National LM371 
National LM370 (AGC type) 
Fairchild uA757 (AGC type) 
RCA CA3028 

RCA CA3053 

There are probably others 
which would be suitable; refer 
to the manufacturer's litera- 
ture and application notes. 
One of the newest types, the 
Fairchild uA721, appears to 
work for both Loran-C and 
Omega receivers and has the 
potential for providing a noise 
blanker using the mixer stage, 
without adding any additional 
active circuitry to the front 
end. 



ADDED BUFFER CIRCUIT 




Figure 6: Use of the Sin- 
e/air "B/ackwatch" wrist- 
watch kit as a source of 
the 2? $ Hz reference sig- 
nal (32.768 kHz). This cir- 
cuit was used by the au- 
thor to provide both chro- 
nometer functions and 
Omega reference timing by 
mounting it in a plastic 
case so that the LEDs 
could be seen (see photo 
2). 



2'5Hz 
ALTERNATE REFERENCE 
CLOCK SOURCE 
(TO FIG 4) 



a 
b— I 



TO 

SEGMENTS 

OF WATCH < d ■ 

DISPLAY 

e - 

f - 

g • 



-*S+ 



TO DIGITS 

) OF WATCH 

DISPLAY 



CAUTION: 

SOME MODELS MAY HAVE 
SLIGHTLY DIFFERENT 
PINOUT NUMBERING 



V 



A7 



C NO.I IN SINCLAIR 
"BLACKWATCH" KIT 



77 



BINARY PHASE LOCK LOOP 



10.2 ZX 

INPUT 
(FIG 3) 



REFERENCE 
COUNTERS 




"A" TIME SLOT 
(FIG 4) 



GATE NO. 7 
(FIG4) 
[G7>- 



<jD SELECT FROM PROCESSOR ADDRESS DECODER, FIG 8 



B BIT 
} DATA BUS TO 
PROCESSOR 



D6 ON FOR A ONLY 

D7 ON FOR 625 ms OF EACH 
TIME SLOT 
4013 

MEASUREMENT 
WINDOW 
FLIP FLOP 



Figure 7: 8 bit processor interface. This is the interface used with the ]OLT 
or KIM- 7 versions of an M OS Technology 6502 in the author's laboratory. 
Vie address selection logic is shown in figure 8. The mixer and phase lock 
loop generate a 40 Hz difference frequency which drives the processor's 
interrupt line. This signal also provides the latching signal to the 4508 bus 
interface, so that when the processor responds to the interrupt it will have the 
data which was current at the time of the interrupt. The binary rate 
multiplier (4089) is used to divide the reference frequency to provide a 
crystal controlled clock into the reference counters, so that the count of 
crystal controlled cycles can be read following the interrupt. 



numbers now become the raw Omega data 
for processing and status using interrupt 
requests to the microprocessor at every 
40 Hz positive going edge. The data is used 
as if it were high order memory address with 
a decoder from the microprocessor address 
lines and output to the 8 bit data bus with 
appropriate software, figure 8. There are 
other ways of implementing the interface 
with about the same hardware depending on 
the particular microprocessor system used. 
If the 625 ms sample window of figure 5 
is used, then there are 25 Omega phase 
readings valid for each time slot. That is, 
there will be 25 cycles of the 40 Hz signal in 



625 ms. The microprocessor software de- 
signer can manipulate this data in various 
ways. Some receivers first estimate a mean 
or mode value. Many Omega processing 
systems create a software tracking loop 
which is similar in principle to a phase 
locked tracking loop as used in analog 
circuits. This can be done 'in the 40 Hz case 
by programming in increment-decrement ad- 
dition to the 40 Hz interrupt edge position 
such that the new calculated position will 
tend to be exactly at the same phase value 
for each reading. This estimate is stored in 
memory for each time slot creating what we 
would call a software memory aided phase 
locked tracking' loop. The loop output be- 
comes the phase of each time slot with 
respect to the cycling 40 Hz reference clock 
and is subtracted in pairs to generate lines of 
position. 

A microprocessor can be programmed to 
do this with 100 or so instructions. An- 
equivalent hardware memory aided phase 
locked loop and lines of position subtraction 
would require at least 20 additional inte- 
grated circuits as well as a memory. Thus the 



78 



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SELECTED 
WITH THESE 
INPUTS 




4049 
S. OUTPUT 

P>o-fi> 



TO 

DISABLE OF 
4508 LATCH 
(SEE FIG 7) 



UPPER 4 BITS OF 
MEMORY ADDRESS 



Figure 8: Part/a/ address 
decoder. In a small system, 
where only a portion of 
the total address space is 
actually used, it is possible 
to get away with partial 
decoding of addresses. 
This decoder lumps all ad- 
dresses of the form hexa- 
decimal 8 xxx together as 
the (single) address for the 
Omega interface; for sys- 
tems where memory ad- 
dress space utilization is a 
problem, other address de- 
coding con fig u rations 
should be used. 



Acknowledgments 

At Ohio University we have 
been developing low cost 
Omega navigation systems 
(ONS) for use by the general 
aviation community. The 
Mini-0 system described here 
is a spinoff of some of the 
simpler ideas. Part of the work 
reported here has been sup- 
ported by NASA Langley Re- 
search Center, Grant 
NGR 36-009-017, under the 
Tri-University Program in Air 
Transportation. The aid and 
support of Dr R H McFarland, 
Dr R W Lilley, Prof G E 
Smith, R J Salter, Lee Wright, 
Kent Chamberlin, Dan Moyer, 
and Ralph Smith are much 
appreciated on the project 
results. 



microprocessor can do this job as well as all 
the remaining computation to output some 
useful navigation information and still have 
space left for whatever the system designer 
wishes to do. 

At this point we leave it up to the 
software designer to implement a navigation 
system on the microprocessor. We have 
supplied raw phase data at a suitable low 
data rate (40 Hz), a collection of Omega 
sequence and time signals for interrupt and 
control of microprocessor functions, and 
means of identification of where the Omega 
sequence is at a particular time. The first 
stage in programming involves developing 
sensor processor filtering of the data down 
to the lines of position level. The simplest 
marine receiver might require only two lines 
of position outputs. Further sophistication 
would involve conversion to latitude and 
longitude, range angle, diurnal corrections, 
multiple frequency redundant systems, dif- 
ferential corrections, etc. The next article in 
this series, by Richard Salter of our labora- 
tory, presents some of the sensor software 
details. 

Test Equipment Recommended 

The Mini-0 receiver system is intended 
for fabrication by those skilled in modern 
electronic circuit arts. It is not recom- 
mended for the total novice. Access to some 
test equipment is required for alignment and 
checkout. An oscilloscope, preferably a trig- 
gered sweep model, a stable audio function 
generator, and a frequency counter with a 
quartz crystal time base, are suggested. 

The function generator should be capable 
of tuning the range of 5 kHz to 20 kHz with 
some reasonable stability (with an internal 
regulated DC supply) and a tuning rate such 
that the frequency of 10.200 kHz may be 
set to within a few Hertz. The adjustment of 
the very narrowband front end requires 
setting the function generator to the center 
frequency of 10.200 kHz and this should, be 
checked with the aid of a frequency counter 
operating in parallel or triggered from the 
function generator synchronizing output. We 
have used the EXAR model XR-2206KA kit 



(available from James Electronics, POB 822, 
Belmont CA 94002, for about $18 as a basic 
chip plus circuit board). This provides a 
convenient squarewave output for checking 
frequency in parallel with the sine wave 
output. A good quality logarithmic tuning 
potentiometer is required in these types of 
function generators. 

The frequency counter should have a 
10 second time base with a quartz crystal 
reference that is accurate to within ±1X1 0"^^ 
or has a low offset. If you do not have this 
item, many radio amateurs often use them in 
their shacks, as well as CB repair shops. 
Some frequency counters have provision for 
using an external time base which can 
provide the required precision for initial 
adjustment of the 32.768 kHz clock oscilla- 
tor. The Sinclair Blackwatch kit also has 
instructions for adjusting the offset using 
WWV time ticks on the high frequency 
(short wave) radio bands. This takes longer 
than using a good frequency counter but is 
adequate for the patient experimenter. For 
the experimenter who is involved with time 
and frequency measurements, a good 1 MHz 
secondary standard is suggested. Many oven 
controlled crystal oscillators are on the 
surplus market. (Herbach and Rademan, 
401 E Erie Av, Philadelphia PA 19134, has 
several with proportional oven controls in 
the $30 to $50 price range; a reasonably 
priced temperature compensated crystal 
oscillator is available from Bliley Electric Co, 
2545 W Grandview Blvd, Erie PA 16508, the 
model TCCO which requires 26 mA +5 VDC 
and costs about $75.) 

Some experimenters might even wish to 
consider the possibility of using an external 
1 MHz frequency standard as the micro- 
processor clock system so that all of the 
timing functions could be accomplished with 
precision using the microcomputer itself 
without ever using a special purpose Omega 
clock in the interface. 

When using an oscilloscope, it is suggested 
that most measurements be made with a low 
capacitance probe so that the waveform 
displayed will not be distorted by the lead 
capacitance to the scope. When observing 
the input signal at the preamplifier output 
terminal or at the input to the front end, an 
ordinary coaxial lead to the scope may be 
used because the impedance at this point is 
about 680 ohms. However, the output of 
many of the CMOS logic circuits is a much 
higher impedance, and distortion of the 
actual waveform will take place unless a low 
capacitance probe is used. The CMOS logic 
circuits will tolerate up to something like 
1 30 pF additional capacitance, but this can 
distort a 1 MHz signal." 



80 




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Continued from page 1 3 



attempting to sell the user the idea that 
the DEC PDP-8 that drove the reader 
would fit in the palm of his hand in a 
few years. The Intel 8008 was just out, 
and those outside the integrated circuit 
world could not understand its potential. 

In printers' terms the paper has a line 
screen of 25% density, similar to a 
printed photograph. All we did was to 
place the dots where we wanted them. 
To do this the RCA Vidiocomp was 
driven with our dot "font." The worst 
problem in producing the master was 
that the technicians adjusting the Vidio- 
comp did not really do a good job on the 
sweep linearity. It wasn't necessary in 
text, but it really came out in our reader. 
The data is encoded in a phase-like 
method where along the scan line the 
black dot is placed to either the right or 
left side of the cell, thus a black white or 
a white black. When scanned and con- 
verted to an analog signal, you have 
either a positive or negative transition at 
the cell center the same as many cassette 
tape recorders. This was done as we had 
just finished a cassette recorder design. 
The reader has a three cell scan head. 
Two cells track the line, and the third is 
the data cell. The organization is like a 
disk, where the first few lines at the 
beginning are a disk directory — in this 
case chapter paragraph line number 
starts. You can use the runout on each 
side to count your position the same as a 
disk head position encoder. 

If anyone wants more information 
please contact me, C R Conkling Jr, at 
POB 3 10, Shoreham NY 11786, 
(516) 744-9475. 

GRAY SCALE? 

I am following your series of articles 
on the optical bar code readers with 
great interest. Basically I agree with 
Messrs Banks and Sanderson (December 
1976 BYTE, page 12) that optical bar 
code readers and low cost printing will 
be "the way to fly." I would add that 
software would best be distributed as 
source code, although the technique 
could obviously be used for source or 
object code. I would suggest that the 
suggested format (figure 2, page 16) be 
enlarged to include a one byte "record 
type" code. This would allow for a far 
more flexible system at very small cost. 

I borrowed my son's (inexpensive) 
microscope and gave the sample bar 
codes (figure 4, page 17) a close look. 
One thing became quickly apparent: 
Even on the low density sample a lens 
system of at least 200X was required! 
Any less and I could see more than one 
bar at a time. Secondly, holding the 
paper flat to prevent misfocusing was a 
problem. The high density samples had a 
problem obvious to the unaided eye — 
the ink smeared (see copy enclosed). My 
experiment indicated that your sample 
(e) was about the best. Sample (c) came 
close, but might present problems in 
tracking. 



Several thoughts on the subject: 
Some form of audio feedback from the 
computer (have the processor make a 
"click" noise by toggling a one bit 
output port into a speaker) would help 
maintain the correct scan rate and tell 
when you had strayed off the track. 
Perhaps the bar code system is not the 
ultimate way to go; how about a "gray 
scale" — you could print white, 33% 
halftone, 66% halftone, and black (giving 
four levels) or what have you. The 
halftone system would allow printing of 
wider bars while yielding high bit 
density, thus reducing the requirements 
of the lens system. One final thought: 
With proper forethought, the bar code 
"pencil" could double as a "light pen." 

Please keep up the good work, espe- 
cially on this subject. I believe you are 
on to something very worthwhile. 

Carl K Zettner W5HFG 

108 Moss Dr 

San Antonio TX 78213 

As noted earlier (see January BYTE, 
page 7 J) the smearing of the high 
density samples and variability of the 
spacing rule out their use. The actual 
problem can be attributed to a nonuni- 
form! 'ty in the response of the photo- 
graphic preparation of the plates for the 
print run, since the smearing was seen in 
our "blueprint" proof copy of December 
BYTE. 

The magnification of the optics is not 
the problem; rather it is the aperture of 
the lens, and masking of that aperture so 
that only one bar width at a time is 
viewed. The slit method (see comments 
in another section of this forum) shows 
good promise as an inexpensive but quite 
usable form of optics for bars such as 
those we've printed in recent tests. The 
larger the area of the opening, the 
greater the amount of the bar which is 
sensed. The narrower the effective aper- 
ture (whether or not a lens is used), the 
higher the density can be made. 



NRZ, ANYONE? 

I was very glad to sec your article on 
bar coding, and I hope it will be a 
success. There are a couple of improve- 
ments I'd like to see, though. 

Since you're printing the bar code, 
won't you please print the same data in 
human readable form, too? The Uni- 
versal Product Code has the numbers 
printed. Punch cards have their prob- 
lems, but at least with them you can tell 
exactly, character for character, what's 
going into the machine. With paper tape 
(or your bar code formats) you can 
puzzle it out, but only with a lot of 
work. Of course, with magnetic tape 
there's no hope. You're suggesting 50 
bits per inch [not anymore] so you 
could print the corresponding hexa- 
decimal characters immediately below 
the bars at 12.5 characters per inch. (I've 
found 12 to 21 characters per inch in 
BYTE articles.) Of course, if you're 
printing ASCII characters, the characters 



themselves could be used instead. If a 
misprint keeps one frame of bars from 
being read, I'd sure rather key in 125 
hexadecimal characters than 500 pain- 
fully deciphered bits. 

Since bar codes can be the same as 
saturated magnetic tape codes, I'm sur- 
prised you didn't suggest the NRZ (Non 
Return to Zero) code. In it, the medium 
is divided into equal cells. A transition 
(from white to black or black to white) 
in the center of a cell represents a one, 
while no transition represents a zero. A 
transition also occurs at the end of every 
cell for timing. Although more difficult 
to read manually than your formats two 
or three, this code has even spacing and 
is more compact: 




If we assume, in each of these for- 
mats, that the short spaces and bars are 
half the width of the long spaces and 
bars, and that 50 bits per inch is a 
reasonable density for format 2, we can 
calculate the corresponding densities for 
the other formats: 

Density 
Format (bits per inch) 

1 75-150, average 100 

2 50 

3 50-75, average 60 
NRZ 75 

[We have to figure out how to do it 
first . . . but maybe . . . / 

I think the NRZ code with hexa- 
decimal or ASCII characters would be a 
good compromise. 

To encourage use of your bar code 
standard, BYTE could offer to convert 
data from tape to bar code for anybody 
at a standard price. That way other 
magazines, particularly those on small 
budgets like club newsletters, could use 
it. If it were only a few dollars a page, 
bar coding would be cheaper than cas- 
settes (though slower to read) even for a 
"production run" of half a dozen! 

Finally, a hard copy printer or even a 
typewriter can print a low density bar 
code: 010001101 can be scanned right 



82 









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down ihe center of the characters! (See 
Fred Howard's letter./ 

Keep up the good work. 

James R Van Zandt 

26Shelton St 

Nashua NH 03060 

Using software (al though this may be 
premature), NRZ may very well be much 
more complicated to decode. But it may 
be worth trying. Since the format of the 
Ugh t and dark we print has no bearing on 
the hardware, provided we use bars with 
physical minimum size parameters set by 
an aperture standard, it only requires a 
night or weekend's worth of software 
and some experiments with PC layout 
tape, white paper, a darkroom and a 
camera to try out a different format at 
the bit level. In actual program object or 
source code, we plan to print an exact 
hexadecimal map of each bar code 
frame, thus allowing both hand and 
machine readable data entry. 

SPACES CARRY NO INFORMATION? 

Harold Mauch sends us this commen- 
tary, which we print with a few words at 
the end: 

I would like to lake exception to the 
choice of proposed format for the 
"Machine Readable Printed Software" 
described on pages 12-17, BYTE maga- 
zine for December 1976. Of the three 
formats described, the selected format 
(format 3, page 14, figure I) has the 
least going for it. 

• It is lower density than formal I 
since the spaces carry no useful 
information. 

• Contrary lo the assertions of the 
author, the spaces provide only a 
marginal reference for discrimi- 
nating wide from narrow bars. 

• The hardware and/or software 
needed lo implement format 3 is 
more complicated than that 
required to read either format I 
or 2. 

Examinalion of the test strings on 
page 1 7 indicate ihe lypesetting, litho- 
graphic and printing process is far from 
"perfect" in maintaining bar to space 
ratios. To compensate lor this imperfec- 
tion, author Keith Regli added a "bias 
computation and adjustment" to ihe 
space couni, thus complicating the 
sofiware. 

Such ad hoc measures could be elimi- 
nated with format I. The printing proc- 
ess maintains excellent bar to bar and 
space lo space ratios, bin poor bar to 
space ratios. The lithographer may have 
over or under exposed the plate or the 
priming press may be running too much 
or too little ink. A more satisfactory 
approach for discriminating between 
wide and narrow bars is lo compute the 
average of known wide and narrow bars 
(add the counts and shift left once). This 
provides a discriminaiion threshold with 
which other bars in the local area may be 
compared. The same procedure would 



apply lo wide and narrow spaces. Even 
with ihe addition of reference bars and 
spaces, the average data density of for- 
mat 1 is 33% greater than format 3 and 
60% greater than format 2. 

While on the subjeel of reference 
bars, formal 3 needs them also. If the 
data is a siring of /.eros, I claim lhai the 
printing variations evident in the test 
strings on page 17 will eventually con- 
fuse the decoding algorithm. This can be 
resolved by adding a reference or pariiy 
bar, preferably lo each 8 bil byie. This 
required addiiion thus gives formal 1 a 
50% densily advantage over format 3. 

I presently use and prefer a signal 
conditioner circuit nearly identical to 
that described in author Merkowitz's 
article (page 81, figure 3). The super 
differentiator circuil of figure 4 is belter 
for low density waveforms since the 
photo sensor ouiput is nearly a square 
wave. However, when bar and space 
width is decreased to the dimension of 
the photo sensor's effective aperture 
(0.005-0.010 inch in my equipment), the 
photo sensor output looks more like a 
sine wave which does not differentiate 
into the narrow pulses required by the 
threshold comparator of figure 4. 

One final note: My experience is that 
timing bits alluded to in figure 2, 
page 16, are required, not for liming, but 
to permit ihe signal conditioner detec- 
tors lo stabilize. Referring to figure 3, 
page 81: When ihe pholo sensor is rest- 
ing on the white page before a line of 
code is scanned, the peak detectors will 
decay to ihe "white" level. This creates a 
severe white bias until the "black" peak 
detecior stabilizes. The result is lhat ihe 
measured duration of the first few bars 
and spaces of a line will be grossly 
distorted and not suitable for data. 

Harold A Mauch 

Director of Engineering 

PerCom Data Co 

4021 Windsor 

Garland TX 75042 

The point about format 1 versus for- 
mat 3 needs some comment. First, the 
format 3 spaces do carry useful informa- 
tion - they give the timing values 
needed to discriminate bit widths. The 
bias calculation is required also in for- 
mat 1, which will suffer from the same 
problems in the switching of the levels. 
(This problem is caused by the tendency 
of the system to take different amounts 
of time to change state from black to 
white than vice versa.) By using explicit 
black marks for each bit, at least we are 
guaranteeing that each bit has the same 
biases (one rising edge to black, one 
falling edge to white). We don't care 
about bar to space ratios other than the 
fact that they are locally constant within 
a space of several bits retained in the 
running average of the input algorithm. 

The startup bias also depends upon 
your detector design, and later conversa- 
tions with several engineers suggests that 
the circuits of Fred Merkowitz's articles 
are overly complex for this applica- 
tion ... CH ■ 



84 



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87 



COMPARATOR 



MICROPROCESSOR 
INPUT PORT 



COMPARATOR 



COMPARATOR 




Figure 1: Block diagram of 
an analog to digital con- 
verter. This diagram shows 
the functions of the var- 
ious components of the 
converter. There are two 
inputs to the tri state regis- 
ter, one from the com- 
parator and the other from 
the channel decoder. The 
input marked A is the out- 
put state control and the 
Input Enable Control line. 
The input marked B is the 
register input strobe line. 



POTENTIALLY 
16 

CHANNELS 
TO SELECT 



CHANNEL 
DECODER 



MICRO- 
PROCESSOR 
' OUTPUT 
PORT 



An Inexpensive Joystick Interface 



Thomas R Buschbach In the quest to develop the ultimate in 

12310 Purceii Rd video games, the need arose to interface 

Manassas VA 22110 analog controls to a microprocessor. A com- 

mon control used in most video games is the 
joystick. It allows you to control two axes 
with one device. A joystick usually has 
potentiometers mounted on two adjacent 
sides as shown in photo 1. The potentio- 
meters vary their resistance from ohms to 



Listing 1: This 8080 op code will read the digital value for the desired analog 
to digital channel. The digital value is left in the accumulator. All numbers in 
this listing and listing 2 are in octal. 






octal 
address 

000 
003 
005 
007 
010 
011 
013 



octal code 

076 XXX 

323 AAA 

333 BBB 

365 

227 

323 AAA 

361 



op 

MVI 

OUT 

IN 

PUSH 

SUB 

OUT 

POP 



operand commentary 



A, XXX 

AAA 

BBB 

PSW 

A 

AAA 

PSW 



A:= number of desired channel; 

output channel to unit AAA 

read digital value of channel from BBB 

save digital value; 

clear accumulator and flags; 

clear output port to 0; 

restore saved value; 



88 



their maximum value as the control stick is 
moved. The change in resistance is propor- 
tional to the displacement along the axis 
parallel to the surface the potentiometer is 
mounted on. All that remains is to convert 
these resistance values into digital values 
which the microprocessor can manipulate. 
To develop a full range of two and four 
player games, I decided four joysticks would 
be required. To interface four joysticks to 
the microprocessor would require eight 
channels of analog to digital conversion. 
Since the commercial analog to digital con- 
verters cost approximately $50, buying eight 
of them was prohibitively expensive. Even 
buying only one and multiplexing its inputs 
and outputs seemed to be more expensive 
than necessary. 

Being a typical software fanatic, I had no 
desire to build my own analog to digital 
(AD) converter. However, after examining 
all the alternatives, I decided to build Roger 
Frank's circuit (BYTE, May 1976, page 70), 







Photo 1 : This is a typical 
joystick showing the po- 
ten tiometers that are 
mounted on each side of 
the device and wired in 
parallel. 



which utilizes a digital to analog converter 
(DAC) and a software algorithm to do the 
analog to digital conversion. After ordering 
the required components I decided that 
using a software algorithm to do the conver- 
sion for eight channels of analog to digital 
conversion would not leave the processor 
time to process the game's algorithm. At this 
point I decided to implement the software 
conversion algorithm in hardware. 

In developing the circuit I had four design 
goals in mind: 

Interface at least four joysticks, eight 
channels analog to digital. 

Use no more than one input and one out- 
put port. 

Use no processor cycles for the conversion 
process. 

Sample each analog signal at least 1000 
times per second. 

A block diagram of the circuit is shown in 
figure 1 . The detailed functions of the digital 
to analog converter and the comparators are 
explained in Roger Frank's article men- 
tioned earlier. If you are considering con- 
structing this circuit, I would recommend 
reading that article. 

The circuit is controlled by a counter 
which continually counts down from 
octal 377 to 0, driving the inputs of a digital 
to analog converter. The output of the 
converter is compared to the analog input 
signal from the joystick. As long as the 
converter output voltage is higher than the 



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voltage from the joystick, the output of the 
comparator is 0. When the counter has 
counted down to a value which causes the 
converter to output a voltage equal to, or 
slightly below, the voltage from the joystick, 
the comparator output goes high. This edge 
triggers the corresponding tristate register to 
load the current value of the counters. This 
occurs asynchronously for each channel. 

To access the digital value for the desired 
channel, you output a number from 1 to 8, 
corresponding to the desired channel, on an 
output port. Leaving this value latched in 
the output port, the digital value may be 
read from the desired input port. Clearing 
the output port to completes the opera- 
tion. This operation is shown in listing 1. 

Figure 2 is the schematic to interface one 
joystick to the microprocessor. The circuit 
may easily be expanded to handle four 
joysticks. The 74123, IC1, is used as a 
multivibrator to generate a pulse waveform. 
With the resistance and capacitance values 
shown it will have a frequency of approxi- 
mately 0.3 MHz. This pulse train drives the 
count down input of the 74193 counters 
IC2 and IC3 which form an eight bit binary 
counter which continually counts from 
octal 377 (or hexadecimal FF) to 0. The 
outputs of counters IC2 and IC3 are tied to 
each tristate register pair (IC5 and IC6, and 
IC7 and IC8) and to the digital to analog 
converter, IC4. This latter circuit produces a 
negative ramp continually going from +5 V 
to V in 256 steps. The output of IC4 is 
converted from a current to a voltage signal 
by IC9. One quarter of IC1 is used to 
compare the output of IC9 to the voltage 
from the joystick. The output of each 
quarter of IC10 is tied to a single tristate 
register pair. This output remains a logical 
as long as the voltage from IC9 is greater 
than the voltage from the joystick. When the 
voltages are equal the output of the cor- 
responding quarter of IC10 shifts to a 1 . 
This edge triggers the corresponding pair of 
registers to latch the value of the counters at 



Table 1: Power connection table for the 
circuit of figure 2. 



Number 



Type 



+5 V GND -12 V +12 V 



IC1 


74123 


16 


8 


IC2 


74193 


16 


8 


IC3 


74193 


16 


8 


IC4 


MC1408L-8 


13 


2 


IC5 


74173 


16 


8 


IC6 


74173 


16 


8 


IC7 


74173 


16 


8 


IC8 


74173 


16 


8 


IC9 


LM301 






IC10 


LM339 




12 


IC11 


7442 


16 


8 


IC12 


7404 


14 


7 



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91 







Photo 2: Underside of 
finished assembly showing 
wire wrap board and two 
joysticks. 



Photo 3: This is the top view of the finished unit 
showing the two control sticks; the connectors are for 
input port, output port and power. An identical box 
with two more joysticks will plug into the side of this 
box for games requiring four joysticks. 



Listing 2: This subroutine will read the digital value from a requested analog 
to digital conversion channel, set minimum and maximum values, apply a 
scaling factor, add or subtract an offset value, and then return the resulting 
value in the accumulator to the calling program. The program can be located 
at any high order address, symbolized by <x> in the listing. 



octal 
















address 


octa 


code 


label 


op 


operands 


commentary 


000 


176 






MOV 


A,M 




A:= channel number; 


001 


323 


002 




OUT 


2 




output channel number; 


003 


333 


002 




IN 


2 




input digital value; 


005 


043 






INX 


H 




HL: = HL+1; 


006 


107 






MOV 


B,A 




B:=digital value; 


007 


227 






SUB 


A 


i 




010 


323 


002 




OUT 


2 


clear output port; 


012 


176 






MOV 


A,M 




A:=minimum value; 


013 
014 


270 
332 


020 <X> 




CMP 
JC 


B 
JP1 


) 


if B>A then go to JP1 [not lower limit] 


017 


107 






MOV 


B,A 




else B:=A [set lower limit] ; 


020 


043 




JP1 


INX 


H 




HL: = HL+1; 


021 


176 






MOV 


A,M 




A:=maximum value; 


022 
023 


270 
322 


027 <X> 




CMP 
JNC 


B 
JP2 


i 


if B<A then go to JP2 [not upper limit] 


026 


107 






MOV 


B,A 




else B:=A [set upper limit] ; 


027 


043 




JP2 


INX 


H 




HL: = HL+1; 


030 


227 






SUB 


A 




clear accumulator and flags; 


031 


206 






ADD 


M 




A:=A+scale factor; 


032 


372 


054 <X> 




JM 


JP3 




if scale factor negative then go to JP3; 


035 


312 


070 <X> 




JZ 


JP4 




if scale factor zero then go to JP4; 


040 


127 






MOV 


D,A 




D:=A; 


041 


170 






MOV 


A,B 




A: = B; 


042 


027 




JP5 


RAL 






shift left; 


043 
044 


067 
077 






STC 
CMC 




i 


clear carry; 


045 


025 






DCR 


D 




D:=D-1; 


046 


302 


042 <X> 




JNZ 


JP5 




if D*0 go to JP5; 


051 


303 


067 <X> 




JMP 


JP6 




go to JP6; 


054 


346 


177 


JP3 


AN I 


177 




mask most significant bit; 


056 


127 






MOV 


D,A 




D:=A; 


057 


170 






MOV 


A,B 




A:=B; 


060 


037 




JP7 


RAR 






shift right; 


061 
062 


067 
077 






STC 
CMC 




! 


clear carry; 


063 


025 






DCR 


D 




D: = D-1; 


064 


302 


060 <X> 




JNZ 


JP7 




if D is greater than go to JP7; 


067 


107 




JP6 


MOV 


B,A 




B:=A; 


070 


043 




JP4 


INX 


H 




HL: = HL+1; 


071 


227 






SUB 


A 




clear accumulator and flags; 


072 


206 






ADD 


M 




A:=offset value; 


073 


372 


100 <X> 




JM 


JP8 




if most significant bit =1 then go to JP8 


076 


200 






ADD 


B 




A:-A + B; 


077 


311 






RET 






return; 


100 


346 


177 


JP8 


ANI 


177 




mask most significant bit; 


102 


127 






MOV 


D,A 




D:=A; 


103 


170 






MOV 


A,B 




A: = B; 


104 


222 






SUB 


D 




A:=A-D; 


105 


311 






RET 






return; 



that instant. All tristate register outputs are 
normally in the high impedance state. To 
access a register you output the number of 
the desired channel on an output port. The 
7442, IC11, decodes the four least signifi- 
cant bits of the output port to determine 
which register pair to enable the outputs on; 
at the same time disabling the inputs of the 
register pair so that the registers will not be 
updated while the microprocessor is access- 
ing them. A on the output port places all 
tristate register outputs in the high imped- 
ance state. 

Construction Notes 

Resistor R4 is used to set the maximum 
digital value possible. Set all data inputs to 
the digital to analog converter at +5 V, then 
set R4 to yield the desired digital value. This 
sets all analog to digital converter channels 
simultaneously. If it is required to adjust a 
single channel's maximum value then a 
resistor must be added in series with the 
joystick, such as RI5. A value equal to the 
joystick's internal resistor would cut the full 
scale digital value in half. Note that the 
maximum value may also be limited by 
software as is done in listing 2, but this does 
not utilize the full displacement of the 
joystick, as using R1 5 would. 

The +5 V at the joysticks must be regu- 
lated and free from noise. Any fluctuations 
in this voltage will cause fluctuations in the 
digital value. Depending on your power 
supply and wiring, it may be necessary to 
provide a zencr diode for on board regula- 
tion o\' the +5 V supply. Also, be sure to use 
several bypass capacitors. 

Software Control 

The subroutine of listing 2 will read the 
digital value from the requested analog to 
digital conversion channel, set minimum and 
maximum values, apply a scaling factor, add 



92 









or subtract an offset value, and then return 
the resulting value in the accumulator to the 
calling program. 

A control block must be set up for each 
analog to digital channel. The address of the 
control block must be loaded into the HL 
register pair prior to calling the subroutine. 
The control block of 5 bytes must be in the 
following format: 



Starting 
address 
+1 byte 
+2 bytes 
+3 bytes 
+4 bytes 



Channel number 

Minimum value 
Maximum value 
Scale factor 
Offset value 



The first byte, channel number, selects 
the desired pair of tristate registers. It is the 
binary coded decimal number which when 
output to the analog to digital converter unit 
will cause IC1 1 to enable the desired register 
pair. 

The second byte, minimum value, deter- 
mines the absolute minimum number that is 
accepted from the converter. If the value 
from the converter is smaller than the 
minimum value it is set equal to the mini- 
mum value. 

The third byte, maximum value, deter- 
mines the absolute maximum number that is 
accepted from the converter. If the value 
from the converter is larger than the maxi- 
mum value it is set equal to the maximum 
value. 

The fourth byte, scale factor, determines 
by what power of two the raw digital data 
will be scaled. Scaling is accomplished by the 
new value set equal to the raw data times 2 
raised to the power of the scale factor where 
the scale factor is any value from —127 to 
+127. This yields the following possible 
factors (...8, 4, 2, 1, .5, .25, .125,...). A 
one in the most significant bit signifies a 
negative scale factor. 

The fifth byte, offset value, is added to 
the digital value after the scale factor is 
applied. It may be any number from —127 
to +127. As a two's complement integer, a 
one in the most significant bit signifies a 
negative offset. 

Conclusions 

The final assembly of this circuit, shown 
in photos 2 and 3, was built into an 
aluminum housing on a wire wrap board. 
The circuit can be used to interface any 
analog voltage signal to a microprocessor. 
The circuit for interfacing two joysticks to 
the microprocessor was constructed for 
about $35, exclusive of the cost of the 
joysticks. For an additional $10 the circuit 
could be increased to handle four joysticks." 




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93 



Continued from page 16 



Popular Electronics Cosmac ELF proj- 
ect, has a possibility of expansion with- 
out too much complexity. The processor 
was obviously designed with the notion 
that software is cheaper than hardware 
(sometimes) and the 1802 can be pro- 
grammed to replace hardware in many 
ways. 

One such way is using a program- 
mable output line as a memory exten- 
sion address bit. The processor has a Q 
line output which can be programmed 
in software to be either high or low. This 
could be used (properly buffered of 
course) as an address bit to select a page 
of memory. This would allow expansion 
of its address to 17 bits very simply and 
allow 128 K with very little hardware 
and also very little software. 

I don't intend to be even in the 64 K 
range for quite some time but those who 
could use 128 K now can get it easily. 
Thanks also for the "Beer Budget 
Graphics" article in the November issue, 
page 26. 

John Pawlicki 

£065 Greenwycke Ln 

Monroe Ml 48161 

The same general technique is what is 
meant by adding bank selection logic to 
a machine. Several processors have simi- 
lar opportunities for expansion. For ex- 
ample, the National Semiconductor 
PA CE 16 bit processor has 4 program- 
mable flag outputs - treating those flags 
as address bits externally results in a 
total of 20 bits worth of memory ad- 
dress space, or a maximum of 1 ,048,5 76 
words of memory. 

ARE ANY READERS USERS OF 
SURPLUS DATAPOINT MACHINES? 

I've been reading BYTE since the 
August 76 issue and have enjoyed it 
quite a lot. It is nice to know there are 
so many computer freaks out there. The 
reason I'm writing is that I used to work 
for Datapoint Corp as a technician. I had 
a Datapoint 2200 Version II to use for 
test purposes. It is an 8 bit TTL mini- 
computer and is fairly fast and powerful. 
It has a built-in 80 character by 12 line 
CRT display, a keyboard and a dual 
cassette deck. Although it has only 16 K 
of programmable memory, I found it 
more than adequate with the 2 cassettes 
with 110 K each, and disk operating 
software is available. There is a large 
amount of high level software (including 
timesharing) available including several 
excellent diagnostic programs (capable 
of identifying which memory chip is 
bad, for example). 

They have made over 5,000 of these 
minis since 1973 and they are available 
in the used market. I have read of 
amateur use of the PDP-8, but there has 
been no mention of the Datapoint. Is 
there anyone else out there interested in 
this mini? 

Bill Doyle 



A COMMENT ON 
BUG OF THE MONTH #4 

The solution to "Bug of the Month 
#4," in October 76 BYTE, page 41, 
overlooks an important point. I think it 
is logically correct after handling the 
N=2 case and moving statement K=1 to 
precede the last RETURN as suggested. 
However, the program (or any program) 
does not run in a clean environment. 
Any computer that a FORTRAN com- 
piler or interpreter runs on has a limited 
integer range. If the value of N to be 
tested is prime and near the maximum 
integer that can be represented, the 
computation 1*1 will result in integer 
overflow. This is particularly a problem 
in FORTRAN as some versions do not 
give error indications on integer over- 
flow. 

As an example, I checked this prob- 
lem using a version of WATFIV on an 
IBM 370. Integer overflows do not give 
an error. The maximum positive integer 
is 2,147,483,647 (2**31 -1). In the 
program the value of I is increased until 
1*1 is greater than N, assuming N is 
prime. The largest value of I which will 
not overflow when squared is 
SQRT (2147483647) truncated or 
46340. Any prime numbers larger than 
46340**2 (2,147,395,600), but still 
within the integer range, will cause an 
integer overflow of I and improper ter- 
mination. I consulted a prime number 
table and found they don't generally go 
up to 2 billion; however, there are prob- 
ably plenty of prime numbers in this 
category. 

Even in the case that an error mes- 
sage occurred on overflow, the routine is 
still not working correctly. While it 
would not result in potentially erroneous 
results, neither has an answer been re- 
turned to a perfectly reasonable request. 
For these large values of N, a possible 
solution is to simply check for the value 
of I exceeding 46340 following the I 
increment. If this occurs, N is then 
prime. 

Unfortunately, this requires an extra 
operation in the loop and depends upon 
the computer's integer range. I have not 
been able to think of a better method. 

Keep up the good work. "Bug of the 
Month" is usually interesting. 

Richard Altmaier 

POB 2061 

Stanford CA 94305 

CORRECTIONS FROM BOB MARSH 

Three factual errors were included in 
recent issues of BYTE magazine regard- 
ing Processor Technology products: 

1. Our Software No. 1 Resident Assem- 
bler, Editor Monitor package (referred 
to in the article as "SYS 8") was a 
joint development effort between 
Microtec and Processor Technology. 
Employees of PTC added many neat 
features to the original Microtec 
program in order to produce Software 
Package No. 1. It was first distributed 



in July or August of 1975 in the form 
of well documented source listings. 
Paper tapes were distributed to many 
computer clubs free of charge. 
Other companies, including IMSAI 
and Tarbell, have since made use of 
Software No. 1 adding minor modifi- 
cations to suit their 10 device 
requirements. To my knowledge at 
least six other firms have reproduced 
Software No. 1 in one form or 
another, all of them giving PTC and 
Microtec credit for authorship. (All, 
that is, except one rather well known 
"surplus" dealer.) Please note that 
Microtec receives a small but well 
deserved royalty on each Software 
No. 1 we distribute. No other 
manufacturers are paying such royal- 
ties. 

Software No. 1 is currently available 
from Processor Technology for 
$14.50 including both source listing 
and hexadecimal object paper tape or 
CUTS/BYTE standard cassette. 

2. A recent review of our VDM-1 Video 
Display Module stated delivery as 60 
days.. In fact VDM-ls have been 
available "off-the-shelf" since October 
of 1 976. There is no excuse for any of 
our 40 or so retail distributors to be 
out of stock for more than a few days. 
With good planning they should 
always have VDM-ls, as well as our 
2KRO, 3P+S, 4KRA and 8KRA 
modules, in stock. 

3. In your review of the Sol computer 
system you added $97 for our CUTS 
audio cassette data interface. The Sol 
has its own CUTS type interface built 
in and does not require an additional 
module for this function. (The CUTS 
board is primarily used in Altair and 
IMSAI mainframes.) So the system 
pricing in your example should be: 

Sol-20 kit $ 995 

SOLOS module 100 

TV/monitor 150 

Cassette recorder 100 

8KRA 295 

Software 48 

$1688 

Bob Marsh 
Vice President 

Processor Technology 
6200 Hollis St 

Emeryville CA 94608 

COMMENTS ON HOME COMPUTERS: 
FIND A NEED AND FILL IT 

Find a need and fill it! Henry Kaiser 
built quite a business organization using 
that phrase as one of his business pre- 
cepts. And now the development of 
microcomputers and microprocessors has 
created a market for home use. 

There are many functions in the 
home that can be carried out by micro- 
computers because of their unique 
properties that could not be effectively 
performed before. They include financial 
information, inventory of assets, in- 
ventory of food and supplies, energy 
control, recreational games and surveil- 



94 






lance for theft and fire. You can prob- 
ably think of more uses. 

A whole new industry is being 
spawned and it does not detract from 
other industries because new needs are 
being created. It can create new job and 
career opportunities for persons familiar 
with computer usage. 

What should be the marketing effort? 
Should it be structured like the auto 
industry with franchisee dealers and new 
models coming out every year or should 
it be structured like the radio and 
television industry with dealers carrying 
a multiplicity of models? Time will tell. 

1 would like to see demonstration 
models placed in places like Newport's 
Fashion Island or Glendale's Galleria or 
Los Angeles' Broadway Plaza. 

W Donald Pollock 
149 S Burlington Apt 2 
Los Angeles CA 90057 

WANTED: HIGH BANDWIDTH 
TV MODS 

I see many articles and projects on 
converting televisions to video terminals 
for use on minis and micros. Unfortu- 
nately (for me), these are all set up to 
generate a 32 character line. I would like 
to build a terminal using a TV or video 
monitor that would have 80 or 72 char- 
acters per line. Isn't there a kit or some 
way of bypassing the front end of a TV 
that will let you get the bandwidth 
needed? And just how does one figure 
out the bandwidth that is needed? Does 
anyone out there have the schematics or 
logic diagrams for such an adventure? 
Any help is really welcome. 

Joe Heck 

12 Enfield St 
Jamaica Plain MA 02130 

Any authors out there engineering a 
commercial TV mod which fits this bill? 
Or is it even possible? 

AUTHORS TAKE NOTE: 
488 BUS INTERFACE WANTED 

I have never written to a magazine, 
but as I have never enjoyed a publication 
as much as BYTE, I felt I just had to sit 
down and let you know how I feel. 

I got into programming in a small 
way a few years ago, with the HP-65 and 
programming became a new love. I am 
the Electronics Section Supervisor of the 
Metrology Laboratory at Puget Sound 
Naval Shipyard. We have recently ac- 
quired an Altair 8800a with 20 K pro- 
grammable memory, a TTY, 8 K and 
extended BASIC, and a 4P IO board 
with 4 ports. We are presently using the 
Altair for data processing and scientific 
calculations, but hope to use it in the 
future as an automatic instrumentation 
controller. 

This brings up a point: I sure would 
like to see marketed or published a 
design for an interface from the Altaic 
bus or standard 8 bit parallel ports to the 
IEEE 488-75 bus. The use of a micro- 



I 
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So experiment. Design. Test. 
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95 






computer and a terminal with this inter- 
face would give the calibration instru- 
mentation industry an inexpensive and 
versatile automatic test system. 

Bruce O Ferland 

PS: Am very excited about machine 
readable, printed software (bar codes). 
Hope to see some hardware marketed in 
the near future. 

FREEDOM OF ENTRY 

Wilber and Fylstra's sneers at com- 
puter professionals in the article "Home- 
brewery versus the Software Priest- 
hood," October BYTE #14, page 90, 
are both unnecessary and unsupported. 
To believe that the industry, its mana- 
gers, or its programmers encourages the 
present high cost of designing and main- 
taining software is stupid. Manufacturers 
normally lose money on systems soft- 
ware that they must develop to sell their 
machines and want lower costs and 
greater flexibility reliability (how much 
does a new release of an operating 
system cost?) more than anyone. The 
wide acceptance of such new techniques 
as top down structured programming, 
proofs of program correctness, chief 
programmer teams, and relational file 
organization indicates the interests of 
the profession in improving clarity, reli- 
ability and productivity. 

The demand for computers and pro- 
grams is very elastic (total spending lor 
these things increases as prices drop). I 
and other programmers have more work 
than we need. We are happy to have 
people learn programming. 

For those who did not see the article, 
Wilber and Fylstra accused the pro- 
fession: 

1. of deliberately surrounding com- 
puters with an aura of mystery; 

2. of protecting their privileged posi- 



tions by keeping their knowledge 
to themselves; 

3. of regarding their knowledge as 
sacred and beyond the non- 
specialist; 

4. of being high priests and acolytes 
of the holy alliance of logic. 

All of these charges are false. 

In its growth and achievements, the 
computer industry has been the most 
dynamic enterprise in this country. We, 
the computer hobbyists, exist because of 
this success, not in spite of it. Both 
politically and psychologically, the com- 
puter industry is remarkably free of 
barriers to entry. I have no license or 
certificate. I have no college degree yet. I 
was able to gel a position as a program- 
mer analyst with no previous experi- 
ence largely because of my experience in 
home computing. 

Wilber and Fylstra are idiots. They 
get a minus infinity on BOMB from me. 

The December 1 976 BYTE was one 
of the best ever. Keep up the (usually) 
good work. 

Martin Buchanan 

2040 Lord Fairfax Rd 

Vienna VA 22180 

See Mike and Dave's comments in 
their letter replying to H T Gordon's 
comments in December. They apply 
equally here. Would anyone else care to 
comment? 

IS THE SOFTWARE 

PRIESTHOOD CONCEPT 

CONSIDERED DANGEROUS? 

In his letter concerning the evalu- 
ation of microprocessor instruction sets, 
December 1976 BYTE, page 50, HT 
Gordon misunderstood the main thrust 
of our article, "Homebrewery versus the 
Software Priesthood," October 1976 
BYTE, page 90: Of course professional 



software people will a/ways be needed 
by business executives to help evaluate 
commercial products — that's not our 
point! We decry only those software 
people who, like some priests, seek to 
protect their knowledge of the program- 
mer's art, as opposed to their product. 
We were concerned with the personal 
market, not the very different commer- 
cial market, and we fundamentally wish 
to encourage widespread software liter- 
acy and free exchange in this personal 
computing hobby. 

Our recognition that there is room 
for journeyman programmers in the 
computer business should be clear from 
our discussion of their relation to the 
personal computing user. It is important, 
however, to carefully distinguish the two 
worlds. In the business world, the pro- 
grammer's relationship to the client is 
typically that of an employee or a 
contractor. By contrast, the firm sup- 
plying software for personal use hopes to 
have a large number of individual cus- 
tomers. The salient distinction is of 
accountability: The parties to a software 
transaction are much more closely re- 
lated in the first case than in the second. 
A commercial client can reasonably ex- 
pect the software product to suit its 
intended application, but any individual 
user of commercially supplied "per- 
sonal" software represents only a liny 
portion of the supplier's iniended mar- 
ket. Point one: Individuals warning per- 
sonal computers responsive to their own 
needs must be prepared to program the 
computer themselves. 

On the other hand, if a lot of people 
know how to program their own com- 
puters, then somebody else stands to 
lose. That somebody else, though, hardly 
includes everyone paid to write com- 
puter programs. While people won't buy 
something they could easily do better 
themselves, ihey are generally happy to 



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pay for quality merchandise. The essen- 
tial factor here is the quality of the 
product. If individual users find it easy 
to produce fairly good programs, they'll 
only buy the really good stuff; the only 
losers will be the producers of mediocre 
goods. On the other hand, if ignorance is 
rampant, the less competent pro- 
grammers can flourish in the personal 
market. Point two: Only the second rate 
practitioners stand to gain by a lack of 
wide scale diffusion of software skills. 

Now, most hackers learned what they 
know for free, and they learned it 
through personal contact with other 
hackers. This has almost always hap- 
pened where they were in close prox- 
imity. However, hobbyists, who cur- 
rently represent almost the entire com- 
munity of people making personal use of 
computers, are dispersed geographically. 
A good system of communication is 
necessary to bridge the distances. Tele- 
communications, with its very high 
transmission speed, can do wonders in 
helping people share consumerist views 
of the market as well as actual programs. 
The telephone brings personal tele- 
communication into a fantastically large 
proportion of people's homes, but it has 
the disadvantage of requiring both 
parties to a communication to be at 
home and disposed to communication at 
the same instant. That's why we pro- 
posed a network of "Community Infor- 
mation Exchanges" to serve as buffers to 
communication. Point three: A CI E net 
can be of immense utility in dispelling 
ignorance. 

To close the circle, we had no inten- 
tion to put anybody down; the ideas 
we're pushing are that a lot of people 
should learn to use computers well. 
That'll benefit all the good guys; and 
there's a plausible sounding mechanism 
by which we can pull it off. We disparage 
only those who, for whatever reasons, 
try to prevent it. 

Mike Wilber 

920 Dennis Dr 

Palo Alto CA 94303 

David Fylstra 

POB 10051 

Stanford CA 94305 

One point of information, which was 
not available to Mike or Dave, or Martin 
or H T Gordon at the time of writing of 
their respective letters: The results of a 
recent survey of a random sample of 
BYTE's 2100 readers out of our list 
show that they tend to be people with 
some experience in software with the 
folio wing numbers: 

51% indicated prior experience with 
any large computer system. 

58% indicated prior experience with 
a minicomputer. 

79% indicated that they intend to use 
(52%), or are using (27%), their 
personal computer system for 
software development. 

The numbers for various specific profes- 
sional and business applications goals 



such as text editing, accounting, or 
simulation were typically 30% in the 
"intend" category with 5 to 10% indicat- 
ing the "actually using" category. 

This tends to indicate a significant 
overlap between professional people and 
personal computing users so the issue 
may be a moot one. 

WHAT'S AN APPLE? 

I am thinking about purchasing an 
Apple II minicomputer, but before I 
purchase it I would like to get as much 
information as possible about it. I 
wondered if you have heard about this 
computer or if you had written a prod- 
uct description about it in a past issue. 
If you could send me any information 
on it, I would appreciate it very much. 

Andrew McNelly 

1176 Berkshire Dr 

San JoseCA 95125 

/ saw the prototype in operation 
on Saturday November 20 1976 in Palo 
Alto CA in my hotel room when Steve 
Jobs and Steve Wozniac, Apple 's creators, 
demonstrated it. It will be an excellent 
product, completely preassemb/ed, avail- 
able at computer stores nationally as 
well as by mail order. A 6502, 6 K ROM 
BASIC, color graphics, completely 



assembled case and keyboard, 4 K pro- 
gram memory, audio interface, monitor 
program, etc, all for about $1300. Go 
to a Homebrew Computer Club meeting 
and ask people about it. . . CH 

HIGH LEVEL DECODING PROBLEM? 

Thank you! 

As an owner of the SR-52 (and 
printer), I was delighted to see your 
articles in the December issue. Program- 
mable calculators, such as the SR-52 and 
HP-95/97, represent very powerful tools 
when one must deal with number 
systems. 

I've just about finished a mini Star 
Trek game. Each time you get a Klingon, 
the display flashes "BLOOIE" (310078, 
upside down). 

I hope you continue to set aside a 
small portion of your magazine for these 
hand held computers. 

Meanwhile, my Motorola 6800 evalu- 
ation board is waiting in the wings for 
an RS-232 peripheral. 

Tom Handley 

New Age Communications 

Portland OR 

R6: You can reprint this letter if 
you can decode my terrible writing. 
(No software provided!) ■ 



If you want a microcomputer 
with all of these standard features . . . 




• 8080 MPU (The one 
with growing soft- 
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• 1024 Byte ROM 
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• 1024 Byte RAM 
(With maximum 
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• TTY Serial I/O 

• ElA Serial I/O 

• 3 parallel l/O's 
•ASCII/Baudot 
terminal com- 
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• Monitor having load, dump, display, insert 
and go functions 



• Complete with card 
connectors 
• Comprehensive 
User's Manual, plus 
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• Optional ac- 
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display, audio 
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interface, power supply, ROM programmer 
and attractive cabinetry . . . plus more options 
to follow. The HAL MCEM 8080. $375 



.then let us send you our card. 



HAL Communications Corp. has 
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The MCEM-8080 microcomputer 
shows just how far this leadership 
has taken us . . . and how far it 
can take you in your applications. 
That's why we'd like to send 
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board that we feel is the 
best-valued, most complete 



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tested. Send for complete details. Or 
for fast action, Call 201-681-8700. 

Mosrerchorge and BankAmericard accepted. COD with 
1/0 deposit. NJ. residents add 5% sates tax. Price does 
not indude shipping and handling. 

Dealer inquiries invited. 



P.O. Box 386, Freehold, NJ. 07728. 
Phone- 201-681-8700 



What's 









^ 






• •• 

■ *0 CI 


i 






J 


MICRO DESIGNS 


100 





At Last! A Phi Deck Tape Mass 
Storage System for the 
Altair Bus 

Recognizing the .need for low cost 
versatile mass storage for the Altair and 
compatible 8080 based microcomputers, 
Micro Designs is offering two new digital 
cassette mass storage systems with up to 
one megabyte capacity. 

According to the manufacturer, an 
integral part of these ready to use 
systems is a complete system of file 
management software which allows the 
user to manipulate both symbolic and 
binary files with high level commands. 

The Micro Designs Model 1 00 is a 
compact single cassette drive which 
stores up to one half megabyte of data. 
The random access format of the data on 



the tape allows programmed access to 
any single 1 28 byte record. The data 
transfer rate is 1 000 bytes per second, 
and the tape may be searched at a rate 
exceeding 1 20 inches per second. The 
dual transport Model 200 puts up to one 
megabyte of peripheral files on line. 

Both units come fully assembled, and 
ready for immediate use. The interface 
board plugs into the main frame mother- 
board connector to attach the mass 
storage unit to the computer. To bring 
up the operating system, the user loads a 
cassette, and transfers control to the 
ROM on the interface board; all further 
tape operations are automatic. Status 
lights inform the user of relevant tape 
conditions, and hardware error detection 
is provided. These small table top units 
sell for $550 (Model 1 00) and $825 
(Model 200). Delivery is quoted as 
30 days after receipt of order. Contact 
Micro Designs Inc, 1175 Colusa Av 
Berkeley CA 94707.- 



At Issue, a Table 

We received the following item concern- 
ing a new products item in the December 
1976 BYTE. 

I wish to take issue with the compari- 
son chart given in the "State of the Art 
Disk Technology" on the SA-400 Mini- 
floppy. Specifically, the specifications 
on the 3M Minicartridge. When used 
with the Qantex Model 200 MINI- 
DRIVE™, the 3M Minicartridge has an 
unformatted capacity of 336 kilobytes. 
With the high density option, the Model 
200 will provide 676 kilobytes on one 
3M Minicartridge. These numbers are 
computed as follows: 

Capacity per track (unformatted) 
= Length of tape (feet) • 12 inches 
per feet • Packing density (bpi) 
8 bits per byte 

= 140 -12 -«20 
8 
= 168 K 
For two tracks 

Capacity = 336 kilobytes 
Thus, your figure of 100 kilobytes is 
completely erroneous. 

The Qantex Model 200 is offered 
with either a 1 or 2 track head. 

Next, let's consider transfer rate, 
which is computed as follows: 

Transfer rate = tape speed (inches/ 

seconds) * packing density 

(bits/inch) 

Transfer rate = 30 ips • 800 bpi 

Transfer rate = 24 kilobits per 

second 



Thus, an order of magnitude error in 
your chart. The Qantex Model 200 with 
the high density option provides a trans- 
fer rate of 48 kilobits per second. 

Average access time is usually com- 
puted as one half the time required to 
traverse the media. The Qantex Model 
200 provides a high speed mode wherein 
tape is moved at 90 ips. Access time is 
computed as follows: 

Tape length (ft) • 12 in/ft 



Access Time 



2 • Tape speed (in/sec) 
140 • 12 



Access Time 

2 • 90 

Access Time - 9.34 sec. 

The Qantex Model 200 MINI- 
DRIVETM w jth intimate electronics is 
significantly smaller than indicated, with 
a physical size of 4 by 4.1 25 by 3 inches 
with a companion PC card of 4.5 by 
6.5 inches. When packaged in an 
optional sheet metai enclosure, the com- 
plete drive including all PC cards is 4.75 
by 4.75 by 7.5 inches. 

Incidentally, the Qantex Model 200 
configuration, which is equivalent to the 
type supplied by the SA-400, also costs 
$390, quantity one. 

All things considered, I believe the 
decision to use a cartridge or disk must 
be founded upon careful analysis of 
system requirements. If access time is of 
key importance, the disk is the obvious 
choice. If capacity is of key importance, 
then the cartridge is the obvious choice. 
Other considerations might be the length 
of time it takes to validate a data block 



98 



just recorded. The rotational latency for 
the disk is 200 ms. Thus, the system has 
to wait 200 ms to validate a block just 
recorded. The Qantex Model 200 with 
a dual gap head will provide verification 
5 ms after the last bit has been recorded. 
For many applications, this is a critical 
parameter. 

Also to be considered is the MTBF of 
the two devices. The Model 200 MINI- 
DRIVE ™ has only one motor as op- 
posed to two for the floppy. Aside from 
the one motor, there is virtually no other 
mechanism for the Minidrive. The floppy, 
on the other hand, has the indexing 
mechanics to impart linear motion to the 
head positioning mechanism. Shugart's 
method for indexing is very clever; how- 
ever, it does not appear to be able to 
operate in an environment of moderate 
shock and vibration. Qantex experience 
in producing the "standard" 3M Car- 
tridge peripheral (AN/USH-26(V) for the 
Naval ElectronicsSystems has resulted in 
a cartridge drive which can operate in 
severe environments. 

Joel A Kramer 

President 

Qantex Division 

North Atlantic Industries Inc 

200 Terminal Dr 

Plainview NY 1 1803 

Moral of the Story: 

When putting in a new product item, 
the information is supplied by the 
producer of the product. Now, here is an 
oblique way of providing a new product 
item on the Qantex Model 200 MINI- 
DRIVE— in the way of an interesting 
letter of protest over a table found in 
December BYTE. As noted in the 
Shugart feature in December, the in- 
formation, in the table on page 87, was 
"supplied by Shugart." A note of 
qualification concerning the Philips cas- 
sette drive was placed in the text because 
of the availability of the Phi-Deck and 
similar low cost drives. 

Manufacturing and marketing a prod- 
uct, any product, whether it be a 
computer, or one's personal services, is a 
very personal and people oriented 
activity. Products don't spring forth by 
magic but represent the creativity of the 
people working on their design and 
marketing. This letter emphasizes that 
fact. . . CH ■ 



Where to Go to Get Whatever . . . 

The following text is taken essen- 
tially verbatin from a well written press 
release . . . 

A new directory has just been pub- 
lished that helps radio amateurs, CBers, 
experimenters and computer hobbyists 
locate equipment, parts, supplies and 
services. Over 600 sources of standard 
and hard to find gear are listed in the 
handy guide. Many of the 600 sources 
are mail order firms and many are 
discounters, too. All are firms that do 
business with electronics hobbyists. 

The first section of the book lists the 




firms alphabetically, their complete mail- 
ing addresses and phone numbers. Then, 
a list of the products or services they 
offer are provided along with key prod- 
uct information, minimum order 
amounts, shipping charges, etc. You'll 
find everything from the million dollar 
mail order firm that handles hundreds of 
product lines to the weekend garage 
operation offering a low cost accessory 
for a microprocessor or Citizen's Band 
transceiver. 

The second section of the book is a 
breakdown of products and sources in 
over 200 categories. Under each category 
is a listing of all firms that sell or 
manufacture the items cross referenced 
to the first section. For instance, there 
are over 25 sources of low voltage 
(12.6 VDC to 13.8 VDC) power supplies 
and over 50 sources of digital ICs. 

The buying guide contains many 
prices and sufficient detail that you can 
make your purchases directly from the 
book or obtain additional information to 
make your choice. Catalog prices, if any, 
are listed. 

The last section of the book includes 
all sources by state so you can buy from 
the firm nearest you when there are 
several choices. You'll probably find 
some local firms that you didn't know 
existed. 

The Underground Buying Guide is 
available only by direct mail from Penin- 
sula Marketing Services, 12625 Lido 
Way, Saratoga CA 95070. The price is 
$5.95 plus $.55 postage and handling. 
Californians add $.39 sales tax. Money- 
back guarantee within 10 days if you are 
not completely satisfied." 



Attention Commercial and Industrial 
Users of the 8080 

muPro Inc, 424 Oakmead Pky, 
Sunnyvale CA 94086, has just an- 
nounced what may be one of the best 
8080 oriented assemblers to come to 
market. This is the BSAL-80 assembler, a 
"block structured assembly language" 
which comes with a relocating and link- 
ing loader. Finally, someone in the 
microprocessor world has gotten around 



Microcomputer 

QuaydOAl 

does much more 

with the Z-80. 



©uaif 



This dynamite new microcomputer 
system in a kit moves data like nothing 
else on the market. Run it alone or 
plug it into an Si 00 bus Altair/IMSAL 
For solo performance, all you need is 
"QVi unregulated power supply and an 
I/O device. Plugged in, Quay 80Ai is a 
CPU, ROM, SIO, and RAM board—run 
any 5100 compatible device. BUT 
MORE THAN THAT. Quay 80AI's Z-80 
CPU opens challenging new areas of 
personal computing. 

Features 

D 51 00 bus compatible. Plugs in one slot of 
your Altair or 1M5AK 

D Z-80 w/2.5 MHz clock. 

D 1 K static RAM. 

□ 512 byte (ROM) monitor. Comes up 
running. Inspect, alter, dump, and load 
memory; ser breakpoint; jump to user 
program. Handles serial I/O or keyboard 
input, including setting baud rate, 

D 4 UVEPROM (2708) sockets. 

D Serial I/O. RS-232 and 20 ma interface. 

D Parallel keyboard input. Accepts stan- 
dard ASCII keyboard. 

D UVEPROM programmer. Program 2708 
type UVEPROMs. 

D 2 phase clock and sync. Run 51 00 com- 
patible peripherals. 

D 1 58 instructions. All 78 3080 instructions 
plus 80 new powerful instructions. 

□ On board voltage regulators. 

Quay 80AI in a kit is $450; factory as- 
sembled, $600. Send for complete 
details. Or for fast action call 201- 
681-8700. 

Masrerchorge and BankAmericard accepted, COD with 
1/3 deposit. NJ. residents odd 5% soles tax. Price does 
not include shipping and handling. 

Dealer inquiries invited. 



P.O. Box 386, Freehold, NJ, 07728 
Phone: 201-681-8700 



99 






to implementing some of those nice 
things which systems programmers have 
grown accustomed to on the bigger 
minicomputer and large scale computers! 
This product, according to the press 
release, "allows the user to write pro- 
grams in a high level language syntax 
while retaining the flexibility, program 
size and execution speed of assembly 
language. The ability to utilize any of 
the 8080 machine instructions and to 
control the use of the architectural 
features of the 8080 is maintained." 

Since the output is truly relocatable 
and has linkage information, the pro- 
grammer is able to develop truly modu- 
lar programs. The company also has 
available a line number oriented editor 
program and a loader program to go with 



the assembler. The product is definitely 
aimed at commercial users, since its price 
is well out of the range of the individual 
user on a tight budget: The BSAL-80 
assembler with BSAL-80 relocating/ 
linking loader are available together for 
$975 in 8080 resident form: the 
BSAL-80 text editor is available for 
$350. The text editor, assembler and 
loader are available as a package for 
$1250 and a FORTRAN IV cross 
assembly version is available for $1250. 
The 8080 resident versions are provided 
free of charge with the purchase of the 
muPro-80, muPro-80E or muPro-80ED 
hardware and software development 
systems manufactured by the firm. 
Delivery of the software is quoted as 
immediate." 



Cogitate then Emulate with 
This Bipolar Controller . . . 

The new Signetics 8X300 bipolar 
microprocessor device is now available in 
a single board design evaluation kit 
intended to titillate the fancies of the 
hardware designer . . . but guaranteed to 
find its way into a few homebrew 
experimenters' hands as one of the 
cheapest, fastest and easiest routes to a 
high performance microprogrammable 
emulator for existing or experimental 
processor architectures. At $299 it's 
hard to argue with the features of this 
kit: 



250 ns bipolar 8X300 processor. 
This processor handles 8 bits at a 
time with a read-modify-write 
cycle of 250 ns. (Yes, that's four 
instructions per microsecond!) 
256 bytes of high speed working 
data storage. (In the use of this 
board as a microprogrammed 
emulator, this becomes the area 
used for the control data and 
general registers of the machine 
you emulate. If you're crazy 
enough to want to emulate a 360, 
for example, allocate 64 of these 



bytes as the 16 general purpose 
registers and another 32 bytes for 
the four floating point registers 
and use the remainder for control 
registers and pointers within the 
emulator.) 

• Four IO ports implemented to 
interface external devices. (You'd 
use these ports to drive the 
address and data buses of the 
emulated computer system.) 

• System development software in 
PROM to aid you in utilizing the 
board. 

• 1 3 bit address bus and 1 6 bit data 
bus for the microprogram mem- 
ory used to drive the 8X300. 
(This should be more than enough 
control store to build the afore- 
mentioned 360 emulator. For a 
microprogramming project you'd 
want to add up to 8 K by 16 bits 
of dual port programmable mem- 
ory to this bus.) 

• Diagnostic and instructional con- 
trols which include a WAIT mode 
to allow single step operation, 
oneshot instruction jamming, 
ability to change or examine 
internal registers, etc. 

Contents of the kit (hardware) include 
an 8X300 processor, eight 82S116 pro- 
grammable memories for the data store, 
two 82S115 512x8 PROMs with the 
systems software for evaluation use, 
miscellaneous TTL parts, the printed 



How to Use the 8X300 Controller as an Emulator 



notes by Carl Helmers, Editor 



CHOOSE MULTIPLES OF 8 BITS 
FOR ADDRESS AND DATA BUS TO 
MAIN MEMORY MODULES OF THE 
EMULATED MACHINE 



8X3001O PORTS USED AS BUS INTERFACES FOR THE EMULATED 
COMPUTER SYSTEM'S ARCHITECTURE 



8X300KT100SK 

EVALUATION 

BOARD 



CONTROL 
LINES TO 
8X300 



777/5 figure shows the conceptual 
design of an emulator system built 
around your present microprocessor and 
the 8X300KTW0SK kit of Signetics. 
The parallel IO ports of the general 
purpose microprocessor are used to 
address and load the programmable con- 
trol store of the emulator (which you 



13 LINES OF CONTROL STORE ADDRESS 



16 LINES CONTROL 
PROGRAM DATA 



STATUS 
LINES FROM 
8X300 



PROGRAMMABLE 
CONTROL STORE 
<UPT0 8 K BY 
16 BITS. HIGH 
SPEED MEMORY) 



CONTROL 
STORE 
ADDRESS SWITCH 



16 LINES 
DATA FROM 
CONTROL 
STORE 



16 LINES 
DATA TO 
CONTROL 
STORE 



EMULATOR DEVELOPMENT PROCESSOR INTERFACE THROUGH PARALLEL PORTS 



16 BITS ADDRESSING PLUS DATA 
8 BITS AT A TIME 



DMA (IF YOU'RE CLEVER) USES 
OLD PROCESSOR MAIN MEMORY AS 
SYSTEM MEMORY EMULATED MACHINE 




YOUR OLD GENERAL PURPOSE 
PROCESSOR USED AS THE 
SYSTEM DEVELOPMENT 
PROCESSOR 



f MASS STORE k 




have to assemble yourself from high 
speed chips or run the 8X300 at less 
than its full rated speed). Assuming that 
you start with a complete computer 
system which includes assembler or high 
level language , you write the soft ware of 
a microassembler in order to create the 
emulation programs conveniently prior 
to loading the control store. You use the 
IO ports of the evaluation card (plus 
additional ones if necessary) to define 
the address and data bus structure of the 
machine you're emulating. If you're 
clever, you make this output of the 
8X300 treat your old microprocessor's 
memory as its own via the DMA trick, 
but for initial testing it is probably 
better to dedicate a small amount of 
memory (perhaps 4 K bytes) exclusively 
to the emulated machine to avoid blow- 
ups due to wild programming of unde- 
bugged machine instructions. Through 
the control and status interfaces you 
tack onto the evaluation board kit, you 
make the emulated machine treat the old 
machine and its peripherals as its main 
IO devices, so that programs working in 
the new architecture can at least talk to 
you. The result of all this cogitation and 
wiring will be a microprogrammable 
computer architecture experimental rig 
which will be the envy of many an 
industrial laboratory or university 
computer science department —yet still 
at a cost within the advanced experi- 
menter's budget.* 



100 



circuit, complete manual and assembly 
instructions. Signetics is located at 81 1 
East Arques Av, Sunnyvale CA 94086, 
and the 8X300KT100SK is available 
from Signetics distributors." 



What Makes the Z-1 Tick? 

Cromemco has forwarded this picture 
of Harry Garland's Z-80 processor card 
which is what makes their new Z-l 
computer "tick." According to 
Cromemco, they have an arrangement 
with Zilog to obtain a selected version of 
the Z-80 processor which can operate 
with a 4 MHz clock. Yet the card 
remains compatible with the Altair bus 
which is available from numerous manu- 
facturers. 

This processor card design has a 
crystal controlled 4 MHz clock which 
can drive the processor at either 4 MHz 
or 2 MHz depending upon a switch 
selected option. The use of memory wait 



states enables the board to operate with 
mixes of fast and slow memory in the 
event that an older system is being 
upgraded to the 4 MHz clock rate. 

An interesting feature which will 
prove most useful to those people who 
purchase the Cromemco Bytesaver 
EROM card (or its equivalent) in order 
to build permanent systems software 
loads is the new Cromemco Z-80 proc- 
essor card's power on restart option 
which allows selection of an automatic 
restart vector to any 4 K boundary in 
memory address space. Thus if you put 
your monitor in EROM up at hexa- 
decimal address F000, this board lets 
you set up an automatic restart jump to 
your monitor whenever you turn on the 
power (or if you're a true hacker, when 
you simulate power on with your own 
restart button). 

This processor is available either in 
kit or in assembled form at prices of 
$295 and $395 respectively. Delivery is 
quoted as 15 to 30 days ARO (after 




receipt of order). Cromemco also pro- 
vides a Z-80 monitor, with complete 
documentation including source code 
and paper tape object code. Also avail- 
able according to the press release is a 
Z-80 assembler and BASIC interpreter. 
Cromemco is located at 2432 Charleston 
Rd, Mountain View CA 94043.* 



A Matter of Form 

We recently received a pad of coding 
forms for those who work in assembly or 
machine language, designed and sold by 
Walton Electronics. The forms are bound 
together in pads of 50 sheets and are 
formatted to accept code for the more 
popular microprocessors. Columns in- 
clude: address, code, label, instruction 
and notes. Code can be written in either 
octal or hexadecimal with up to 3 bytes 
per line in regular assembler format. The 
lines are spaced to permit coding from a 
pica typewriter. 

These forms make hand assembly 
easier and neater which helps eliminate 
errors. The pads sell for $1.95 each 
postpaid. Quantity discounts are avail- 
able. Order from Walton Electronics, 
POB 503, Bethany OK 73008, or check 
your nearest computer store." 



Explore the Universe of Color 




Compucolor Corp, Norcross GA 
30071, announced plans in December 
1976 to begin marketing a new 8 color 



personal computer, the Compucolor 
8001, in early December. According 
to the press release, the Compu- 
color 8001 is a stand alone CRT and 
microcomputer with both computation 
and graphics capabilities. 

It is programmed to handle simple or 
complex tasks, from color graphics and 
income tax records to checkbook 
balancing, education instruction, tutor- 
ing and a unique variety of computer 
games. The unit features BASIC lan- 
guage, a 19 inch display screen, key- 
board and tape memory. Options are 
also available. 

The Compucolor is being marketed 
through retail computer stores nation- 
wide, and no price was quoted with the 
press release." 



INTERNATIONAL DATA SYSTEMS, INC. 



400 North Washington Street, Suite 200 
Falls Church, Virginia 22046 USA 
Telephone (703) 536-7373 



S100 Buss Cards (ALTAIR/IMSAI Compatible) 

88-SPM Clock Module 

88-UFC Frequency Counter Module 

88-MODEM Originate/Answer MODEM 

GENERAL PURPOSE PERIPHERALS 

MCTK Morse Code Trainer/Keyer 



TSM 
DAC8 



Temperature Sensing Module 



USES 

Your computer keeps time of day regardless of what program it is 
executing. Applications include event logging, data entry, ham 
radio, etc. 

Measure frequencies up to 600 MHz. Computer can monitor 
multiple frequencies such as transmit and receive frequency. 

Use your computer to call other computer systems such as large 
timesharing systems. Also allows other computer terminals to 
"dial-up" your computer. 



Hardware/ Software package which allows your computer to teach 
Morse Code, key your transmitter, and send prestored messages. 

Use it to measure inside and/or outside temperature for comput- 
erized climate control systems, etc. 



Requires one eight bit output port. Use it to produce computer 
music. 



Eight Bit Digital to Analog Converter 
Terms: Payment with order. Shipment prepaid. Delivery is stock to 30 days. Write or call for detailed product brochures. 



KIT PRICE 

$96.00 

$149.00 
$199.00 

$29.00 
$24.00 
$19.00 



101 






Technical 

Forum 



Comments on a Prototyping Bus 



(See December 1976 BYTE, page 128.) 



Webb Simmons 

1559 AlcalaPI 

San Diego CA 921 11 



This concerns the proposal for a universal 
prototyping bus structure by David 
Washburn. 

Mr Washburn raises some interesting 
points, none of which raise objections from 
me; however, when we dream let us dream 
boldly. It is not boldness to increase the 
address bus width from 16 bits to 18 bits. It 
is not boldness to replace the pseudostandard 
bus with an 88 connection bus. 

A truly bold step for the address bus is 
to immediately go to 24 bits (3 bytes). The 
processor board can have two 8 bit registers, 
loaded by 10 instructions (but it does not 
matter how they get loaded), to supply the 
upper 8 bits of an address. The choice of 
which upper register to use would be based 
upon whether it is an instruction fetch. [Not 
necessarily possible to determine with any 
processor chip . . . CH/ In this way instruc- 



tions and data can be arbitrarily far apart. 
The actual loading of the upper address 
register should be deferred by one instruc- 
tion time to allow for a jump into the newly 
selected memory block. Many variations on 
this theme are possible and none would be 
binding upon any user. Merely allow 24 bits 
and let each person do his/her own thing. 

Similar reasoning suggests 24 bits for the 
data bus. [But why not go all the way to 
32 ? ? ? CH/ A person with true 16 bits of 
data may wish to use a Hamming code for 
error correction as well as (in lieu of) simple 
error detection. A 21 bit field is required to 
correct a one bit error in 16 bits (see the 
Data General description of their Eclipse 
computer). Once again a person may either 
use the extra bits or ignore them. 

I rather like the thought of multiple 
inexpensive connectors, butwhystopattwo? 



Some Comments on the Universal Bus Idea 



M Faiman 

Associate Professor of Computer Science 

University of Illinois at Urbana-Champaign 

Urbana IL 61801 



David Washburn's comments in the 
December issue of BYTE on a universal bus 
structure are well taken. We ran into the 
problem he describes a couple of years ago 
when we started to experiment with micro- 
processors in our department. Every micro- 
processor, as your readers well know, has its 
own external signal configuration and proto- 
col which all other devices — memory boards, 
10 interfaces, etc, must match in order to 
form a working system. Changing processors, 
even if they cost a mere $25, necessitates a 
costly redesign of all the associated device 
interfaces. Since there are typically many of 
the latter for only one of the former, this is 



obviously an expensive and, in most 
instances, impractical business. 

Our solution, after studying the charac- 
teristics of the popularly available and 
projected microprocessors, was to design our 
own Modular Unified Microprocessor 
System - MUMS (1, 2, 3, 4). This system 
has undergone two design iterations since its 
inception, and its chief characteristics may 
be summarized as follows: 

1. The hardware utilizes a fairly simple, 
uniform bus structure that is processor 
independent. There is one micro- 
processor per bus, and it and all other 
devices intercommunicate via a small 
set of generic signals (see item 5 
below). 

2. The bus signal protocol is chosen so 
that the most numerous modules in a 
system require only the simplest, ie: 
least expensive, interfaces. 



102 






Use three connectors or even four. When a 
user has no need for the extra connectors 
they can be omitted from the mother board. 
The standard board size might increase 
somewhat but the extra square inches will 
not be very expensive. 

The 3 bit "speed code" set by each mem- 
ory board seems to have no advantage over a 
one bit "data ready" signal from memory. 
Unless and until the data is truly ready the 
processor can do nothing sensible anyway. 
Many computers already allow for asyn- 
chronous memory with an indefinite wait 
for data ready, so this in not new. 

Concerning standard peripheral device 
numbers, why not define them in the range 
from a low of zero to a high of 255? Then 
allow anyone to append one or two upper 
bytes to this low byte of standard assign- 
ments. The upper byte (or bytes) could be 
set with jumpers or dip switches. This will 
allow the spirit of standard device assign- 
ments and still let a user put them where he 
wishes. 

For multiple processors (eg: 2) let us not 
overlook the possibility of Y shaped mem- 
ory in which each processor gets its instruc- 
tions from its own branch of the Y without 
conflicts with the other processor. For data 
the processors can share the common branch 
and most of the time both processors can 
run at near full speed." 



To sidestep the spread in timing 
requirements of different processors 
the mode of communication on the bus 
is asynchronous. A particular advan- 
tage of this is that memory boards of 
differing access/cycle times can be 
used in the same system. (There is no 
need for the "speed code" number 
that Mr Washburn describes.) 
Multiprocessing is accomplished with 
the aid of a TIE module and, option- 
ally, a COM-UNIT. The former plugs 
into any MUMS bus and appears to the 
processor as a DMA device. From its 
other end a 4 wire line (10 MHz serial) 
can talk to a similar module on 
another bus for dual processor activity, 
or to the COM-UNIT - in process of 
design right now — which will handle 
communication between up to 16 
processors. 

The bus is physically implemented on 
a 72 pin connector (DEC compatible), 
as shown in the figure. Of these, the 
DATA, ADDRESS and POWER lines 
are self-explanatory. The others have 
mnemonic names, as follows: 



r 




16 K STATIC RAM 

For ALTAIR / IMSAI / POLY 88 

$459 kit 

ASSEMBLED$529 



• USES 4K STATIC RAMS -NO REFRESH 

• VERY LOW POWER -LESS THAN 1 AMP 

• Z80 FAST - 200ns ACCESS TIME 

• PROVISION FOR BATTERY BACKUP 

• LOW PROFILE SOCKETS FOR ALL CHIPS 

• EACH 4K ADDRESSABLE TO ANY 4K SLOT 

• HARDWARE/SOFTWARE MEMORY PROTECT 
FOR EACH 4K 

• SPECIAL PAGING OPTION ALLOWS UP TO 
1 MEGABYTE ADDRESSABLE MEMORY 

• LOW COST 

CONSTRUCTION MANUAL $1 .75 

PAGING OPTION $9.00 

QUANTITY DISCOUNT 5 BOARDS — 5% 

10 OR MORE— 10% 
DEALER INQUIRIES INVITED 

OMNI SYSTEMS INC. 

P.O. BOX 7536, UNIV. STATION 
PROVO, UTAH 84602 

READER SERVICE NO. 198 




Featuring the 

test equipment 

and accessories 

you've been 

looking for in 

money-saving, 

easy-to-build 

kit form. 



And our new catalog also lists hi-fi, television, amateur 
radio products and much more . . . nearly 400 quality elec- 
tronic kits for your every interest. You'll find Heathkit 
building easy and enjoyable with our famous step-by-step 
assembly manuals. And we won't let you fail. Should you 
have the slightest problem, an experienced staff of tech- 
nical advisors awaits your phone call. 
Send for your FREE catalog today. You'll see why quality 
reliability and serviceability are familiar words to a 
Heathkit customer. 
Heath Company, Dept. 334-27, Benton Harbor, Michigan 49022 




I 
I 



Heath Company, Dept. 334-27 
Benton Harbor, Michigan 49022 

Please send my FREE Heathkit catalog. I am not on your maHing list. 



Name_ 



Address_ 



City_ 



_State_ 



I 
I 



CL-627 



ZiP- 



103 












Expansion 



Component 
Side of Card 



BD15 

BD14 

BD13 

BD12 

BD11 

BD10 

BD9 

BD8 



BA15 

BA14 

BA13 

BA12 

BA11 

BA10 

BA9 

BA8 



GND 
GND 
+ 5 
+ 12 
-12 

RST 

RAV 

WHD 

DGI 

I/O 

ISN 

IGI 

IA3 

IA2 

IA1 



1A 
1B 
1C 
1D 
1E 
1F 
1H 
U 
1K 
1L 
1M 
1N 
1P 
1R 
1S 
1T 
1U 
1V 



- 3A 

- 3B 

- 3C 

- 3D 

- 3E 
x 3F 

- 3H 
x 3J 

- 3K 
x 3L 

- 3M 

- 3N 

- 3P 

- 3R 

- 3S 

- 3T 

- 3U 

- 3V 



2A 
2B 
2C 
2D 
2E 
2F 
2H 
2J 
2K 
2L 
2M 
2N 
2P 
2R 
2S 
2T 
2U 
2V 



4C 
4D 
4E 
4F 
4H 
4J 
4K 
4L 
4M 
4N 
4P 



BD7 
BD6 
BD5 
BD4 
BD3 
BD2 
BD1 
BDO 



BA7 
BA6 
BA5 
BA4 
BA3 
BA2 
BA1 
BAO 



4A - GND 
4B - GND 



+ 5 
+ 12 
-12 

a£R 

WAV 



- WAV / 

x 

- WLD ) 



WLD 
DGO 
DMR 
4R - IVV 
4S - IGO 
FES 
TR2 



4T 
4U 



4V - IRI 



DATA 



MEMORY 



DMA 



INTERRUPT 



MUMS Bus - Signal Layout 



DMR - DMA device Request 

DGI/DGO - DMA Grant In/Out 

(daisy chained signal) 
IO — Used in conjunction 

with appropriate mem- 
ory control signals to 
access an IO page. 

- Interrupt Sync (proc- 
essor generated) 

- Interrupt Request for 
level i (i = 1,2,3) 

- Interrupt Acknowledge 
for level i 

- Interrupt Grant In/Out 
(daisy chained signal) 

- Interrupt Vector Valid 
(device to processor) 

It is obviously beyond the scope of this 
letter to describe timing relationships in 
detail, but the interested reader may find 
control particulars in references 2 and 4 below. ■ 

REFERENCES 

1. Faiman, M : Modular, Unified Microprocessor 
System (MUMS), ACM Computer Science 
Conference Abstracts, page 19, February 1976. 







ISN 


ADDRESS 


Foil Side 


IRi 
lAi 




of Card 


IGI/IGO 


POWER 




lW 



RST 


— Power on reset 


RAV 


- Read Address Valid 




(from processor DMA 
device to memory or IO 


WAV 


device register) 
- Write Address Valid 


ACK 


(similarly) 
— Acknowledge (opposite 
direction) 


WLD 
WHD 


— Write Low Data byte 

- Write High Data byte 



2. Catlin,R W: MUMS: A Modular, Unified Micro- 
processor System, (50 pages, Technical Report 
UIUCDCS-R-76-809, University of Illinois, 
Urbana-Champaign), IEEE Computer Society 
Repository #R76-245. 

3. Faiman, M, Catlin, R W and Weaver, A C: 
A Modular, Unified Microprocessor System 
(MUMS), Proceedings of the IEEE DISE Work- 
shop on Microprocessors, pages 1-5, Colorado 
State University, August 1976. 

4. Faiman, M, Weaver, A C and Catlin, R W: 
MUMS — A Reconfigurable Microprocessor 
Architecture, Computer, January 1977. 



What's 



Computer Power & Light 

Gene Morrow, president of Computer 
Power & Light, a computer store located 
at I 232 1 Ventura Blvd, Studio City CA 
91604, has sent along a brochure des- 
cribing his firm's packaged 8080 proc- 
essor system. The Computer Power & 
Light COMPAL-80 computer is a fully 
assembled system for homes and small 



businesses, which includes the following 
main features: 

• 8080A processor 

• audio tape serial interface port 

• Teletype or RS-232 serial port 

• 1 2 K programmable memory 

• 16 line by 64 character video 
display with full ASCII character 
set and graphics 

• 9 inch high resolution monitor 

• ASCII keyboard with capacitance 
switch mechanisms 

• case and cabinetry with cooling 
phan, chassis connectors for 
interfaces, "turn key" con- 
figuration 

• PROM monitor to eliminate the 
need of a costly front panel 

• 10 K extended BASIC including 
formatted PRINT, double preci- 
sion, all transcendental functions, 
etc. 

The price on the above package of 
features is quite reasonable — for $1 863 



you get a completely assembled system 
which can be viewed and examined in 
Gene's store. Gene's press release claims 
that several systems already have been 
delivered including one which is in use at 
Mt St Mary's College in Los Angeles as 
part of a computer programming cur- 
riculum, another which is being used to 
keep track of inventory in a retail store 
in Santa Barbara, and another in an 
industrial laboratory. For more informa- 
tion, contact Gene at the store." 



A New Version of SC/MP 

National Semiconductor has now 
introduced a new version of the SC/MP 
processor (see Robert Baker's article in 
September 1976 BYTE, page 76). This 
newer version is implemented with a 
faster NMOS technology with the 
following essential points of improve- 
ment: 



104 



• Twice as fast in execution (3.58 
or 4.0 MHz on chip crystal) 

• One quarter of the power require- 
ments (200 mW versus 800 mW) 

• Compatibility with the previous 
product 

• Single power supply 

According to the press release, this 
new version is being sampled from the 
factory at $17.76 for single quantities 
and in 1 977 the production quantities of 
1000 or more will sell "significantly 
below $10 each" when it becomes avail- 
able in a plastic package. National Semi- 
conductor also plans to have available a 
retrofit kit for present owners of SC/MP 
kits, which will allow conversion to the 
new processor. The price for this prod- 
uct is not yet announced. 

This is the kind of processor which 
rapidly becomes a commodity part, and 



can thus be buried into all manner of 
dedicated application products with ap- 
propriate read only memory software 
designs and special purpose peripheral 
hardware. For an example of such dedi- 
cated products, consider the dedicated 
electronic music synthesizer module: 
Hypothesizing a $2 to $5 price for a 
plastic package version of this computer, 
using perhaps 1 or 2 K of 2708 storage 
for control programs, and perhaps 1 K or 
so of programmable memory for param- 
eters, it should be possible to engineer an 
inexpensive stand-alone music synthe- 
sizer module which will sit on a com- 
puter table and take orders through a 
high speed serial port and RS-232 level 
receivers. 

National Semiconductor is located at 
2900 Semiconductor Dr Santa Clara CA 
95051. National Semiconductor parts 
and products are available through most 
nationwide electronic distributors." 




Floppy Disk Controller 

And a Hint about a Future Article 

NEC Microcomputers Inc, Five Mi- 
litia Dr, Lexington MA 02173, has a 
pair of the most advanced LSI devices 
available for peripheral control in micro- 
processor systems. This pair consists of 
the uPD372D floppy disk controller chip 
(now available at $54 in quantities of 1 
to 24) and the UPD371D cassette con- 
troller chip (also available, in quantities 
of 1 to 24 quoted at $48). Both these 
items are available from a nationwide 
network of distributors, which in New 
England includes Harvey Electronics, 
Semiconductor Specialists and Sterling 
Electronics. Tim Schoechle, of the Tech- 
nical Staff for Microprocessors of NEC, 
sent along the latest technical manual on 



the floppy disk controller chip, for use 
as a reference in editing a forthcoming 
article by Ira Rampil which reviews both 
of these controllers. 

When you buy one of these chips, 
you get a fixed purpose processor which 
is customized to the job at hand. As 
described in the 68 page uPD372D disk 
controller manual (dated December 3 
1 976, which we understand was written 
by Tim), the chip takes care of all the 
housekeeping and formatting require- 
ments at the hardware level needed to 
create floppy disk records with 
IBM 3740 format, Shugart Minifloppy 
format, etc. It also generates and checks 
cyclic redundancy characters, can be 
synchronized with address marks or 
physical indices (so called "hard sec- 



tors"), and will handle up to four floppy 
disk drives through separate select lines. 
Furthermore, it has the capacity to 
overlap input and output control of two 
separate drives. Taking into account dif- 
ferences in hardware, the track to track 
stepping rate and stepping pulse width 
outputs are programmable, as is the 
sector size and data rate. A list of 
13 drives with which the chip is com- 
patible is given by manufacturer and 
model number. More detailed informa- 
tion will have to wait for Ira's arti- 
cle — but for the engineers or home- 
brewers who can't wait, the information 
is available from NEC or its repre- 
sentatives: Ask for the "uPD372D LSI 
Floppy Disk Controller Chip User's 
Manual."" 



MVM 1024 Microprocessor Video 

Module 



lllllllllllllTHlil 




^ Sixteen 64-character lines, upper /lower case 128 character font. 

^ Software-controllable reverse video characters. 

^ Full read and write capability for both cursor position and character code. 

^ Interfaces to any microprocessor: 8080, 6800, 6502, etc. 

^ Scrolling, line/character insert/delete, etc. easily done with software. 

THE SOPHISTICATED VIDEO MODULE 
$225 FOR THE ADVANCED EXPERIMENTER 



ASSEMBLED 
AND TESTED 



J±«£ 



Write or call for complete literature. 

Riwrside 



ELECTRONIC DESIGN INC. 



1700 NIAGARA STREET 

BUFFALO, N.Y. 14207 

716 875-7070 



105 






Flights of Fancy 
with the Enterprise 



David Price 
3901 Victoria Ln 
Midlothian VA 231 13 



Listing I : The Star Trek program, expressed in BASIC. For notes on con- 
version to A/tair BASIC see the text. This version requires 9382 bytes of 
work space for the program text, 161 matrix elements, and 46 bytes of 
character string space. The approximate total size requirement is thus 10 K 
bytes, plus the size of the BASIC interpreter itself. Using a 12 K extended 
BASIC interpreter, this program would thus require approximately 22 K of 
programmable memory in a typical microcomputer system. Hurrah for the 
16 K chips! 



10 
20 
3D 
40 
50 
60 
70 
60 
90 
10 
110 
120 
130 
140 
15 
160 
17 
BO 
90 
200 
210 
SO 
230 
240 
250 
260 
270 
30 
290 
300 
310 
320 
330 
340 
350 
350 
370 
310 
390 
4)0 
410 
420 
430 
440 
450 
450 
470 
410 
490 
500 
510 
SO 
530 
540 
550 
560 
570 
SO 

so 

600 
610 
620 
630 
640 
650 
660 
67 



STAR TREit 



STTR: SPACE WAR SIMULATION 



PROGR/W BY DAVID PRICE 



REM * 
REM « 
REM * 
REM * 
REM * 
REM ......................................... 

DEF FNACX> = INTCX*RNDC 1>+ 1) 
DIM G[8,8]/Z$C 153, CSC6],X*C 24J 
T0 = T=CFNAC20> + 20)*100 
E=>30 
P= 15 
S=0 

X$=- 

DEF FNDCDXSQRCCKfl, IJ-Sf) 2 + CKC I , 2) -S2> " 2) 

Q1=Q2=S1 = S2*FNAC8> 

MAT C=CONC9,2] 

CC2, 1] = CC3^ 1XCC4, 1J = CC4, 2] = CC5,2J = CC6j2] = - 1 

CC 1* l]aCC3/2] = CC5^ n = CC7,2XCC9, 13 = 

MAT D=ZERC6] 

B9=K9=0 

FOR I" 1 TO 8 

FOR J=l TO 8 

K3=B3=0 

IF RND< IX. 8 THEN 270 

K3 = FNA<3) 

K9»K9+K3 

IF RND( IX. 9 6 THEN 30 

B3=I 

B9=B9+ I 

S3=FNA<5> 

GCI,JJ*K3*100+E3*10+S3 

NEXT J 

NEXT I 

IF K9=0 OR B9=0 THEN 200 

GOTO 3570 

IF 01 >» 1 THEN 38 

S1-Q1=1 

IF Ql <= 8 THEN 400 

S1=Q1»8 

IF Q2 >» 1 THEN 42 

S2»Q2»1 

IF 02 <= 8 THEN 440 

S2=Q2=8 

X = G[Ql, Q2D/1 00 

K3»INT(X> 

B3=INTC(X-K3>*10> 

S3-GCQ1, QZ]-((B3*10> + (K3*10 0>> 

IF K3=0 THEN 52 

PRINT "COMBAT AREA", "CONDITION RED" 

IF S>(K3* 100) THEN 52 

PRINT " SHIELDS DANGEROUSLY LOW" 

MAT K»ZERC3, 31 

MAT Q=ZERCB,8D 

QCS1,S23»1 

FOR 1-1 TO K3 

GOSUB 3500 

QCR1,R23 = 2 

KCI, 13 = R1 

KCI,23 = R2 

KC X* 3J-200 

NEXT I 

IF B3=0 THEN 650 

GOSUB 35 

QCRI,R2J = 4 

FOR 1=1 TO S3 

GOSUB 35 

QCR1,R23 = 3 



The main objective of this version of the 
Star Trek game is to destroy all of the 
Klingon battle cruisers within 30 stardates. 
The Klingons and starbases are randomly 
positioned within a simulated galaxy. To 
help you better visualize this galaxy we use 
quadrant sector notation. 

The galaxy is divided into a matrix of 8 
by 8, or 64, quadrants. Each quadrant is 
further subdivided into an array of 8 by 8 
sectors. The United Space Ship Enterprise, 
of which you are captain, has been assigned 
to seek out and destroy all of the Klingon 
invaders. You have at your disposal a bris- 
tling array of sophisticated weaponry includ- 
ing phasers, photon torpedoes, and an 
onboard computer, which are triggered by 




Once upon a time there was Star Trek. 
During its brief but eventful life as a 
television series it not only won acclaim 
from within the science fiction community, 
but was also hailed by the popular media as 
one of the first truly intelligent shows on 
television. It attracted an entirely new type 
of audience to science fiction including 
many from the computer crowd. By showing 
us glimpses of a distant future, it allowed us 
to take a more objective look at the present 
Star Trek now survives only in rerun form 
and in the games of computer people. Those 
computer people who happen to be Trekkies 
have adopted the Star Trek theme as their 
own. Everybody under the sun has been 
programming games based loosely on Star 
Trek. These games have evolved into some of 
the most complex computer games ever 
written. Yet, lurking beneath this com- 
plexity lies a startling amount of realism. 







106 



your direct orders. To utilize the facilities of 
the Enterprise you enter simple numerical 
commands. Figure 1 shows the flowchart for 
^'he initialization of the variables used in the 
program and the first quadrant set up. The 
flowchart also indicates on what lines of the 
program the various operations take place. 

The Command Set 

Figure 2 shows the flowchart for entering 
commands to the program. The commands 
are numbers which are tested by the pro- 
gram to determine what to do. 

Command places you in control of the 
warp engines which are used to propel the 
Enterprise from one location to another. 
You are first asked for the direction in 
which you wish to travel. The trajectory 
angles are arranged on a circular vector as 
shown in figure 3. 



Listing 1, continued: 



f START j 



90 



INITIALIZE 
VARIABLES 



210 



INITIALIZE 

GALAXY 

ARRAY 



3570 




3610 



OUTPUT 
INSTRUCTIONS 



440 



INITIALIZE 
QUADRANT 




390 



440 



MOVE TO 

LEGAL 

QUADRANT 



INITIALIZE 
QUADRANT 
ARRAY 



2600 



OUTPUT 
SHORT RANGE 
SCAN 



(COMMAND ) 



Figure 1: Flowchart for 
the initialization of the 
Star Trek program. The 
numbers in the flowcharts 
of this article refer to 
line numbers in the pro- 
gram found in listing 1. 
Once initialization is com- 
pleted, execution flows to 
the command interpreter. 



so 

690 
70 
710 
720 
730 
74 
750 
760 
770 
750 
790 
80 
810 
820 
830 
840 
850 
860 
870 
8B0 
890 
90 
910 
920 
930 
940 
950 
960 
970 
936 
990 
10 

10 10 
102 
1030 
1040 
1050 
1060 
1070 

108 

109 

110 

11 10 
1120 
1130 
1140 
1150 
1160 
1170 

118 

119 
1200 
1210 
1220 
2230 
1240 
1250 
1260 
1270 

128 

129 
D00 
D10 
132 
1330 
134 
1350 
1360 
1370 

138 

139 
1400 
1410 
1420 
1430 
1440 
1450 
1460 
W7 

148 

149 
1500 
1510 
1520 
1530 
1540 
155 
1560 
1570 
1580 
159 
1600 
JS1Q 
1620 
1630 
1640 
1650 
1660 
167 
*8Q 
169 
17 
17 10 
1720 
1730 
1740 
17 5 
1760 
1770 
178 



NEXT I 

GOSUB 2600 

PRINT "COMMANDi "; 

INPUT A 

IF A< 1 OR A>5 OR A#INTCA) THEN 780 

R1=A+ 1 

IF DCR1] >= THEN 780 

GOSUB 3420 

PRINT Z$;" NOT OPERATIONAL" 

GOTO 700 

GOTO CA+1) OF 890,1520,1640-1800*2200.3010*3550 

PRINT 

PRINT "0=SET COURSE";TAB<2 0>;"4 3 2" 

PRINT -l=LONG RANGE SCAN"; TAB< 2 1) ; "\ * /" 
"2 = PHAS£R CTRL";TABC22)J"W" 

•3=TORPEDO CTRL-;TAB( 18);"5 1" 

"4=SHIELDS";TAB(22)J "/~\" 

"5= LIBRARY COMPUTER"; TABC 2 1) ; "/ " \" 

"6=RESIGNATION";TA8C2 0);"6 7 8" 



PRINT 

PRINT 

PRINT 

PRINT 

PRINT 

PRINT 

GOTO 70 

PRINT "COURSE C 1-9):"; 

INPUT CI 

IF C1<1 OR CI >= 9 THEN 7 00 

PRINT "WARP FACTOR (0-8):"; 

INPUT VI 

IF Wl <= OR Ul>8 THEN 700 

IF DC I] >= OR VI <= .5 THEN 98 

PRINT "ENGINES ARE DAMAGED, MAXIMUM SPEED* WARP . 5" 

GOTO 920 

IF E-(V1*8)>0 THEN 1030 

IF S< 1 THEN 247 

PRINT "YOU ONLY HAVE"; E; "UNI TS SUGGEST YOU CROSS- W RCUI T" 

PRINT "FROM SHIELDS, WHICH HAVEN'S; "UN I TS" 

GOTO 700 

FOR 1=1 TO 6 

IF DC I ] >=» THEN 1060 

DCI]»DCI]+1 

NEXT I 

IF FNA(10)#5 Cm VK2 THEN 1120 

Rl = FNA(6) 

DCRI] = DCR1]-FNA(5> 

GOSUB 342 

PRINT LINC 1), "DAMAGE CTRL REPORTS *",*2$;" DAMAGED. '",LIN( 1) 

N=INTCW1*8) 

QCS1, S21*0 

X=Sl 

Y = S2 

C2=INT(C1) 

X1 = CCC2, 13 + CCCC2+ 1, IJ-CCC2, |])*CC1-C2> 

X2 = CCC2, 2J+CCCC2+ 1, 23-CCC2, 23)*(C1-C2) 

FOR 1*1 TON 

S1 = S1 + X1 

S2*S2+X2 

IF SKI OR Sl>8 OR S2< 1 OR S2>8 THEN 1360 

IF QCINT(S1),INT(S2)3 = THEN 1270 

S1 = S1-XI 

S2» S2-X2 

GOTO 128 

NEXT I 

SlalNT(Sl) 

S2=INTCS2> 

Q[S1,S23 = 1 

E=E-N 

IF VK1 THEN -69 

T=T+l 

IF T>T0+30 THEN 250fl 

GOTO 69 

X = Q1*8 + X+X1*N 

Y=Q2*8+Y+X2«N 

Ql=INTCX/8) 

Q2=INTCY/8) 

Sl = INT(X-Ql*8+.5) 

S2»INTCY-Q2*8+.5) 

IF S1>0 THEN 1450 

Q1 = Q1-1 

Sl = 8 

IF S2>0 THEN 148 

Q2=Q2-1 

S2=8 

T=T+ 1 

E=E-N+5 

IF T>T0+30 THEN 2500 

GOTO 360 

PRINT XSC 1, 17] 

FOR I«Q1-1 TO Q1+ 1 

MAT N=£ERC33 

FOR J*Q2-1 TO Q2+ 1 

IF Kl OR I>8 OR J<1 OR J>8 THEN 158 

NCJ-Q2+2]=GCI,J] 

NEXT J 

PRINT USING 1630;NC 13,NC23,NC 3] 

PRINT XSC 1, 17] 

NEXT I 

GOTO 700 

IMAGE "i ",3<3D," 1 ") 

IF K3=0 THEN 2350 

PRINT "ENERGY AVAILABLE* "; E 

PRINT "NUMBER OF UNITS TO FIRE:"; 

INPUT X 

I F X< 1 THEN 7 

IF E-X<0 THEN 166 

E=E-X 

FOR 1= 1 TO 3 

IF KCI,3]*0 THEN 178 

H = INTCX/K3/CFNDC 0) ) > 

KCI,3]=>KCI, 3]-H 

PRINT h;-unit HIT ON KLINGON" 

IF KCI,3J>0 THEN 178 

GOSUB 2 050 

NEXT I 



107 









Listing 1, continued: 



179 GOTO 20 3 

BOO IF P>0 THEN 1830 

BIO PRINT "ALL PHOTON TORPEDOES EXPENDED" 

B20 GOTO 700 

B30 PRINT "TORPEDO COURSE (1-9):"; 

B40 INPUT CI 

B50 IF CK1 OR CI >= 9 THEN 700 

B60 C2 = INTCC1> 

B70 X1 = CCC2, 13+CCCC2+ U 13-CCC2. |])«(C1-C2) 

B8 X2=C[C2,23+<CCC2+1..23-CEC2 J 23)*CC1-C2) 

B90 X=S1 

POO Y= S2 

P 1 P=P- 1 

1920 PRINT 

19 3 X=X+X1 

19 4 Y=Y+X2 

P50 IF X<1 OR X>g OR Y<1 OR Y>8 THEN 218 8 

P60 IF QCINTCX),INTCY)3=0 AND QC INTCX+ . 5) * INTO Y+ . 5) 3 = THEN 1930 

070 FOR 1 = 1 TO 3 

P80 IF INT(X) 3 KtLI] AND I NT(Y) = KC I j 23 THEN 2020 

1990 IF INT<X+.5) = KCI, ID AND INTCY+ . 5) »KC I j 23 THEN 2020 

2000 NEXT I 

20 10 GOTO 2120 
2020 GOSUB 2050 
20 3 GOSUB 2370 
2040 GOTO 700 

2050 KCI,33=QCKCI, 1 ],KEI# 233 = 

20 6 PRINT "***KLINGON DESTROYED*** " 
2070 K3=K3-1 

208 K9=K9- 1 

209 I F K9= THEN 2550 
2100 GCQ1, Q23 = G[QUQ23- 100 

21 1 RETURN 

2120 IF QCINT(X)>INT(Y)3#3 THEN 2150 

2130 PRINT "YOU CAN'T DESTROY STARS* SILLY!" 

2140 GOTO 2180 

2150 PRINT "***STARBASE DESTROYED***" 

2160 PRINT "YOU ARE HEREBY RELIEVED OF DUTY I I CONGRATULATIONS ! " 

217 GOTO 2 53 

218 PRINT "TORPEDO MISSED" 

219 GOTO 2030 

200 PRINT "ENERGY AVAILABLE="; E + S 

2210 PRINT "NUMBER OF UNITS TO SHlELDSi"; 

2220 INPUT X 

2230 IF X<0 THEN 700 

2240 IF E+S-X<0 THEN 2210 

2250 E=E+S-X 

226 S=X 

2270 GOTO 700 

8280 PRINT LIN< 1 ) ; "DEVI CE"; "STATE OF REPAIR" 

229 FOR Rl=l TO 6 

2300 GOSUB 3420 

2310 PRINT Zi> DCR13 

2320 NEXT Rl 

2330 PRINT 

2340 GOTO 700 

2350 PRINT "SHORT RANGE SENSORS REPORT NO KLINGONS IN THIS QUADRANT" 

2360 GOTO 700 

2370 IF Cl="DOCKED" THEN 2460 

2380 IF K3=0 THEN 2460 

2390 FOR 1=1 TO 3 

2400 IFKCI..33-0 THEN 2450 

2410 H = INT(KCI*33/FNDC 0)+ 1) 

2420 S = S-H 

2430 PRINT HJ-UNIT HIT ON ENTERPRISE" 

2440 IF S<0 THEN 2520 

2450 NEXT I 

2460 RETURN 

2470 PRINT "**FATAL ERROR** " 

2480 PRINT "THE ENTERPRISE IS DEAD IN SPACE* AND MUST BE EVACUATED ! 1 " 

249 GOTO 2530 

2500 PRINT LINC 1)* "IT IS STARDATE"; T 

2510 GOTO 2 53 

2520 PRINT LINCIJ;" ***THE ENTERPRISE HAS BEEN DESTROYED***" 

2530 PRINT LIN(1)*-THE FEDERATION WILL BE CONQUERED I ! I " 

2540 SOTO 3560 

2550 PRINT 

2560 PRINT "THE LAST KLINGON BATTLE CRUISER HAS BEEN DESTROYED!!" 

2570 PRINT "THE FEDERATION HAS BEEN SAVED I!" 

258 PRINT 

259 GOTO 3560 

26 FOR I = S1- 1 TO S 1+ 1 
25 10 FOR J=S2- 1 TO S2+ 1 

2520 IF l<\ OR I>8 OR J< 1 OR J>8 THEN 2640 

2630 IF QCI*J3 = 4 THEN 2670 

2540 NEXT J 

2650 NEXT I 

2660 GOTO 2730 

2670 CI="DOCKED" 

268 E= 3 

269 P=15 

27 MAT D=2ER 
27 1 S= 

27 2 GOTO 28 1 

273 PRINT 

2740 IF K3>0 THEN 278 

2750 IF E<300 THEN 28 

2760 CS="GREEN" 

27 7 GOTO 28 10 

2780 C$="*RED*" 

279 GOTO 28 1 

23 00 CS= "YELLOW" 

310 PRINT X$ 

320 2=0 

2330 GOSUB 3330 

SB40 PRINT 

250 GOSUB 332U 

S860 PRINT "STARDATE"; SPAC 5); T 

370 GOSUB 3330 

238 PRINT "CONDITION"; SPA( 5); C$ 

2390 GOSUB 3330 

2900 PRINT "ENERGY*"; SPA< 7 ) ; E 



Figure 2: Command inter- 
preter. A very simple inter- 
preter is employed by the . 
program. It requests a 
command input, tests the 
command for validity with 
a computed GO TO at line 
780 to activate the appro- 
priate command segment. 
Invalid commands fall 
through the GO TO state- 
ment and lead to printing 
of a command list on the 
output display. 



f COMMAND J 








^L_ 




700 




NO 


800 


* 


INPUT 
COMMAND 






780 J\^ 

v^valid\. 


OUTPUT 

COMMAND 

LISTING 




NO 






YES 


760 


^^DEVICE^^ 


INFORM 
USER 








780 


YES 






/appropriate^ 

I COMMAND j 





One warp factor represents the length of 
one quadrant. It is possible to move very 
short distances by using warp factor values 
less than one. Every time you move to a new 
location, you will get what is known as a 
short range scan which is a printout of the 
quadrant you are currently in. The symbols 
used in the short range scan are: 

Enterprise <*> 

star * 

Klingon +++ 

starbase>!< 
Figure 4 shows the actions which take place 
during the execution of this command. 

Occasionally, after using enough warp 
factors to get you to who knows where, you 
will discover that you haven't gotten any- 
where. This is because you have run into 
something, probably a star. Fortunately,^^ 
your warp engines will always bring you to a 
screeching halt in time to prevent an acci- 
dent. This is why it is a good idea to check 
your short range scan before laying out a 



108 



Figure 3: Course vector diagram. Numbers 
are used to determine the direction in which 
the Enterprise will move } or a photon 
torpedo is fired. These numbers are related 
to the points of a compass as shown here; 
fractional values are used to generate points 
in between these major headings. 



Listing I, continued: 




course, to make sure you have a clear path 
to your destination. 

Command 1 will output a long range 
scan. A long range scan is a table containing 
information on the quadrants bordering the 
one you are in. It is arranged on a 3 by 3 
grid, with your own quadrant being the one 
in the center. You are given a three digit 
number for each quadrant. The hundreds 
digit of this number is the number of 
Klingon ships in that quadrant. The tens 
digit is the number of starbases, and the ones 
digit is the number of stars. Be sure to 
remember that leading zeroes will be sup- 
pressed on the printout. Sometimes an entire 
row on the long range scan will be made up 
of zeroes. This represents the edge of the 
galaxy, the perimeter of your range. The 
warp engines will not permit you to enter 
this area. Instead, you will bounce off the 
edge. 

Command 2 is the phaser firing section. 
You may destroy a Klingon ship by firing 
enough units of phaser power to deplete his 
shields. The question is, how many units are 
necessary to do this? One factor you must 
consider is the amount of energy he has in 
his deflector shields. For every unit of 
energy you hit him with, his shields drop a 
corresponding amount. Your distance from 
the Klingon also matters since the amount of 
energy that reaches him lessens with dis- 
tance. Your sensors will tell you how suc- 
cessful you have been in damaging the 
Klingons. Your phaser fire is evenly divided 



£10 
392 
330 
2540 
2550 
2560 
2570 
980 
259 
3000 
3910 
3020 
3030 
30^0 
3950 
3060 
3070 

308 

309 

310 
3110 

312 

313 

31 4 
3150 

316 

317 

318 

319 
3200 
3210 

3220 
323 
3240 
3250 
3260 
3270 

328 

329 
3300 
3310 
3320 
333 
3340 
3350 
3360 
3370 

338 

339 
3400 
341Q 
342 
3430 
3^4 
3450 
3460 

347 

348 

349 
3500 
3510 
3520 
3530 
3540 
3550 

356 

357 

358 

359 
3600 
3610 
3520 
3530 
3640 
3650 
3560 
3670 



GOSUB 33 30 

PRINT "TORPEDOES"; SPA< 4) ;P 
GOSUB 3330 

PRINT "SHIELDS"; SPA( 6); S 
GOSUB 3330 

PRINT "KLINGONS"; SPAC 5) ;K9 
GOSUB 333 
PRINT 
PRINT XJ 
RETURN 

PRINT "COMPUTER ACTIVE AND AWAITING COMMAND"; 
INPUT A 

GOTO CA+1) OF 228 0' 31 00, 331 
PRINT "FUNCTIONS AVAILABLE FROM COMPUTER" 
PRINT " 0»DAMAGE REPORT" 

PRINT " 1= PHOTON TORPEDO DATA- 

PRINT " 2=SHORT RANGE SCAN- 

PRINT 
GOTO 30 10 
PRINT 

FOR 1=1 TO 3 

IF KCI,33 <= THEN 3200 
X=KCI,2]-S2 
Y=S!-Kt I, n 
IF X = THEN 3240 

A=INTCCC57.3*ATNCY/X))/45+ D* 10 0)/ 100 
IF X>0 AND Y<0 THEN 329 
IF X<0 THEN 3220 
PRINT "DIRECTION*"; A 
NEXT I 
GOTO 700 
A=A+4 
GOTO 3 19 
IF Y<0 THEN 327 
A=3 

GOTO 3190 
A=7 

GOTO 3 19 
A=A+8 
GOTO 3 19 
GOSUB 2600 
GOTO 700 

REM ♦#*#♦ OUTPUT QUADRANT ***** 
Z = Z+ 1 

FOR 1=1 TO 8 
£$=" <*>+++ * >!<" 
PRINT ZSCGCZ,I3*3+ 1j QC Z» 13*3+3 3; 
NEXT'I 

IF Z=l OR 2=8 THEN 3410 
PRINT SPAC5); 
RETURN 

REM ***** PRINTS DEVICE NAME ***** 

RESTORE 3440 „_ , ,_„„ 

DATA "WARP ENGINES", "SCANNERS", "PHASER BANKS", "TORPEDO TUBES- 
DATA "SHIELD CTRL", "COMPUTER" 
FOR X=l TO Rl 
READ ZS 
NEXT X 
RETURN 

REM **** PLACEMENT IN QUADRANT ARRAY **** 
R1 = FNAC8) 
R2=FNA<8) 

IF QCR1,R23#0 THEN 351 
RETURN 

PRINT LINO), "YOUR RESIGNATION HAS BEEN * ACCEPTED*" 
STOP 

PRINT "DO YOU NEED INSTRUCTIONS"; 
INPUT AS 
PRINT LINC 5) 

IF ASC 1, 13#"Y" THEN 440 
PRINT SPA<5);"<*> =ENTERPRISE" 
PRINT SPAC5),'" * = STAR- 
PRINT SPA(5),'" + + + =KLINGON" 
PRINT SPA(5);->!< =STARBASE" 
PRINT LINC2) 

PRINT "COMMAND = WARP OJGINES" 
PRINT "COURSE IS IN A CIRCULAR VECTOR AS SHOWN. " ; TAB( 50) ; "4 3 



"REAL VALUES MAY BE USED. 



368 PRINT 

369 PRINT "1-5 WOULD BE HALFWAY BETWEEN 1 AND 2. 
3700 PRINT TAB<48);"5 1 " 

37 10 PRINT "A 'WARP FACTOR' IS THE SIZE OF ONE QUADRANT. "; TABC 5 2) ,'"/ *\ " 



FOR EXAMPLE, ";TAB( 51); 
; TABC 52); 



372 


PRINT 


3730 


PRINT 


3740 


PRINT 


37 50 


PRINT 


376 


PRINT 


37 7 


PRINT 


378 


PRINT 


379 


PRINT 


300 


PRINT 


310 


PRINT 


320 


PRINT 


330 


PRINT 


340 


PRINT 


350 


PRINT 


360 


PRINT 


370 


PRINT 


38 


PRINT 


390 


PRINT 


3500 


PRINT 


3510 


PRINT 


32 


PRINT 


330 


PRINT 


340 


PRINT 


350 


PRINT 


360 


PRINT 


370 


PRINT 


38 


GOTO 4 


39 


END 



TABC 5 1),'"/ \" 

TABC50);"6 7 8" 

■COMMAND l=LONG RANGE SCAN" 

"CODED IN THE FORM XXX, WHERE THE UNITS ARE THE NUMBER" 

"OF STARS, TENS THE NUMBER OF STARBASES, AND HUNDREDS" 

"THE NUMBER OF KLINGONS. " 

LINC 2), "COMMAND 2=PHASERS" 

"YOU MAY DESTROY THE KLINGON BY USING ENOUGH PHASER" 

"POWER AS TO DEPLETE HIS SHIELDS. KEEP IN MIND THAT WHEN" 

"YOU FIRE AT HIM, HE GONNA DO IT TO YOU, TOO t " 

LINC2), "COMMAND 3 = PHO'rON TORPEDOES" 

"COURSE IS SAME AS WITH WARP ENGINES. THE LIBRARY" 

■COMPUTER CAN COMPUTE TRAJECTORY FOR YOU COPTION 1) - 

LINC2), "COMMAND 4=SHIELDS" 

-DEFINES THE AMOUNT OF ENERGY TO BE ASSIGNED TO SHI ELDS. " 

LINC2), "COMMAND 5=LIBRARY COMPUTER- 
OPTION 0=DAMAGE REPORT" 

" A STATE OF REPAIR LESS THAN ZERO INDICATES THAT" 

" THAT DEVICE IS TEMPORARILY DISABLED. " 
OPTION l = PHOTON TORPEDO DATA" 

- GIVES DIRECTION TO ALL KLINGONS IN YOUR QUADRANT. " 
OPTION 2=SHORT RANGE SCAN " 

- ALSO GIVEN AUTOMATICALLY AFTER SUCCESSFUL COMPLETION" 

" OF WARP ENGINE MANEUVERS. " 
LINC2), "COMMAND 6=RESI GNATION" 
LINC6) 
40 






109 



f ENGINES J 



890 



INPUT 
COURSE 




920 



INPUT 
WARP 
FACTOR 



940 



1030 



REPAIR 

SOME 
DEVICES 



1070 



RANDOMLY 

INFLICT 

DAMAGE 



1120 



MOVE 
ENTERPRISE 



1320 



1330 



INCREMENT 
STAR DATE 



1340 



690 



LEGAL \ NO 

COURSE 
? 



-/ COMMAND J 



Figure 4: Engines and 
navigation service routine. 
This routine is used to set 
the Enterprises 's course 
heading, speed (warp fac- 
tor), move the Enterprise 
to its new position, and 
simulate Klingon actions 
with randomly inflicted 
damages. Following execu- 
tion of this routine, the 
game normally returns to 
the command interpreter. 



Figure 5: Phaser firing command service 
routine. The purpose of this routine is to fire 
the phaser, calculate damages to the Klingon 
ship (if any), and give the Klingon a chance 
to fire back with the effects of damage to 
the Enterprise computed. 





-f COMMAND J 



^ENOUGH\ YES 
^ENERGY IN ^ 
^SHIELDS, 



1000 



2470 



f STOP J 




690 



is x 
WARP^\ YFq 
FACTOR <f^ 

P 



OUTPUT 
SHORT RANGE 
SCAN 




2470 



-J STOP J 



OUTPUT 
SHORT RANGE 
SCAN 



f COMMAND J 



INFORM 
USER 



-f COMMAND J 



-T COMMA 



ND J 



Trekkies Take Heart 

Recent news stories 
took note of the un veiling 
of the first production 
NASA Space Shuttle at 
Rock well In ter national's 
facilities in California. The 
impact of Star Trek is evi- 
dent: The name of the 
ship is "Enterprise. " (It is 
even complete with five 
general purpose but dumb, 
ie: voiceless, ship's com- 
puters and can't fly with- 
out them). 



1660 



INPUT AMOUNT 
OF ENERGY 
TO FIRE 




COMMA 



ND J 



FIRE 
PHASERS 



1770 




2050 



2090 



INFORM 
USER 



2070 



REMOVE 
KLINGONS 
FROM 
ARRAY 



2150 



\ ST ° P J 




f COMMAND J 



110 









between all of the Klingons in your quad- 
rant. Thus, if you fire 600 units, and there 
are two Klingon ships, you are in effect 
'firing 300 units at each one. Figure 5 shows 
the flowchart for the phaser firing sequence. 

Command 3 is for firing the photon 
torpedoes. To fire torpedoes, you must first 
know the direction to your target. This, like 
the navigation course, is determined on the 
circular vector shown in figure 3. The library 
computer can compute the torpedo trajec- 
tory for you. 

Often a star may be in your way, thus 



Table 1: Some of the variables described by 
function. These variables have unique uses 
as described. Not all variables are listed in 
this table. 



B3 
C$ 



E 
K3 



K9 

N 

P 

S 

S3 

T 
TO 

01,02 

S1,S2 
D(1)...D(6) 

G(1,1)...G(8,8) 
0(1,1). ..0(8,8) 

K(1,1)...K(3,3) 

K(l,1) 

K(l,2) 
* K(l,3) 
FNA(X) 
FND(O) 



The number of starbases in the 
current quadrant. 
String containing the current 
condition: red, green, yellow, 
or docked. 

Amount of energy remaining. 
The number of Klingon battle 
cruisers in the current 
quadrant. 

The total number of Klingon 
ships in the galaxy. 
Three digit number stating 
number of Klingons, starbases, 
and stars in quadrant. 
The number of photon tor- 
pedoes remaining. 
Units of energy currently 
assigned to shields. 
The number of stars in the 
current quadrant. 
The current stardate. 
The stardate on which the 
game began. 

Specifies the X and Y co- 
ordinates of the current quad- 
rant within the galaxy. 
Specifies the location of the 
Enterprise within the quadrant. 
Each element contains the 
state of repair for its respec- 
tive device, (ie: D(3) contains 
data for device No. 3). 
Each element is a three digit 
number containing data on a 
single quadrant of the galaxy. 
Each element is a number to 
4, specifying what type of 
object is situated in that 
sector of the current quadrant. 
Contains information on the 
Klingons in the current 
quadrant: 

The X coordinate of Klingon 
number I. 

The Y coordinate of Klingon 
number I. 

The shield power of Klingon 
number I. 

Returns a random number in a 
form useful to the program. 
Returns the distance from the 
Enterprise to another Klingon. 



preventing you from hitting your would-be 
victim. The only way around this, other than 
using phasers, which do not follow a pre- 
determined course and hence are not 
stopped by stars and other obstacles, is to 
use a small warp factor and maneuver in on 
the Klingon. Figure 6 shows the sequence 
that takes place when the photon torpedo 
command is initiated. 

Command 4 allows you to raise or lower 
the Enterprise's deflector shields. It is neces- 



(" PHOTON "\ 

TORPEDOES J 



J800 




I8IO 



Figure 6: Photon torpedo 
command service routine. 
This routine is entered 
when a photon torpedo is 
to be fired. It calculates 
the trajectory, examines 
the results for any Klingon 
hits, allows for Klingon 
return fire, then returns 
to the command routine 
if the Enterprise has 
survived. 



INFORM 
USER 



-f COMMAND J 



I830 



INPUT 

TORPEDO 

TRAJECTORY 




-f COMMAND J 



I860 



FIRE 
TORPEDO 




2I80 



INFORM 
USER 
TORPEDO 
MISSED 



YES 



2060 



2070 




YES 



INFORM 
USER 



REMOVE 
KLINGONS 
FROM 
ARRAY 



2 1 20 



YES 



2090 



2550 



HIT 
STARBASE 



2I50 



C 




2370 



KLINGONS 

RETURN 

FIRE 



2440 



YES 



J 







(command J 



111 






sary to be certain that your shields have 
sufficient energy before entering a combat 
area, because every time you fire at a 
Klingon, the Klingons fire back at you! 

To clarify, you are subjected to Klingon 
phaser fire every time you use phasers or 
photon torpedoes. The amount of energy 
the Klingons hit you with depends on how 
far away they are. For every unit that 



reaches you, your deflector shields drop a 
corresponding amount. If they drop to less 
than zero, you lose the game. You are given 
a short message within the short range scan i 
every time your shields get too low. You are 
also given a condition yellow whenever you 
get precariously low on energy. The 
sequence for raising the shield energy is 
given in the flowchart of figure 7. 



Listing 2: Sample outputs of the program in listing /. 



RJN 
STTR 



CD YOU NEED I NSTRUCTIONS?N 



COMBAT AREA CONDITION RED 

SHIELDS DANGEROUSLY LOW 



COMMAND! ?" 1 

8= SET COURSE 4 3 2 

}=LONG RANGE SCAN \ " / 

^PHASER CTRL \ / 

3=TORPEDO CTRL 5 

4= SHI ELDS . /"S 

^LIBRARY COMPUTER / " \ 

6=RESIGNATI0N 6 7 8 







+♦■+ * * 


ST ARDAT E 
COtO DI TI ON 


m 






* 


ENERGY 
TORPEDOES 


28 1 
13 






* 


SHIELDS 


442 






+++ +++ 

* 


KLINGONS 


24 




COMMAND: ?5 








COMPUTER ACTIVE AND AWAITING 


COMMAND? ] 








DIRECTION^ 7-99 










HRECTION = 7.74 










a RECTI ON= 7 










COMMAND:? 3 

TORPEDO COURSE (I-9):?7 






STARDATE 
CONDITION 
ENERGY 
TORPEDOES 


3000 

•RED* 
3000 
15 



***KLINGGN DESTROYED*** 
24 UNIT HIT ON ENTERPRISE 
28 UNIT HIT ON ENTERPRISE 

COMMAND: ? 1 






SH I ELDS 






KLINGONS 


£6 


: 0:2:5: 







:205 : 5 
: 3 :2 02 



COMMAND: ?0 

COURSE < 1-9): ? 0_ 1 

VfcRF FACTOR ( 0-8) : ?3 



COMMAND: ?4 

HSIERGY AVAILABLE= 3 000 

NUMBER OF UNITS TO SHI ELDS:? 50 

COMMAND: ?5 

COMPUTER ACTIVE AND AWAITING COMMAND?-! 



SHIcLDS 
KLINGONS 



FUNCTIONS AVAILABLE FROM COMPUTER 



0=DAMAGE REPORT 



COMPUTER ACTIVE AND AWAITING COMMAND?! 



II RECTI ON= 7.? 

HRECTlOi\)= 7 

COMMAND: ?3 

10RPEDO COURSE (J-?):?7 



COMMAND: ? 1 




: 205 : 4:103: 




: 4 : 3 : 5 : 




: 13 : 1 : 4 : 




COMMAND: ?0 
COURSE ( 1-9) : ?6 

VARF FACTOR (G-8)i 


: ? 1 



COMMAND: 7 3 

TORPEDO COURSE C 1 - 9 ) : ? 7 . 9 

MX) CAN'T DESTROY STARS; SIl,LY! 

'lORPEDO MI SSED 
22 UNIT HIT ON ENTERPRISE 

COMMAND:? 2 

ENERGY AVAILABLE^ £50 

NUMBER OF UNITS TO FIRE:?30ii 
8 6 UNIT HIT ON KLINGON 

13 UNIT HIT ON ENTERPRISE 

COMMAND: 72 

2JERGY AVAIL ABLE= 170 

fJUMBER UF UNITS TO FI RE: ? 1 



NUMEER OF UNITS TO FIRE:?40G 
43 UNIT HIT ON KLINGO.N 

«**KLINGON DESTROYED***' 
COMMAND: ? 1 



: : 

~5~r"~7 



STARDATE 


3003 


CONDITIO 
ENERGY 


DO CK ED 
3000 


TORFELOLS 
SHI ELLS 


J s 


KLINGONS 


23 



COMMAND: ?0 








COURSE C 1-9) :?3 

VARF FACTOR ( 1-8) : ?2 








COMBAT AREA CONDITION 
SHIELDS DANGEROUSLY LOW 


RED 






<*> * * 








+ + + 




STARDATE 


3004 






CONDITION 
ENERGY 


♦RED* 
2989 


* 




TORPEDOES 
SHIELDS 


15 



* ♦ + + 




KLINGONS 


23 


* 









2 UNIT HIT ON ENTERPRISE 

***THE ENTERPRISE HAS BEEN DESTROYE 



COMBAT AREA 



CONDITION RED 



'HE FEDERATION WILL BE CONQUERED!!! 



DONE 
R 



112 



Command 5 allows the user access to the 
library computer which has three options 
.specified by an integer between zero and 
two. If you enter an illegal option, such as a 
negative number, the computer will print a 
short list of commands. 

Option gives a damage report. The 
Enterprise may get damaged when you 
warp out at high speeds. When this 
occurs, you are informed as to which 
device has been affected. Extensive 
damage to a device may render it 
inoperable. In the damage report, each 
device is listed along with its respective 
state of repair. A state' of repair less 
than zero indicates that the device is 
temporarily disabled. 
Repairs are made, albeit slowly, by 
onboard technicians, but a faster way 
is to dock with a starbase. Not only 
does this automatically repair your 
ship, but you are also resupplied with 
energy and photon torpedoes. An 
extra bonus: While docked, you are 
protected from Klingon attack by the 
starbase's shields. 

Option 1 calculates the torpedo trajec- 
tory to all Klingons in your quadrant. 
Option 2 prints range scan. If you are 
docked with a starbase, it also replen- 
ishes your supplies. 



f SHIELDS J 



2200 



PRINT 

AVAILABLE 

ENERGY 



22I0 



INPUT 

ADDITIONAL 
SHIELD 
POWER 



2230 



2260 



YES 



RESET 
SHIELDS 



LEGAL \ NO 
INPUT 
P 




-/ COMMAND J 



f COMMAND J 



Figure 7: Shields service 
routine. This routine up- 
dates a power level for 
the Enterprisers shields. 



Command 6 indicates that you wish to 
resign. Other good ways to end the game 
prematurely are to torpedo a starbase, or 
allow yourself to run out of energy. 

Conversion Notes 

As everybody knows, the growth of the 
personal computing field has been con- 
stantly hampered by the problem of stan- 
dards. This has been particularly bothersome 
in the software agenda, where there are said 
to be no fewer than forty different versions 
of BASIC floating around. Consequently, I 
thought it would be appropriate to comment 
on some of the difficulties one might 
encounter in the conversion process. 

Many BASICs have explicit matrix 
manipulation features. In particular I used 
MAT . . . ZER extensively. This statement 
initializes all the elements of a specified 
matrix to zero. It also allows the pro- 
grammer to redimension the matrix. 

LIN(X) appears in several places within 

the program. LIN is an output control 

■^function similar to TAB, which generates X 

number of linefeeds every time it is 

encountered. 

GO TO. . . OF is replaced by ON ... GO 
TO in many BASICs. 



Substrings in the form X$(1,x) are 
replaced by the construct LEFT$(X$,x) in 
Altair BASIC. Also, Altair BASIC does not 
require that strings be dimensioned. 

PRINT USING is used to format the long 
range scan. Output should appear in the 
following form: : xxx : yyy : zzz : The 
values of xxx, yyy, and zzz are the status 
reports concerning the number of Klingons, 
starbases and stars discussed under command 
1. 

The symbol # is used to express 
inequality within IF... THEN statements. 
Also, matrix subscripts are surrounded by 
brackets rather than parentheses. Near the 
beginning of the program, the sequence 
A=B=C=. . . is used to initialize many vari- 
ables to the same value. This may produce 
unpredictable results on some machines. 

The memory requirement of this particu- 
lar version of Star Trek is 10 K bytes, plus 
interpreter. The program itself is 9382 bytes 
long. If your computer has an integer vari- 
ables option, by all means use it. It can save 
you over 300 bytes on the matrices alone. If 
you are cramped you can also delete the 
instructions from the program. To do this, 
simply delete statement 350 and lines 3570 
through 3980." 



Positively Baker Street 

Here is the solution to 
the "Baker Street Irregu- 
lar" which appeared on 
page 86 of the February 
1977 BYTE. 



| W®\ 



iflLlelillEE] 

IktalskfeEIil 



» 



h 



a : s Sjb ; 

[I TolwIprclP l \ ,'. I ej If 

''*'" tI i E 

HJffl 






fWIL 






113 













ffffntllH* 5 rum ii 1 1 1 1 i Till 




M 



Photo J: The typical 
board in a Digital Group 
kit comes in a sea fed plas- 
tic bag with two compart- 
ments. One compartment 
contains the board and the 
second contains the neces- 
sary parts. 



Steve Ciarcia 

Box 582 

Glastonbury CT 06033 



Try This Computer on for Size 



There arc a number of fine micro- 
processor system kits available lo the home 
computer enthusiast. One such system, 
which I just recently assembled, is the 
Digital Group 8080A. This microcomputer is 
marketed by the Digital Group in Denver 
CO. This concern, with Dr Robert Sliding as 
its resident genius and designer, offers in my 
opinion the highest price performance of 
any home computer available. The Digital 
Group is somewhat unorthodox by not 
jumping on the bandwagon and being Altair 
bus compatible but their unit contains 
enough bells and whistles to placate even the 
most demanding computer owners. 

This system, as is true of most others, has 
its good and bad points. I am an electrical 
engineer well versed in digital design and 
have been closely following the microcom- 
puter scene since the advent of the MARK-8 
in 1974. I have a Scelbi 8B and have helped 
friends build Altairs and IMSAIs from kits 
and feel that I can be completely objective. 
It is of course extremely difficult to restrain 
laudatory comments when one is so well 
satisfied, but bear with me. 

The Digital Group sells a basic computer 
system which can contain one of four proc- 
essor chips: the Zilog Z-80; AMD 8080A; 
MOSTEK 6800; or a MOS Technology 6502. 
I chose the 8080A because of a combination 



of price and software availability. The Digi- 
tal Group System (DGS) is generally sold as 
a three board system with mother board. 
This three board microcomputer has the 
following functions and specifications. 

Processor Board 
AMD 9080A 
2 K bytes programmable memory 

and EROM bootstrap loader. 
Direct Memory Access (DMA) logic. 
8 level hardware vectored interrupt. 
Buffered address and data bus lines. 
16 bit (64 K) addressing capability. 
Input Output Board 

Four 8 bit parallel input ports. 
Four 8 bit parallel latching 
output ports. 

Full 16 bit port addressing. 
TV Readout and Cassette 
Interface Board 
Video Readout: 

Software controlled cursor. 
51 2 characters organized as 
16 lines by 32 characters. 
7 by 9 character matrix. 
Full 128 ASCII character set. 
Upper and lower case alphabet. 
Math symbols. 
Special symbols. 
Greek alphabet. 



114 



Direct video output. 
Cassette Interface: 

Uses standard cassette recorder. 
FSK recording technique. 
Wide shift Teletype frequencies. 
Operates at 1100 bps. 
Utilizes "software UART." 

An additional 8 K programmable memory 
board is added to the three board set and is 
sold to make a four board set. The specs on 
the programmable memory areas follows: 

8 K Static RAM Board 

Uses 2102-1 parts with 

500 ns access time. 
No wait states. 
Buffered address lines. 
Address decoding covers full 

64 K range. 
Power consumption 2 A at 5 V. 

There arc many variations of the basic 
system as described, and this listing is only 
representative of their total offering. In- 
terested parties should contact the Digital 
Group at POB 6528, Denver CO 80206. 

As I mentioned previously, I had been 
following the DG since they entered the 
microcomputer scene. Their first offering 
was a simple 300 bps "el cheapo" cassette 
interface which met absolutely nobody's 
standard. While everyone was arguing Kansas 



City and all the rest, I built this for $6 and 
had it operational in three hours. I have 
always been action oriented and all the 
talking in the world won't put your system 
on line. I have grown to expect and accept 
the unorthodox from the Digital Group. 

Other manufacturers sell basic bare bones 
systems for prices starting around $600. For 
this price they contain a fancy case and 
front panel, gigantic overkill power supply, 
and a processor board with ancil Maries. 
There is no memory, IO, or mass storage 
capability: These are all extra cost options. 
Minimum capacity machine language and 
cassette storage system can approach $800 
to $900. I affectionately refer to this nickel 
and diming as an "arm and a leg turnkey 
system." 

The DGS is a profitmaking venture, I 
assure you; but it appears to have pricing 
and design philosophies which in my opinion 
better meet the needs and requirements of 
the knowledgeable experimenter. 

When one buys a DGS three or four 
board system, you get Digital Group's ver- 
sion of the logically complete product: a 
system which in its basic price has no case, 
power supply or front panel. These are 
available from DG and can be purchased of 
course by the affluent or built from scratch 
by the frugal. Add a power supply, a video 
monitor salvaged from an old TV, a surplus 



Photo 2: The author's Digital Group 8080 processor card. The actual processor is an AMD 9080 A, one of the second sources of 
the original Intel 8080 design. The crystal which controls the processor clock is at the lower right, and the 2 K byte section of 
memory on the card is represented by the two rows of eight sockets at the left edge of the card. A UV erasable ROM chip 
(marked "80 A " with a felt tip pen on the top edge at left of center) contains systems software which eliminates the need for a 
formal "blink in ' lights " front panel. 





Photo 3: The author's Digital Group System 8 K byte memory card. The card contains 64 memory integrated circuits (in two 
arrayed segments) and in the center are various miscellaneous circuits used to interface the backplane bus of Digital Group 
system. 



ASCII keyboard, and a decent cassette re- 
corder; and you are in business with a 
complete functioning microcomputer. 

I had been hearing this rhetoric and 
receiving DGS flyers for a while. Then I 
decided to take the plunge. I called DGS one 
morning in mid 1976 and ordered the four 
board 8080A system with standard mother 
board. Since this four board set contains 
10 K bytes of programmable memory and is 
capable of supporting an Extended Tiny 
BASIC, I ordered the TBX software for $5. 
The total 10 K system as ordered was $645. 
Literature supplied by DGS quoted 30 clay 
delivery but I had resigned myself to the 
possible two month wait that friends were 
experiencing with other companies. When 
the complete package arrived three weeks 
later I was ecstatic and set out immediately 
to the. task of getting "on line." 

The packing material, though sparse, was 
adequate; and, since there were no heavy 
components like transformers, its lack was 
inconsequential. Like any kit builder, I 
expected the first project would be to 
separate the pile of parts and boards and to 
sort components out among the respective 
boards. Anyone who has ever experienced 
sifting through a pile of resistors until their 
eyes cross can appreciate what I am saying. 
Fortunately this was unnecessary. Each 
board is packaged in a two compartment 
scaled plastic bag. One side contains the 
blank printed circuit board and the other 



contains all the integrated circuits, sockets, 
and other components as seen in photo 1. 
When unpacking, two things are immediately 
apparent. The boards are top quality with 
plated through holes and there are no 
jumpers. 

I searched through the box looking for 
the usual last minute revision sheets and 
tackons but there were none. This appar- 
ently was a final design with absolutely no 
"kluge rigging" necessary to make it work. 
The Digital Group flyers indicate they do 
not sell interim designs nor advertise any- 
thing for sale until it is available "off the 
shelf." From my experience, this appears to 
be the truth. 

The ease of construction of this system is 
a function of the particular board being 
assembled. I'll cover each board separately, 
but a word of caution first. The Digital 
Group System is not and should not be 
considered in the same realm as a Heathkit 
or similar undertaking. Hardware documen- 
tation is adequate and descriptive but is not 
as detailed pictorially as a Heathkit. This is 
not a kit but rather an unassembled micro- 
computer. Its construction should be at- 
tempted by the experienced kit builder only. 
If necessary, build several difficult Heathkits 
first to gain experience with electronics 
components and assembly. At the least, 
difficult assemblies should be purchased as 
fully assembled and tested units and the 
other cards carefully constructed. 



116 



Building the Processor Board 

The processor board is of course the heart 
of the microcomputer. This card contains 
the microprocessor itself and supporting 
components. It is shown (after I assembled 
it) in photo 2. The Digital Group has sought 
to learn from the experiences of other 
manufacturers and builders and has ob- 
viously benefited. The most notable addition 
is the incorporation of integrated circuit 
sockets throughout. Even with the use of 
prime components, bad circuits are possible. 
The average hobbyist may have considerable 
experience doing the initial soldering, but 
unsoldering an integrated circuit is quite 
messy. Using sockets adds the capability of 
quickly changing a suspected bad com- 
ponent without cither destroying the inte- 
grated circuit or the printed circuit board. 

Significant effort and thought has been 
put into this microcomputer design as is 
evident in the system architecture of the 
processor card. The microprocessor is driven 
by a crystal controlled clock which exhibits 
none of the frequency instability of multi- 
vibrator controlled clocks. Crystals arc cur- 
rently used in most microprocessor systems 
for their "rock like" stability. In addition, 
there is 2 K of programmable memory on 
the board which can be selected to respond 
to any two consecutive 1 K positions in 
memory address spaces. For startup and 
checkout, this memory should be set for 
to 2 K allowing the user to perform limited 
machine language programming without ad- 
ditional memory. I'll cover the procedure for 
checkout a bit later. 

There are of course other goodies on this 
card. Direct Memory Access (DMA) and 
priority interrupt hardware is provided as a 
user option. The basic three and four board 
systems include test procedures for the 
interrupt request logic but DMA checkout is 




Photo 4: The author's Digital Group System 10 card. This card interfaces to 
the system's bus, providing four parallel output ports and four input ports. 
These ports are routed to the backplane where they communicate to the 
video display, keyboard and cassette interfaces. 



left for the brave of heart and is not 
addressed here. In addition to this circuitry, 
a 1702A EROM containing the tape cassette 
bootstrap loader is located in Page of 
memory. When power is turned on, a power 
on reset signal initializes the system and 
reads in the operating system cassette. More 
on this later. 

The Digital Group System bus structure is 
similar but differs in detail from that of the 
Altair. Robert Suding's publicized phil- 
osophy dictates an interchangeable processor 
capability which hopefully decreases the 
obsolescence of the total system. As new 
and more powerful microprocessors such as 
the Z-80 come on the market, a new 
processor card should be interchanged with 
the bus of the older unit while not affecting 
the rest of the system. To accomplish this 
goal, the Digital Group system uses unidirec- 
tional address and data buses as in the 




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117 







Photo 5: The cassette and 
CRT interface board. This 
board contains the video 
signal generation and 
audio processing circuits 
of the Digital Group Sys- 
tem. | For more detailed 
descriptions, see the July 
and August 1976 issues of 
BYTE.| 



Altair. Such a bus structure, as has often 
been seen in the marketplace, is easily 
adapted to any 8 bit processor. There is of 
course a basic disadvantage to owning a 
unique backplane pinout, that of having 
only a single source. Every microprocessor 
manufacturer knows that few designers will 
tic themselves to a single source part. That is 
the reason you see so many different com- 
panies producing 8080s. The Altair bus has 
been widely second sourced, which has led 
to some fierce competition resulting in 
modest benefits to the buyer. Obviously the 
small system owner does not have the same 
constraints as the high volume manufacturer 
but he should be aware of the lack of price 
competition and interchangcability when it 
comes to memory and IO card expansion. 
The Digital Group is apparently aware of 
their unique position and has sought to 
dispell concern by selling blank IO and 8 K 
memory boards at a very reasonable price. 
This allows the user to shop around for the 
best 2102-1 memory prices. 

Since the DGS has no front panel, the 
processor card cannot be checked out easily 
by itself. But then no real functional test of 
a processor system as a whole can be easily 
performed with a front panel, either. The 
rest of the system must be constructed to 
perform the necessary diagnostics. 

Assembling the Memory and IO Boards 

Both the 8 K memory and parallel IO 
boards are constructed in a very straight- 
forward manner. Again all integrated circuits 
are socketed and literature supplied is both 



explicit and clear. The memory board (sec 
photo 3) and components supplied to me 
contained premium grade AMD 2102-1 
parts. With these parts no wait states are 
required and the processor runs at full rated 
speed. 

The IO card which contains four parallel 
inputs and four latched parallel outputs 
must be set to the lowest order addresses 
when only one IO board is in the system. 
This is because the video display generator, 
keyboard and cassette interface are directly 
wired to IO ports on this card through the 
mother board. The ports arc address select- 
able; but to utilize the DGS operating 
system software, the addresses must be set as 
described in the DGS write up. Additional 
memories or IO can have addresses to suit 
the user. 

Assembling the Cassette and 
CRT Interface Board 

This board is the external communica- 
tions medium of the Digital Group micro- 
computer. Since the DGS has no front panel, 
it is solely dependent upon a video based 
operating system utilizing the video display 
generator interface and a television monitor, 
or modified television. The software for such 
an operating system is about 1.5 K and 
cannot be entered except through the cas- 
sette interface. I should clarify one thing 
though. The DGS which I purchased is quite 
amenable to front panel hookup. The three 
and four board units sold by the Digital 
Group do not incorporate front panels but 
they do provide a design for one. Obviously, 



118 









if a user builds a DG system and both his 
processor and video display sections fail to 
function properly, he is dead in the water 
and would have to build the front panel. The 
design is neat and functional and plugs into 
any spare memory card slot. If, on the other 
hand, the user is thoroughly frustrated, 
suspect boards can be returned to DG for 
troubleshooting according to a price sched- 
ule supplied with the unit. 

Now that you know how to get yourself 
out of the hole if it happens, I'll explain the 
proper method of digging. 

The CRT and cassette interface sections 
are assembled using the same methodical 
approach as the other boards. The literature 
is very good in this respect. The problems 
come in calibration. The CRT is fairly 
straightforward, it cither works or it doesn't. 
There are no adjustments. This section, 
when completed, is plugged into the mother 
board, attached to a monitor, jumpered as 
per the testing procedure, and powered up. 
If it works the screen will be immediately 
filled with 512 random characters. These 
characters include upper and lower case 
alpha symbols, and Greek lettering. When 
this works you are half done with the check 
out of the card. 

Being half done in this case is not nearly 
enough. The assembly of the cassette inter- 
face is simply a matter of following direc- 
tions but calibrating it is a bit of a task. 
There are operating system options which 
allow the computer to function as a fre- 
quency counter, but that is a little further 
downstream. To properly adjust the cassette 
interface, a scope, a frequency counter, an 
accurate DC voltmeter or DVM and a vari- 
able frequency oscillator are required. I 
fortunately have all this equipment, but not 
everyone's spouse is as understanding as 
mine. The frequency source is set to 1 V 
p to p at 2125 Hz and applied to the inter- 



I READ Cassette 
Z WRITE Cassette 

3 TV Storage Dump 

4 Keyboard Program 

5 Interrupt Tester 

6 Memory Tester 



face input, simulating the tape recorder 
output. Using a scope to determine the point 
of peak response, the active filters are 
adjusted correspondingly. This procedure is 
repeated for 2975 Hz. Next the comparator 
which detects whether the input frequency 
is at a mark or zero is adjusted to switch 
cleanly as the frequency source sweeps 
between the two valves. That takes care of 
the receiver sections. 

The FSK (frequency shift keyed) modula- 
tor is a single VCO (voltage controlled 
oscillator) chip which switches between two 
frequency values corresponding to TTL one 
or zero inputs. In initial checkout, a voltage 
(3.5 V) simulating a TTL level one is applied 
to the control line of the oscillator and the 
output is adjusted to 2125 Hz. The control 
line is then grounded and the output ad- 
justed to 2975 Hz. If this can be accom- 
plished satisfactorily, you're in business. 

System Checkout 

When all of the cards are assembled, and 
the solder splashes cleaned off, take one last 
look at each card. Remember, this is the 
smoke test. 

Attach the power supply to the mother 
board and with no boards inserted and the 
power on, check that the proper voltages arc 
present. Shut off the supply and insert the 



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119 



processor, 10 and CRT cards. Cross your 
fingers and turn on the power. If all works 
correctly, the screen will display: "READ 
8080 INITIALIZE CASSETTE". Success- 
fully accomplishing this means that the 
processor is operating correctly, the CRT 
board works fine and at least part of the 10 
board is functioning. 

The acid test is loading the operating 
system via the cassette interface. (To facili- 
tate this endeavor and add more ease of 
operation, a Reset/Run button should be 
wired to the mother board as described in 
the DG literature.) With this message present 
on the screen, insert the 8080 operating 
system cassette and hit the play button. 
Adjust the output level to be about 1 V 
p to p and soon a leader tone should be 
heard. No change should appear on the 
screen. Immediately following the tone will 
be the asynchronous data at 1100 bps. 
Proper reception of this data will be evident 
on the video display. As each byte of data is 
processed and loaded into memory, it is read 
from memory to verify that it got there. If it 
loaded correctly, a number corresponding to 
the high order digit of the octal page address 
of this byte location is printed on the screen. 
With 256 bytes per page, there will be 
256 number 1s, 256 number 2s, etc, until 
the tape is loaded. Should the memory 




Photo 7: A view of Steve's assembled Digital Group System. [When a party 
from the BYTE office stopped by at Steve's basement laboratory in 
Connecticut on the way back from Atlantic City last fall, we found his 
system up and running as pictured here, with his older Scelbi 8B computer 
acting as a slave peripheral processor to control the vector graphics output 
device described on page 78 of the November 1976 BYTE. Steve cooked an 
excellent Quiche Lorraine for dinner that night while Dan Fylstra and I 
explored a game of KINGDOM running in Tiny BASIC . . . CH | 



check signify a bad byte, a period (".") will 
be displayed instead of the octal number. 
It's a good idea to watch the screen while 
the cassette is being read. 

If the cassette was read in properly, the 
computer will display the operating system 
options on the screen as in photo 6. If not, 
try again. Be careful to watch that there arc 
no numbers, signifying received data bytes, 
on the screen prior to the playback of the 
actual data on the tape. Should this occur 
due to a noise glitch, hit the reset, and it will 
clear this problem. 

The DGS operating system requires that 
alphanumeric information be input on a 
parallel 8 bit input port in the form of 
ASCII. All this means is that you need a 
keyboard. The ASCII is 7 bits of the input 
port and the eighth bit corresponds to the 
key pressed or strobe signal. The operating 
system scans this bit looking for a transition 
from a zero to a one so therefore it must be 
a positive going strobe (TTL level) with a 
minimum duration of 50 jus. I have a surplus 
Sanders Associates 720 keyboard which a lot 
of people have. This keyboard has a 5 jus 
negative going strobe though and must be 
modified by adding a oneshot such as a 
74121 to it. Since the whole keyboard runs 
on 5 V, this is an easy conversion and the 
keyboard is an exceptional buy. With key- 
board and monitor, the system is totally 
operational. If you were able to get the 
operating system option list which appears 
in photo 6, you are ready to go. Hit 3 and 
the screen displays the contents of all the 
registers and flags. Hit space and you'll start 
to page through memory displaying all 
memory contents. Return to the operating 
system and hit option 4 and the keyboard 
can be used to enter octal machine language 
code anywhere the user desires. The com- 
plete explanation is included with operating 
system tape. 

Where the Digital Group System really 
shines is the cheap software and system 
simplicity. Add the 8 K memory board, set 
the address for to 8 K and reset the 
processor 2 K memory to occupy 8 K to 
10 K and we are ready to run Extended Tiny 
BASIC. 

With 10 K of memory installed, turn the 
system on and start the 10 K Tiny BASIC 
tape as you would the operating system 
tape. After a few minutes the tape will have 
been read and the system will display the 
Tiny BASIC options: 

TINY BASIC 

1. READ BASIC PROGRAM 

2. WRITE BASIC PROGRAM 

3. DISPLAY COMMANDS 



120 



4. DISPLAY ERROR CODES 

5. CONTINUE PROGRAMMING 

6. TINY BASIC 

With these options, an Extended Tiny 
BASIC, created by Dick Whipple and John 
Arnold and described in the January 1976 
issue of Dr Dobb's journal of Computer 
Calisthenics and Orthodontia, is ready to go. 
Buy a couple of simple programs such as 
Blackjack, Bantum and others from the 
Digital Group Software Systems, and you 
can utilize the computer immediately to 
entertain the whole family or bone up on 
Tiny BASIC and write your own programs. 

Observations and Criticisms 

As stated earlier, it is my opinion that the 
Digital Group System is one of the best 
offerings on the small systems market today. 
But as previously mentioned, anyone not 
having the proper equipment should not 
attempt to assemble the CRT and audio 
cassette interface. After receiving my sys- 
tem, I was up and running with the 2 K 
processor card memory with two evenings' 
work. Since I had the equipment and am 
very receptive to logical well written instruc- 
tions, I had no troubles. My cassette inter- 
face didn't work at first, and I discovered 
that it was because of insufficient tape 
recorder bandpass. I had hoped to use the 
same el cheapo recorder that I used for my 
previous 300 bps interface, but no way. I 
rushed out and spent a whopping $39 for a 
new one from J C Penney which had been 
suggested by another Digital Group System 
owner. The first time I hit play, it worked 
perfectly. Since that time, I have discovered 
that the cassette interface is sensitive to both 
volume and tone settings during playback. 
This is probably only a function of the tape 
recorder I own and is not necessarily indica- 
tive of a general problem. Using a quality 
cassette recorder of the type suggested by 
the Digital Group should eliminate any 
playback problems. 

Recording a program on tape is simply a 
matter of choosing the correct operating 
system option but getting accurate mark and 
zero frequencies may require minor tweek- 
ing. There appears to be some shift in the 
output frequencies from the time of the 
static calibration and actual dynamic opera- 
tion. This is obviously due to the fact that 
3.5 VDC and V are not the actual TTL 
levels applied to the voltage controlled 
oscillator. A VCO is an analog device and 
not all TTL chips are exactly alike. After 
reading in the operating system tape I 

Continued on page 129 



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121 






Multiplex Your Digital LED Displays 



James Hogenson 

Box 295 

Halstad MN 56548 



Digital LED displays were once a novelty 
to the hobbyist, a luxury found in expensive 
lab equipment. They are now a household 
word and a useful tool for the digital 
experimenter. A digital LED display can be 
used as the readout for almost any test 
instrument. A programmable LED display 
can be used as a computer output. A digital 



LED display is a handy replacement for the 
binary lights on a computer control panel. If 
you have been thinking about using an LED 
display for any of these or other reasons, 
this article may save you some time, money, 
and power. 

There are two methods which may be 
used to drive an LED display. The direct 



Figure 1 : Circuit diagram 
of a simple multiplexed 8 
digit display for BCD or 
octal data. The printed cir- 
cuit layout of this version 
is depicted in figure 3. 
Figure 5 shows the printed 
circuit used to mount the 
displays. 



Integrated Circuit Summary List 







POWER 


PINS 




Type 


+5 V 


GND 


IC1 


7493 


5 


10 


IC2 


74151 


16 


8 


IC3 


74151 


16 


8 


IC4 


74151 


16 


8 


IC5 


74151 


16 


8 


IC6 


7448 


16 


8 


IC7 


75451 


8 


4 


IC8 


75451 


8 


4 


IC9 


75451 


8 


4 


IC10 


75451 


8 


4 


IC11 


74155 


16 


8 


IC12 


555 


See figure 1 





TO SEGMENT LINES 

OF ALL B LED DISPLAYS 



NOTE: 8 MAN 4 or DL704 seven segment LED 
displays are required. 




DDDDDDDD 
8 7 6 5 4 3 2 



DATA INPUTS FROM PARALLEL OUTPUT PORT 



122 



power configuration uses one 7 segment 
driver for each 7 segment LED in the 
display. Constant power is supplied to all 
digits. The multiplexed configuration uses 
only one 7 segment driver for several digits. 
Power is supplied to only one digit at a time, 
but is switched at a high rate so all digits 
appear to be on constantly. Since only one 
digit is powered at any given time, a certain 
amount of power is saved. This principle is 
widely used in electronic calculators. 

The circuit of figure 1 is the driver circuit 
for an 8 digit multiplexed LED display. This 
circuit will display 8 digits of parallel BCD 



data. All data inputs are connected to a 
multiplexer. There is one 8 channel multi- 
plexer for each of the 4 data input bits. The 
least significant bit of each digit is connected 
to an input of IC2; the most significant bit 
of each digit is connected to an input of IC5, 
etc. The multiplexers and demultiplexer are 
addressed by the 7493 counter which is 
incremented at approximately 4 kHz by the 
555 oscillator. IC11 is connected for 3 to 8 
line demultiplexing. When the selected out- 
put line of the demultiplexer goes to a low 
state, one of the peripheral interface gates is 
enabled. IC7 through ICIO are dual peri- 



I integrated Circuit Summary List 







POWER 


PINS 




Type 


+5 V 


GND 


IC1 


555 


See figure 2 




IC2 


74123 


16 


8 


IC3 


74193 


16 


8 


IC4 


7489 


16 


8 


IC5 


7404 


14 


7 


IC6 


7448 


16 


8 


IC7 


75451 


8 


4 


IC8 


75451 


8 


4 


IC9 


75451 


8 


4 


ICIO 


75451 


8 


4 


IC11 


75451 


8 


4 


IC12 


75451 


8 


4 


IC13 


75451 


8 


4 


IC14 


75451 


8 


4 


IC15 


74154 


24 


12 



Figure 2: Circuit diagram 
of a digit-serial multi- 
plexed 16 digit display 
with memory. The printed 
circuit layout of this ver- 
sion is depicted in figure 4. 
Figure 5 shows the printed 
circuit (two copies re- 
quired) used to mount the 
displays. 



NOTE: 16 MAN 4 or DL704 seven segment LED 
displays are required. 



RI6 +5V 
2 IK 







XII XIO ' X9 XB X7 X6 X5 X4 

DIGIT DRIVES TO COMMON CATHODES OF DIGITS TO 15 



123 






Figure 3a: Printed circuit pattern (foil side) of the 8 digit display circuit. 



nagaBQO 




#e-|^ 



pheral interface gates. Each gate is capable 
of sinking a current of up to 300 mA. When 
a digit is selected, the interface gate provides 
a ground path for the common cathode of 
the 7 segment LED. Only the LED whose 





„■,,»»«* ww--* 






4^' ; ^ i^fV- \fW 


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1 f. 


# : -: ; |:|; 










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Ptoto 7; A 16 digit BCD assembly constructed using the circuit of figure 2, 
with the printed circuit layouts of figures 3 and 5. The J 6 digit memory 
display requires two copies of the LED mounting board, with jumpers 
connecting the segment lines from one board to the next. Power, data and 
address inputs are shown trailing away at the bottom. 



cathode is grounded will light up. Although 
the same data will be present at all digits, the 
data will be displayed by only one digit. By 
changing the data present and switching the 
enabled digit, each digit will display its own 
data. A 7448 decoder/driver converts the 
BCD data to a 7 segment code and drives the 
individual segments of the LEDs. The seg- 
ments of all 8 digits in the display are 
connected in parallel. 

The circuit of figure 2 is a 16 digit 
programmable display. This circuit will 
memorize and display the data presented at 
its inputs one digit at a time. The size of the 
demultiplexer and the number of peripheral 
interface gates is doubled, since the pro- 
grammable display has 16 digits. The input 
multiplexer is replaced by a memory which 
is loaded digit by digit. The 7489 TTL RAM, 
IC4, is very conveniently arranged for a 1 6 
digit BCD memory. The RAM outputs are, 
however, inverted open collector outputs, so 
pullup resistors and inverters (IC5b to IC5e) 
are needed. 

The counter used is a 74193 presettable 
binary counter, IC3. A 555 oscillator (IC1) 
drives the counter at 4 kHz. A digit is 
selected for programming by setting the 
memory address at the inputs of the coun- 
ter. An external clock pulse at the clock 
input will program that digit. It is assumed 
the external clock pulse will be at least 200 
ns. When the clock pulse input line goes low, 



124 






Figure 3b: Printed circuit component side map of the 8 digit display. See figure I for identification of 
components, jumper wires are shown as dotted lines in the overlay. 



SEG. DRIVE 
OUTPUTS TO 
DISPLAY 
BOARD(S) 

f gabcde 



DIGIT DRIVE OUTPUTS 




+5V 



GND 



the counter will be disabled and the address 
on the counter inputs will appear at the 
outputs addressing the memory. IC2 pro- 
vides a 60 ns delay, then a 60 ns pulse which 
writes the data at the memory data inputs 
into the memory location addressed. When 
the clock line returns to the high state, the 
counter will resume counting. The counter 
sequentially addresses the BCD data stored 
in the memory while it selects and enables 
the appropriate digit in the display. 

Single layer printed circuit patterns are 
provided for readers who make their own 
boards. The inputs on the simple multi- 
plexed driver board (figure 1 schematic, 
figure 3 printed circuit layout) are con- 
nected as follows: Bit of the first digit to 
input A0, bit 1 to input BO, bit 2 to input 
CO, bit 3 to input DO, bit of the second 
digit to input A1, bit 1 to input B1, etc. The 
segment outputs (a to g) should be con- 
nected to the display board (see figure 5b) at 
the pads provided on either end of the 
board. The digit (common cathode) driver 
outputs (X0 to XI) should be connected to 
pin 4 of their respective digits. 

Output connections for the 16 digit 
programmable display driver board (figure 2 
schematic, figure 4 printed circuit layout) 
are the same as for the self scanning board. 
Referring to the component placement dia- 
gram, connect the BCD data input directly 
to the Dq, D-|, D 2 , and D^ lines of IC4. The 



mm mm m mmmw®*** • 

^iUfi Miam ' >muj£. jj^w M'MK '!4ttMfc ^^^ 

uM^t ^uaij jyiiir jrnHj- j^^ -f .^^^ ^h^M 

mmMfmmmm 



The Tarbell Cassette Interface 

• Plugs directly into your IMSAI or ALT AIR 

• Fastest transfer rate: 187 (standard) 
to 540 bytes/second 

• Extremely Reliable — Phase encoded 
(self-clocking) 

• 4 Extra Status Lines, 4 Extra Control Lines 

• 25-page manual included 

• Device Code Selectable by DIP-switch 

• Capable of Generating BYTE/LANCASTER 
tapes also. 

• No modification required on audio cassette 
recorder 

• Complete kit $120, Assembled $175, 
Manual $4 

TARBELL ELECTRONICS 

144 Miraleste Drive #106, Miraleste, Calif. 90732 

(213)832-0182 

California residents please add 6% sales tax 



125 









Figure 4a: Printed circuit pattern (foil side) of the 16 digit memory display circuit. 




digit address input lines are connected to 
IC3 inputs A, B, C and D. To program the 
display, set the desired BCD value at the 
BCD inputs, select the desired digit with 
address lines AO to A3, and bring the clock 
input to the low state for a minimum of 200 
ns. The first digit is selected by setting a 
binary at the address input; digit number 4 
is selected by setting a binary 3 at the 
address input, etc. 



Any 7 segment common cathode LED 
may be used with this display. MAN 4 or DL 
704 LEDs work well, wired up using the 
display card of figure 5. The use of the 
peripheral interface gates means that a single 
5 volt power supply will be adequate with- 
out any extra LED driver circuitry. The 
entire display (either one) will draw 300 to 
400 mA. 

The 8 digit multiplexed display may 



Figure 5a: Printed circuit pattern (foil side) of an 8 digit 7 segment LED assembly used with the display 
circuits. 




126 







WE DO IT WITH MIRRORS! 

(and some very sophisticated state-of-the-art memory design) 



You've probably imagined that someday you'd like to own a 
computer system with a full complement of memory: 

65,536 BYTES 

Your dream can be a reality with the Prime Radix Corporation's 

«54Ktm memory system at a very cost-effective price. And 

ecause it is a standalone memory system, you've got the 

advantage of greater flexibility not ordinarily available from 

add-in memory. Some of the features are: 

• The 64Ktm is fully buffered, presenting one TTL load to the 
memory bus. 

• The 64Ktm is digital group bus and ALTAIRtm bus 
compatible. When ordering, you must specify the bus 
architecture. A plugcard and cable will be furnished for the 
particular bus architecture you specify. 

• The minimum complement of memory is 40K BYTES, with 
starting address locations at OK, 8K, 16K, or 24K. 

PRIME RADIX • P O Box 1 1 245 • Denver 



• The 64Ktm comes assembled and tested with its own power 
supply, attractively housed in an aluminum cabinet, ready to 
plug into your system. 

• Psuedo-static operation: on board refresh clock-generator 
provides processor independent refresh with no wait states. 
The 300NS worst case access time enhances high speed 
operation. 

• Power/fail detection circuitry and battery backup will 

provide non-volatile memory (batteries are optional at extra 

cost). 

LIST PRICE IS AS FOLLOWS: 

40K 48K 56K 

$1490.00 $1580.00 $1670.00 

We are offering a special introductory ten percent discount off 
list price on all orders received on or before February 28, 1977. 
Delivery will be made in the same sequence as orders are 
received. Please allow 3 to 6 weeks for delivery. Mastercharge 
and BankAmericard are accepted. 
Colorado 8021 1 • (303) 433-5630 or 573-5942 



64K 
$1750.00 



PRIME RADIX 

COMPUTER SYNTHESIS 



City 



Print Name 



Address 



State 



Zip 



□ DIGITAL GROUP BUS 

□ ALTAIRtm BUS 

□ 64K @ $1750.00 

□ 56K @ $1670.00 

□ 48K (5) $1580.00 
D 40K @ $1490.00 



Make checks or money orders payable to: 

PRIME RADIX, INC. 
P.O. Box 11245 
Denver. Colorado 80211 
(303) 433-5630 or 573-5942 



Credit Card Number 



□ Check or M.O. enclosed 

□ Charge BAC 
D Charge MC 

{Please No C.O.D.'s or P.O.'s) 



4 Numbers Above Name (MC)Good Thru 



Signature 






127 






Figure 4b: Printed circuit component side map of the 16 digit display. See figure 2 for identification of 
components, jumper wires are shown as dotted lines in the overlay. 



CLOCK ADDRESS DATA 

+ 5V IN/ ^ -s/ r-rr^ 

Al A3 A2A0 Dl DO D3 D2 




X5 (TYPICAL DIGIT 
DRIVE OUTPUT) 



edcbagf 

SEG. DRIVE 
OUTPUTS TO 
DISPLAY BOARD(S) 



easily be used to replace the binary lights on 
a computer as an octal display. This display 
board is also a handy readout for any 
number of homebrewed instruments. 

The programmable display may be used 
as a computer output. Connect the address 
and data inputs of the board to the 8 bits of 



an output port. Connect the clock pulse 
input to the computer's output strobe line. 
Remember to program the computer to 
include the correct digit address in each data 
output. For use with hexadecimal data, use a 
substitute for the 7448 which decodes hexa- 
decimal 7 segment patterns." 



Figure 5b: Printed circuit component side map of the display matrix. The LED parts are MAN 4 or 
DL 704 seven segment displays or their equivalents. 



DIGIT DRIVE TERMINAL 



SEG. 

DRIVE 

INPUTS 



VJT 




Ty 




v-/- 




\_r 




V^r 




■xy 




■vjr 




W 


L 
E 
D 




L 
E 
D 




L 
E 
D 




L 
E 
D 




L 

E 
D 




L 
E 
D 




L 
E 
D 




L 
E 

D 



o SEG. 
b DRIVE (TO 
3 e NEXT BOARD) 



128 



Continued from page 1 21 



k recommend that a short program be written 
to cycle the cassette output between a one 
and zero every few seconds. Connect a 
frequency counter to the output and 
readjust the mark and space pots to the 
correct specifications. I also noticed that 
variations in power supply voltages from one 
time to the next can adversely shift this 
frequency. Having an adequate well designed 
power supply will limit variabilities even as 
more memory is added. My 10 K system 
draws approximately 4.4 A at 5 V and with 
1 8 K on it; it now takes 5.7 A. 

The last comment is no Digital Group 
problem, but rather mine. I assembled the 
10 K memory board as instructed, plugged it 
into the system and ran the DGS memory 
test program for a couple of hours. It all 
checked out fine, but when I tried to read 
any program which occupied 10 K of 
memory (2 K worked fine) it bombed out. 
Since the memory test program said the 
memory was fine, I was led to suspect the 
10 K BASIC tape. I shipped that tape off to 
a friend to try it on his DG system and 
contacted the Digital Group software people 
for a new tape. Within five days I had both a 
new tape from DG and confirmation from 

1 my friend that I had a problem because the 
tape was OK. But the memory test said the 
memory was OK! Well, don't believe it! In 
the process of removing and checking each 
2102 on my 8008 system I found an IC with 
a pin bent under it. Straightening this pin 
and reinserting the 2102 was all that was 
needed, and the Tiny BASIC read and 
executed perfectly. Be careful of memory 
test programs. 

In conclusion, my experiences with the 
Digital Group 8080A System have been 
gratifying. My system worked with no major 
problems, and any intelligent user either 
constructing the computer in whole or part 
should expect the same. The fact that I now 
have an operational microcomputer has 
caused a slight problem, though. I never get 
to use it! I seem to continually have people 
from my office over in the evenings pro- 
gramming one thing or another. In fact, I 
had to add another 8 K this week to allow 
more Tiny BASIC programming space for 
one guy who is writing a statistical program 
which he hopes will help him win at jai-alai. 
I suggest that if you get one of these small 
computers, just walk around with a pleasant 

* pregnant smile, but for heaven's sake don't 
tell anyone that it really works!" 

[Watch for Steve's humorous account of 
jai-alai in April's B YTE.J 



$795 



ECONOMY 

TERMINALS ANNOUNCES: 

AN INTRODUCTORY OFFER 
ON THE ET1 CRT TERMINAL 

24 x 80 display of the 64 uppercase ASCII characters 

12" Industrial 15 Mhz monitor with anti-glaire screen and filter 

- 90-day warranty (parts and labor, F.O.B. factory) 

96-hour elevated-temperature operating test on each ET1 before 
shipping 

RS-232 and 20 ma interface 

LF, CR, BS, Local, Rubout. Break, Home Clear, Tab*, Remote Cursor 
Placement*, and Scroll* functions with special function keys 

Sixteen switchable baud rates to 19,200 

Odd, even and mark parity with one or two stop bits 

Micro-Processor Based, with 63-key keyboard 

'These functions vary with model selected. 

PLEASE CALL OR WRITE FOR MORE INFORMATION. 

THIS OFFER EXPIRES 30 APRIL, 1977. 



ECONOMY 
TERMINALS 



Box 12261 

Minneapolis, Minn. 55412 

(612) 522-1076 



MORE POWER TO 
YOURALTAIR* 

12 AMPS @ 8v. (nominal) 
2 AMPS® ±16v. 



At any line voltage from: 

90 to 140 volts. 

Installs easily inside any A I tair* 8800 or 
8800a. 

Over voltage and over current protected. 
Conservatively designed and specified. 



only $90.00 

postpaid in the U.S.A. 
California residents add 



master charge 



$5.40 sales tax. 




PARASITIC ENGINEERING 



PO BOX 6314 



ALBANY CA 94706 



* Altalr is a trademark of MITS Inc. 



129 



Another 



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130 






PAPERBYTES ™ 
Test 



As noted in last month's BYTE, page 1 21 , 
we had intended to have an extended text 
included in the magazine for February. The 
text got delayed, due to a combination of 
human, weather and Murphy's Law Factors. 
This month, it arrives at the printing presses 
for publication. 

This text is an extended set of ASCII 
encoded English language words. The bit 
level format is format 3 (compressed ratio 
recording) as described in previous articles 
on the subject in BYTE November 1976, 
page 10, and BYTE December 1976, page 
12. In this format, the width of the bars and 
spaces are encoded as follows: space = 1 unit 
width; zero bit = 1 unit width bar; one bit = 
2 unit width bar. The frame format begins 
with an ASCII SYN (10010110) character 
extended to 8 bits with a high order 1 bit. 
The frame continues with 8 bits of check 
sum, 8 bits of line identification, and 8 bits 
of byte count. The byte count sets the 
number of data bytes which follow the 
header. 

Add Some Zest by Making a Contest 

Rather than just print another test, we 
decided to make this text sufficiently 
complex to warrant making a small contest 
out of it. Within the frame format wc have 
encoded the plain text of ASCII upper and 
lower case characters (plus line control) 
defining Walter Banks' parody of a famous 
poem dealing with mythical critters and 
strife and conquests. Lewis Carroll purists 
will object to the arbitrary and incompre- 
hensible semantic transformations made on 
the arbitrary and incomprehensible seman- 
tics of the original, but the necessities of 
making a contest required uniqueness: This 
version has never been published before and 
it is completely different at the detail level. 
All contests have ground rules, and here are 
the ones which apply to the first (and 
probably only) PAPERBYTES Contest: 

• Entries must be received in our office 
by March 31 1977. They should be 
addressed: 

BYTE magazine 

Attention: PAPERBYTES Contest 

70 Main St 

Peterborough NH 03458 



ACT-I 



MICRO-TERM INC. 




$525 complete with high resolution 9" monitor • $400 without 
monitor INCLUDED FEATURES: 



• Underline Cursor 

• RS232C or Current Loop 

• All oscillators (horiz., vert., 
baud rate, and dot size) are 
crystal controlled 



64 characters by 16 lines 
Auto Scrolling 

Data Rates of 110, 300, 600, 
1200, 2400, 4800, and 9600 
baud are jumper selectable 



The ACT-I is a complete teletype replacement compatible with 
any processor which supports a serial I/O port. Completely 
assembled and dynamically tested. 
Prices FOB St. Louis Mastercharge and BankAmericard 



THE AFFORDABLE CRT TERMINAL 



MICRO-TERM INC. P.O. BOX 9387 ST. LOUIS, MO. 63117 
(314) 645-3656 



MULLEN COMPUTER R QARn<S 



BOX 6214 ■ HAYWARD, CA. 94545 




N AL¥ AIR/IMIAI 

E 



& 



NEW FOR TROUBLESHOOTING' 
AND DEVELOPMENT: A SUPER 
EXTENDER BOARD FOR THE -* 
S-lOO BUSS. V 

• Built in, 3 LED TTL logic probe A 

• Jumper links in power lines for easy 

B current measurement and fusing a 

• Edge connector label identifies all pins 
Outstanding instructions fj 

Full width card; gold connector teeth 

^AT YOUR LOCAL COMPUTER r 
STORES, OR ORDER BY MAIL. [ 



O: 



CAVE 



R D MI: $3§ 



131 






Personal Computing 
Goes National 

It's happening at the Dallas Convention Center 
during the 1977 NCC, June 13-16 



** 



* 



* 


it 


* 


w 


* 


• 


* 


it 


k 



The 1977 National Computer Conference will be the year's largest gathering of 
data processing users, computer professionals and computer Hobbyists. More 
than 25,000 people are expected to gather in Dallas for a conference program 
of more than 100 sessions and the year's largest display of computer hardware, 
software, systems and services — plus the first annual National Programming 
Contest and a series of outstanding Professional Seminars. 

Specially featured will be the first NCC Personal Computing Fair & Expostion, 
comprising a Personal Computing Fair, papers and panels, club congress, head- 
quarters hotel and product exhibits by leading manufacturers. 

Entry Deadline Coming Fast 

Personal Computing Fair entries must be non-commercial personal or group- 
owned small computing systems. They may feature hardware and/or software 
implementations, games, recreation, music, art, amateur radio, scientific, miscel- 
laneous and general applications. Prizes and awards will be given in all categories. 

Working systems are desired, although projects that might not lend themselves 
to display at the fair might be illustrated audio/visually if the judges believe the 
project is acceptable otherwise. NCC will provide at no charge the booth space, 
a sign, coordinated furnishings, power and lighting. Accepted entrants will earn 
free full conference registration (except for the Proceedings). 

For information, write or call Ric Martin, Personal Computing Fair chairman, c/o 
The Micro Store, 634 S. Central Xwy., Richardson, Tx. 75080, 214/231-1096. 
To enter, send him a concise, one-page, double-spaced description of your sys- 
tem, with your name and home and business addresses and telephone numbers. 

Entry Deadline Is March 1 5 
Acceptance Announced By April 15 




1977 NATIONAL COMPUTER CONFERENCE 

Dallas Convention Center • June 13-16 



• Each entry should contain a stamped 
self addressed envelope (as well as 
redundant identification of the con- 
testant) in the event materials are not 
used by our office in the publication. 

• Each entry must contain the com- 
pletely decoded text, either as a 
printed text listing (upper and lower 
case) or as a hexadecimal absolute data 
listing with one line per line of bars. 
Handtyped listings are fine, if you 
don't have a hard copy device. 

• Each entry must be accompanied by 
a complete and detailed technical 
description of the system used to 
decode the text. Hand decoding is not 
an acceptable method. Brownie points 
in the judgment of entries will go to 
the least expensive systems (other 
things being equal). 

While it is not necessary to treat entries as a 
formal technical article submission, winners 
and runnersup in the competition may be 
published with payment at our current rate 
for highly desired technical materials. 

The Prize? 

A check for $100 will be the bonus for 
the winning entry in this contest, as judged 
by BYTE's editor Carl Helmers based upon 
materials submitted. 

A Note About Formats, 

Coming PAPERBYTES Items, etc. 

In this sample text, we do not provide the 
equivalent human readable form of mate- 
rials. This is due to the nature of this 
month's test which is being treated as a 
contest. The arrow identifies the beginning 
of the text. 

Normal practice when publishing pro- 
grams in BYTE is expected to include 
printing of a complete hexadecimal object 
text for programs as a confirmation of the 
bar coded machine readable texts. Produc- 
tion problems notwithstanding, the first 
program we expect to print in this form will 
appear as bar codes in the May 1977 BYTE 
in the second part of Jack Emmerichs' 
article on his "Tiny Assembler" for the 
Motorola 6800. We've been using Jack's 
assembler (we = Walter Banks at the 
University of Waterloo, Carl Helmers at 
BYTE, Chuck Adams at Texas A&M 
University) since late in 1976. Also planned 
for future release in this form are additional 



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133 






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systems software programs for the popular 
processors. 

What About Source Code? 

When publishing object code for extended 
programs, such as Jack's assembler, or a 
BASIC interpreter or other software, the 
length of the source listings preclude 
reproduction in the magazine. The source 
code of the Tiny Assembler runs 40 pages 
for example. To provide the source code for 
those individuals seriously interested in 
modification and extension of programs of 
this form, PAPERBYTES will be making 
available extended documentation for pro- 
grams including users manual information, 
source listings, a reprint of any BYTE 
articles discussing the programs, and addi- 
tional documentation depending upon the 
type of program being published. The 
PAPERBYTES release of Jack Emmerichs' 
assembler user's manual is in preparation 
coincident with preparation of his articles 
for publication." 



Attention, Engineers of Bar Code Readers: 

On page 320 of the November 20 1976 
issue of EDN magazine, there is a short note 
•sent in by Wesley Grenlund of Beloit 
Corporation, Rocton IL, concerning a signal 
processing circuit for scanners. The circuit 
combines a Texas Instruments Tl LI 39 
source-receiver assembly with the 75140 line 
receiver to make a TTL level input to the 
single bit port needed by bar code scanning 
software. The only additional part probably 
needed is some slit optics (.01 inch [.0254 
cm] wide for our bars) to define a limited 
active area. The slit would be positioned in 
front of the intersection point of the source 
beam and the receiver viewing path, as 
suggested by Dave LeVine. 

We received a similar hint to use the 
Tl L1 39 in early October from Dave (who is 
chief engineer of Computer Link, Burlington 
MA). Dave says he has successfully used the 
Tl LI 39 together with a single National 
Semiconductor 74C14 hex Schmitt Trigger 
integrated circuit as the sole input processing 
amplifier: This version uses one of the 
Schmitt triggers in the package as a 
capacitively coupled amplifier (open loop 
and saturating), with the remaining five 
triggers ganged in parallel to drive a TTL 
unit load from the output of the first trigger. 
This hint popped out of Dave in the context 
of the usual "micro session" (would be 
called "bull sessions" in any other field) 
which occurred at the October 1 976 meeting 
of the New England Computer Society." 



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PS-1 Power Supply Kit. Provides plus and minus 16 volts required for 
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135 









BYTE BINDERS and FILES 



BYTE's Bits 



Preserve those precious first 16 issues 

with either a handsome but rugged 
library file— or a binder— in flag blue 
Kivar library fabric stamped in gold 
leaf. 




®i 




Files: Made to hold the first 1 6 issues of BYTE. Price per 
file $4.95 ; three for $ 1 4 ; six for $24, postpaid. 

Binders: Made to hold the first 16 issues of BYTE. Price per 
binder $6.50; three for $18.75; six for $36, postpaid. 

(Add $1 each outside USA.) 



Send to: BYTE, POB 5120, Philadelphia PA 19141 

I enclose check or money order for $ 

Please send me BYTE _F'' es Binders 

Name 



^please print) 



Address m 
City 



State 



_Zi P . 



Satisfaction guaranteed or money refunded. Allow at least four 
weeks for delivery. 



Guinness, Take Note: 

The World's First Commercial 
Personal Computing System 
Product to Use 1 6 K Dynamic 
Programmable Memory Chips . . . 

A recent phone call from Steve Jobs 
(who, with Steve Wozniac, is responsible 
for the Apple Computer Company) re- 
ported what is claimed to be the first 
shipment of a personal computer sys- 
tems product built with the new 16 K 
dynamic memory chip products. The 
product which used these chips was an 
Apple I - an MOS Technology 6502 
proccessor board with 32 K 8 bit bytes 
of memory (16 chips), read only 
memory systems software, and video 
interface. The board was delivered to 
one of the Byte Shops in the San 
Francisco Bay area on December 17 
1976, for sale to a retail customer. 

Larger and larger amounts of 
memory will be the trend in small 
computer systems for some time, due to 
the combined factors of its immense 
desirability as a programming resource 
and the dropping prices of ihe new LSI 
semiconductor technology. The use of 
the 16 K chips in Apple was made 
possible by the fact that the manu- 
facturer of these memory parts chose to 
make the 16 K designs essentially pin 
compatible with their older 4 K designs 
by using a change in the logical interpre- 
tation of one of the lesser used pins of 
the package. This pin now serves as the 
seventh address bit in each of the two 7 
bit address segments which form the 14 
bil address needed for a 16 K bit array. 
The Apple product demonstrates the 
success of this idea since it will take any 
combination of 4 K and 16 K chips in 
byte wide groups. Watch very shortly for 
advertisements of the new Apple II 
computer, both as a finished product 
and as a board level computer which 
looks like it will be an excellent and 
innovative addition to the marketplace." 

A HAM Swapfest 

The 7th Annual North Florida Swap- 
fest sponsored by the Playground Ama- 
teur Radio Club (PARC) will be held in 
Fort Walton Beach FL at the Okaloosa 
County Shrine Fairgrounds on Saturday, 
March 19 and Sunday, March 20 1977. 
The Swapfest will be a full weekend 
affair with the display area open from 
8:00 AM to 4:00 PM each day. A dinner, 
featuring a prominent speaker, will be 
held at the Fort Walton Beach Holiday 
Inn Saturday evening. The North Florida 
Swapfest is an annual event, sanctioned 
by the American Radio Relay League 
(ARRL), and draws hundreds of Radio 
Amateurs and electronics experimenters 
primarily from Louisiana, Mississippi, 
Alabama, Georgia, and Florida, although 



136 






amateurs from many other states attend. 
The North Florida Swapfest is a 
nonprofit function and proceeds are 
used to finance local Amateur Radio 
projects, the next year's Swapfest and 
the Playground Amateur Radio Club 
Scholarship Fund. Interested in informa- 
tion on booths or attendance? Contact 
Bill Callanan WB4FTA, Swapfest Chair- 
man, Playground Amateur Radio Club, 
POB 433, Fort Walton Beach FL 
32548." 

A Mention 

MICROCOMP is a new computer 
store, dealer of OSI products, located at 
785 S Main St, Fond du Lac Wl 54935. 
Phone (414) 922-2515, or write Nyles 
Priest of MICROCOMP." 



BYTE's Eisgs 



Why the DACs "Don't Work" 

Author Steve Ciarcia sent our way 
(via his friend Chris Morgan who stopped 
by one recent Saturday) the following 
correction to his article "Make Your 
Next Peripheral a Real Eye Opener" on 
page 78 of November 1976 BYTE. In 
the schematic of pages 84 and 85 (fig- 
ure 2), we (Steve or CH at BYTE? Who 
knows?) omitted notation of the nega- 
tive supply pin for the MC1408-L8 
digital to analog converters, IC4 and IC5. 
Pin 3 of each 1408 should be wired to 
the —15 V supply." 

Weathering the Storm 

Author Mike Firth, whose article "Do ft 
Yourself Weather Predictions" appeared 
on page 62 of December J 976 BYTE, 
sends in the following items: 

In my article on the weather, a call 
from Tom Harper in Miami FL has put 
me on the track of two problems, which 
I describe below: 

On page 66 (BYTE December 76), 
the simple formula for relative humidity 
(H = 100% - T*5) is said to be for centi- 
grade temperatures, but in fact it is for 
Fahrenheit, an error caused by an error 
in my original source. To use the equa- 
tion for centigrade temperatures, the 5 
should be changed to an 8. 

In using the more complex formula, 
three different values of E, the vapor 
pressure, must be used, but my article 
made it seem that only two were needed. 
Two are obtained from a table or by 
interpolation from the values given at 
the top of page 66. They are E w , the 
vapor pressure of water at the wet bulb 
temperature, and Ej, the vapor pressure 
of water at the dry bulb temperature. 
The third value is E, the actual vapor 
pressure in the air from the formula. The 
proper formula for relative humidity is 
then: 

RH = E/Ed (not RH = E/E w as given 
in the article)." 



SCFTKIflRE 






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ATOR. THE PACKAGE CONTAINS NELL COMMENTED AS- 
SEMBLED SOURCE LISTINGS, SORTED SYMBOL TABLE. 
HEX DUMP, INSTRUCTIONS AND SAMPLE OUTPUT, ALL 
IN AN ATTRACTIVE BINDER. NO TAPES AVAILABLE 
AT THIS TIME. ORDER PD80-1 $19.95 

6502 PACKAGE 

A PACKAGE IDENTICAL TO THE ABOVE IS AVAILABLE 
FOR 6502 BASED SYSTEMS. THESE PROGRAMS ARE 
JUST NHAT YOU NEED. PD65-1 $19.95 

PROGRAM OF THE MONTH CLUB 

PROGRAM OF THE MONTH CLUB IS A UNIQUE SERVICE 
AVAILABLE TO THE HOBBYIST. FOR $2.00 YOU NILL 
RECEIVE A 1 YEAR MEMBERSHIP NHICH INCLUDES A 
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ORDERING INFORMATION 

PLEASE INCLUDE 3 7. POSTAGE, INDIANA RESIDENTS 

ADD 4V. TAX (US FUNDS ONLY). CHECK YOUR LOCAL 

DEALER FOR OUR PRODUCTS. (DEALER INQUIRIES 

WELCOMED). SEND $.25 FOR A COMPLETE CATALOG. 



TSC 



TECHNICAL SYSTEMS CONSULTANTS 

BOX 257t H. LAFAYETTE INDIANA 47908 



TSC 



Computer 
System Engineers 

Computer Transceiver Systems, Inc., manufacturer of portable 
computer terminals, is expanding its R&D facilities. New de- 
velopmental programs getting under way are specifically di- 
rected towards state-of-the-art applications of microprocessors 
and allied LSl.components into the CTSI product line. Positions 
are open in several areas for knowledgeable, enthusiastic indi- 
viduals who would like to join a small dynamic company and 
tackle challenging and rewarding projects. 

MICROPROCESSOR SYSTEM ENGINEER 

Qualified individual shall have a minimum o f 10 years o f design 
experience including 1-2 years of system design and implemen- 
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essential. Ability to develop electro-mechanical interfaces 
desirable. 

Designer shall also be capable of developing test equipment for 
use by manufacturing and field service. 

SENIOR ELECTRONIC ENGINEER 

Innovative engineer with a minimum of 5 years of experience 
with high-speed logic systems, and with hands-on experience 
with microprocessors. Must be familiar with TTL, MSI, and LSI 
components. Experience with power supply and analog circuit 
design desirable but not essential. 

SENIOR LAB TECHNICIAN 

Qualified applicant shall have a minimum of 5 years of experi- 
ence assembling and testing prototype electronic systems. 
Must be familiar with the use of laboratory test equipment and 
must be capable of layout and breadboard assembly from sche- 
matics. Should be familiar with digital logic. 



Send resumes to the attention of Mrs. Diane Palmer, Computer 
Transceiver Systems, Inc., P.O. Box 15, Paramus, N.J. 07652. 






137 



How To Make Your Computer 
Even More Boring . . . 




interface it with a Midwest Scientific Instruments FD-8 
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With our FD-8 system and FDOS firmware, your com- 
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routines on PROMS, all you have to do is load your desired 
program from disk and start running. Of course you may 
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load if you have lots of memory. 



The FD-8 interfaces to any micro- 
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and all of our available software is 
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MSI FDOS operating system software 
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• Automatic program loading and linkage 

• Auto error recovery 

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• Utilities for file listing, copying, 
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The FD-8 is 
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Prices: 

FD-8 Floppy Disk System 

Kit $1,150.00 

FD-8 System Wired 

and Tested $1,395.00 

PROM/RAM Kit (SwTPC 

6800 or 8080) $95.00 

PROM/RAM Wired & Tested, 

with FDOS Firmware (specify 

6800 or 8800 System) $345.00 

PR-1 Programmer & 
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Designed to program 1702A PROMS, 
the MSI PR-1 interfaces with any 
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A complete software package is 
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the software reads the PROM back 
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The PR-1 is complete, including 
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PR-1 $325.00 



Send for New 
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220 West Cedar 

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913/764-3273 

TWX 910 749 6403 (MSI OLAT) 



Here are two MSI Dealers who can show 
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MSI is a dealer for Southwest Technical Products • Mastercharge & Bank Americard Orders Accepted 



HOUSTON now has a full service 
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following manufacturers. 



• IMSAI • LEAR SIEGLER 

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• TDL • ICOM 



For your professional application 
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Pictured above is the new OP-80A 
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watt carbon film resistors $0.03 

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10 percent, 50 per value min. 

No-Nik wire strippers 516.00 

10,12,14,16,18,21,23,25,28,31 
34,37,44 or 54 thousanths 
wire diameter 

Carbide PC board drills 



wire size: 


55 


65 


$2.88 




66 


70 


$2.97 




71 


75 


$3.06 




76 


78 


$3.60 




79 


80 


$3.60 



Spec sheets are available. 

We would be pleased to send you a 
'GOODIES' catalog listing all kinds of 
hard to find products including : Molex, 
Bishop Graphics, AMP, CDC manuals 
and forms, PC drills and mills, elec- 
tronics tools, PC board manufacturing 
supplies, resistors, and semicon 
ductors. 



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PROGRAMMING 

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with microcomputers. Presented 
in a modular sequence of 10 
lessons oriented for the new 
programmer. Extensive reference 
material you will use long after 
you become an accomplished 
microcomputer software designer. 
Much of the information in the 
course has been available only 
through costly seminars. Now 
you can purchase this complete 
home study course for under 
$50.00. Send for free descriptive 
brochure now. 

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SERVICES INCORPORATED 

711 Stierlin Rd, Mountain View, 
C A 94043 (415) 965-8365 



I 



mmm 



Classified Ads 



FOR SALE: ASR-33 TTY with adjustment and 
parts manuals. Very good condition, $700. With 
acoustic coupler, $750. Donald Bailey, 19 Shaker 
Rd, Concord NH 03301 , (603) 224-0486. 

FOR SALE: Two MITS 88-MCD 4K dynamic 
memory cards for Altair 8800, assembled, com- 
pletely tested, meet specs for use with disk, $200 
each, including edge connector. Vintage BYTEs, 
issues 1 through 4, $5 each. David Richards, 6655 
Hill St, El Cerrito CA 94530, (415)529-0759, 
evenings. 

FOR SALE: Attention computer hams: Morse to 
ASCII decoder. All controls accessible from front 
panel. Work with TVT 1 or TVT 2. I have helpful 
documentation on the decoder that I will pass 
along on request for $1.50 to handle cost of photo 
copies and postage. Asking $75 for the unit. Write 
Jack S Davis, POB 5, Endwell NY 13760, 
(607) 754-0309. 

FOR SALE: E and L Instruments MMD-1 8080A 
based microcomputer complete with keyboard, 
256 bytes RAM, 256 bytes of PROM programmed 
for keyboard entry and execution of programs, 
power supply, interfacing and breadboarding 
socket, case, and 40 pin edge connector for 
expansion. Includes modular, self-taught, micro- 
processor course. Assembled, tested, excellent con- 
dition, $300. Richard Criscuolo, 303 Oak Av, 
Lindenhurst NY 11757, (516) 884-3882. 

SWAP OR SELL: SWTP CT-1024 TVT 2 with 
serial IO, manual cursor, screen read, P/S. Two 
Altair 8080 CPU boards, Tarbell interface, HAL 
ST-6 Teletype converter with all options (can be 
used as a modem). All in like new condition and 
guaranteed perfect. Need hard copy printer or ??? 
Michael Shrayer, 930 S Bonnie Brae St, #331, Los 
Angeles CA 90006, (213) 380-6509 

FOR SALE OR SWAP: Texas Instruments SR-52 
card programmable calculator, complete with all 
standard accessories and manuals. It has a special 
programming manual with many programming 
tricks, procedures for accessing 60 data memories, 
and procedures for reading and writing data onto 
cards, $200 or fair trade for S100 bus, Altair- 
IMSA1, compatible memory or IO. R W Toy, 
155-A Duncan, San Francisco CA 94110, 
(415) 648-6105. 

WANTED: November 1975 issue of BYTE. Will 
consider purchase or trade for this issue only, or 
possibly, for a set of issues. Chris Bauer, IEMS 
Dept, Florida Technological University, POB 
25000, Orlando FL 32816, (305) 275-2236. 

FOR SALE: Friden Flexowriter Baudot Teletype 
with five level paper tape punch/reader plus card 
reader. Can be converted to ASCII, $95. Derek 
Hendry, 64 The Uplands, Berkeley CA 94705, 
(41 5) 654-5583. 



Readers who have equipment, software or other 
items to buy, sell or swap should send in a clearly 
typed notice to that effect. To be considered for 
publication, an advertisement should be clearly 
noncommercial, typed double spaced on plain 
white paper, and include complete name and 
address information. These notices are free of 
charge and will be prin ted one time only on a space 
available basis. Insertions should be limited to 100 
words or less. Notices can be accepted from 
individuals or bona fide computer users clubs only. 
We can engage in no correspondence on these and 
your confirmation of placement is appearance in 
an issue of BYTE. 

Please note that it may take three or four 
months for an ad to appear in the magazine. ■ 



WANTED: Software and hardware schematics for 
music synthesizers (computer controlled or not). I 
am especially interested in automated music com- 
position. Bill Struve, 505 Meade Cir, Memphis TN 
38122. 

WANTED: SCCS Interface issues December 75, 
February 76 and March 76. Please let me know if 
you have them for sale. Thomas R Baley, 279 
Gehring Rd, Tolland CT 06084. (203) 872-7084. 

FOR SALE: Mostek F-8 evaluator kit fully assem- 
bled and working with literature. Two complete 
Viatron 2100 systems working with the complete 
literature pack. The first check (certified) or M O 
for $900 takes all. Donald E Scherck, Rt One, 
Collbran CO 81 624. 

SITUATION WANTED: Research physicist, with 
several years practical digital design experience, 
breadboarding, prototyping, etc; thorough reading 
knowledge of microprocessors and software. Look- 
ing for position with computer store, computer 
consultants or similar, in which my abilities can be 
traded for salary and chance to learn micros. Jay 
Kirschenbaum, 350 E 30th St, Apt 4L, New York 
NY 10016, (212) 684-5525. 

NEED: BYTE issues 1, 2, 3, 8, 9 and 10. Willing to 
swap money for them, but have surplus copies of 
other issues of BYTE as well as assorted test 
equipment and digital hardware and components. 
How about a handful of 2102s? Hank Irvin, Dept 
of Physics, Tulane University, New Orleans LA 
70118. 

WANTED: I will buy your new, used, or dead 
Altair 8800, working or not, for cash. I am 
desperate for Altair. Help out a poor college kid. I 
will also trade for your machine. I have a scope and 
a Teletype. Call anytime. Jim Webb, POB 5224, 
Carson CA 90749, (213) 325-4684. 

FOR SALE OR TRADE: PDP-8 mini-computer 
(straight-8), mounted in attractive walnut cabinet 
(spouse-approved for den). Complete with mainte- 
nance manual, drawings, 4 K BASIC, 4 K FOCAL, 
editor, PAL III assembler, disassembler, TTY inter- 
face, games, etc. Perfect condition. Free DECUS 
membership available for additional software. Pres- 
ently in use with ASR model 33 Teletype. Can be 
sold with or without model 33. Sale price W/O 
Teletype $800. Rex Engle or Jim Speidel, POB 
10498, Charlotte NC 28288. (704) 374-6409. 

TERMINALS: BURROUGHS 9350-2, ASCII, 
15cps upper and lower case, $200. Friden Flexo- 
writer, model SPS with paper tape reader and 
punch, $200. Univac DCT500, 30 cps printer, no 
power supply or interface, $100. Phil Hughes, POB 
2847, OlympiaWA 98507. 

FOR SALE: Altair 8800 system with 8 K RAM, 
88-SIOA, 88-ACR, 8K BASIC, assembled and 
running, $1167. SWTP CT-1024 complete, unas- 
sembled, less monitor and case, $275. Friden 
ASCII communications terminal from Herbach and 
Rademan with control unit, $200. Chris Foreman, 
POB 127, Reseda CA 91335, (213) 342-8845. 

WANTED: BYTE issues for October and 
November 1975; April, May and June 1976. Please 
notify the following indicating price desired: Tech- 
nical Library, Bell Telephone Laboratories, 
Western Electric Co, 2525 Shadeland Av, Indian- 
apolis. IN 46206. 

FOR SALE: Cryptographic program that will 
baffle the codebreakers of the CIA. Encode and/or 
decode your private correspondence for maximum 
security. Documentation of cypher technique, pro- 
gram listing and punch paper tape in BASIC for 
only $6. Jon Stedman, 1528 Summit Rd, Berkeley 
CA 94708. 

FOR SALE: Pacer: a 16 bit micro with TTY 
interface, line assembler in ROM and complete 
documentation. .Assembled and running in cabinet 
with 32 key control assembly. Call (213) 243-5179 
or write POB 430, Glendale CA 91206. 

WANTED: Back issues of BYTE. Desire 1 copy 
each of issues 1 through 14. Will pay $3 for each 
complete issue in good condition. Call 
(313) 323-3574 or write R Parenteau, 11020 Bur- 
lington ?409, Southgate Ml 48195. 



WANTED: Back issues of BYTE magazine: issues 
2, 3, and 8. Please send price and condition 
information to Art Leyenberger, 142 Kenilworth 
Rd, Ridgewood NJ 07450. 

WANTED: BYTE magazine issues 7, 8. 9 and 10 in 
good condition only. Frank E Marfai, 2839 Her- 
mosa Av, La Crescenta CA 91 214. 

FOR SALE: Brand New ASR-33 Teletype with 
auto reader. I reconfigured in midstream and will 
sell this superb $1,188 value for only $950. 
Immediate delivery instead of usual 4 to 6 month 
wait. J Katz, 1921 Pelham Av, Los Angeles CA 
90025.(213)474-3347. 

FOR SALE: Altair 8800 computer, well built and 
checked out, $500. Two MITS 4 K RAM boards, 
$150 each. One PTech 4 K RAM board, kit 
untouched, $120. One 4 K X 8 EPROM board with 
assembled monitor, $150. One MITS RS/232 S10 
board, $100. SWTPC TVT 2 with 510 and PS and 
keyboard and monitor, $300. SWTPC cassette 
interface well built unchecked, $70. 32RO TTY 
new, $300. Best offer takes any or all. Louis 
Doctor, BARH D311, RPI, Troy NY 12181, (518) 
270-7586. 

CHANGING HOBBIES: Want to swap miscella- 
neous ham gear for computer and/or peripherals. 
Have Heath SB-303 with optional crystal filter and 
other items too varied to list. Also have near new 
Heath stereo mike mixer and miscellaneous test 
equipment, all in good condition. Also willing to 
swap professional (First Class Federal License) 
assembly service or technical assistance for devices. 
Call or write Mike Hales, Route 1, POB 30W , San 
Juan TX 78589, (512) 383-7233. 

WANTED: Manual or schematics and timing infor- 
mation for IO circuits of IBM model 72 Selectric 
typewriter/terminal. CG Bothner, POB 153, Land- 
ing NJ 07850. 

FOR SALE: Tektronix model 611 graphics storage 
display scope, $450. Also have Tektronix model 
581 oscilloscope with type 82 plug in and scope 
mobile, $400. Will trade for Altair 8080. Don 
Heinlein, 1546 E 215th PI, Carson CA 90745, 
(213) 830^*225. 

FOR SALE: Altair 8800a, 16 slot memory board, 
fan; two 4K dyn, two 4K static, ( 16 K total 
memory); ACR IO; 3P+S IO; TVT II with 64 
characters per line; SCM Telewriter; software. 
$2150. Will separate. Evenings: (312)328-5610. 

FOR SALE: GE core memory 16 K by 40 bits, all 
power and interface circuitry and documentation 
— been used with an 8080 processor. Litton 
Industries drum memory with full read write 
electronics. Bryant MBM drum memory. By unit or 
best offer over $250 for lot. C H Eby, 7101 
Mammoth Av, Van Nuys CA 91405, 
(213)988-1763. 

FOR SALE: Microprocessor system by Control 
Logic. Contains three basic cards; central proc- 
essing unit using an 8008 input output control 
providing clocking and processor control signals, 
and memory address storage which provides latch- 
ing registers for memory and output data control 
and a 256 byte PROM. Also included: 1 K of 
2102 RAM, card mounting hardware, and logic 
diagrams, $100. K Talen, 10605 Double Spur 
Loop, Austin TX 78759, (512) 258-4282. 

FOR SALE: PolyMorphic VTI 64 video module, 
64 characters per line, keyboard input port, Greek 
control characters, $200. Morrow's Godbout Cas- 
sette Interface (BYTE Standard) fully expanded, 
with 3 cassette channels, parallel and RS-232 TTY 
10 ports, and operating system in EROM, $120. 
Both boards assembled and working with ICs in 
sockets, and postpaid in continental US. Shipped 
within 24 hours of receiving MO or certified check. 
Tom Burke, 150 Church St, Burlington VT 05401. 

MICRODATA REALITY: Are there any other 
computer hobbyists using this system? If so, I'd 
like to say hello, swap notes and programs, etc. 
Would also like to know where to buy a 4 or 8 way 
video terminal interface card and other peripherals 
for Microdata Reality (Model 1600 processor). 
Jack Hardman, 140 Forest Av, Glen Ridge NJ 
07028, (201)429-8880. 






140 



ST. LOUIS 



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circle reader number 140 



? CONFUSED? 

Save $100 -200 
Up to 30% Discount 

If you are like most people, you are 
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what do you actually get? HELP! ! ! 

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BITS, BYTES & PIECES 

6211 Quincewood Circle 

Citrus Heights CA 95610 

(916) 726-6469 



THE BETTER 

BUG TRAP 

The Better Bug Trap is an 
Altai r/IMSAI plug-compatible 
board that extends system capa- 
bilities to facilitate software 
debugging and real-time proces- 
sing. Capabilities include interval 
timer, real-time clock, watchdog 
timer, processor slowdown, and 
clock with variable rates. Four 
hardware breakpoint addresses 
allow you to stop processing or 
generate an interrupt at a break- 
point without modifying exist- 
ing software. The board services 
its interrupt with a CALL 
instruction to ANY memory 
address you choose. All capabili- 
ties may be set by software or 
front panel. Write for free 
literature. 

$180 assembled, tested, com- 
plete documentation, software. 

MICRONICS, INC. 

PO Box 3514 
Greenville, N.C. 27834 



7338 Baltimorr Ave . Suite 200 

College Park. Maryland 20740 

JOINT VENTURE 

GROUP OEM BUYS 

IMSAI made kits fa assembled units 15% OFF LIST 

TEC-9900-SS-UF. 16 bil TI9900 mooP, 32 bit 1/0. 
hardware mull 6 div. bullered bus. 20 ma or RS 232. 8 
nterruPts 6 sockets $259.00 



TEC-9900-32KB 32K bytes memoiy. 

TEC-9900-PPnowei supply 

SPHERE kits 6 assembled units 

SWTPCkits 6 assembled units 

CROMEMCO kits fa I 1 

SANYO TV Monitors 

TDLZPU&Z16K , 



$629.00 

$125.00 

_10% OFF LIST 
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_10%OFF LIST 
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SEALS 8k bat backup Mem 10% OFF LIST 

PERSCI Dual (loppy & intelligent controller (#270 fa 

1070) $1395.00 

SHUGART MINI FLOPPY $350.00 

AMD FACTORY PRIME TES7EO for MIL STD 883C 



91 L02 500ns _ 
91 L02 400ns _ 
Z-80 m.croP . 
Z-80CPC_ 



_$1.90 
_$1.99 
_$54.00 
_$15.00 

8080A2 5MH $17.00 

8080 PPI $10.00 

8212 I/O port $2.50 

8228 Clock Dnvur $5.50 

9555 PPI $9.50 

2708 Enrom $65.00 



_$1.85 
_$1.95 



9102 500 ns 
9102 410ns 

Z80-PI0 __ $15.00 

1702A EPROM $8.00 

8080A 3 MH $20.00 

8080SCI $10.00 

8224 Clock Gen $4.75 

8216/26 Driver $2.50 

9551 PCi $9.50 

2102 6b0 ns $1.75 



ADM-3K+ CRT & addressable cursoi $925 00 hst $825.00 
AXIOM 80 col. 160 char/sec primer, parallel interface 

$665 OOlist. serial interface $740 00 list 10% OFF LIST 

Nat. Multiplex Digital Tape recorders fa kits 10% OFF LIST 

MSI fl«p»vs fa ktts 10% OFF LIST 

Pennywhistle modem 5% OFF LIST 

Tl "sileni700" model 743. printer $1395 l.st 5% OFF LIST 
ASTRAL 2000 kits 10% OFF LIST 



Send 52 00 for newsletter & hsts 

other chips 2900 series. 4K mems etc 

16 pm socket & cap for memory chip 2b 

full payment (or discounts, add 4%. mm 4 00 

for shipping fa handling, orders bulked for 

lowest discount on OEM Group buys 

prices subiect to change without notice 



Conducted by 
Peter Travisano 



HP-65 Users Club 

The HP-65 Users Club is by, of and for 
those people around the world who use and 
enjoy Hewlett-Packard calculators. Its news- 
letter 65 Notes is a must for anyone stuck 
on these machines. Volume 3, Number 9, is 
a special games and programs issue. HP-25 
Roulette is a mathematical duplicate of the 
Monte Carlo original, complete with broken 
bank. Depending on your imagination or 
your friends' bank accounts this program 
could conceivably save airfare to Las Vegas. 
Another program for your HP-25 is Battle- 
ship II, a game which starts with random 
shooting at your opponent's hidden fleet 
until a discernible pattern appears; after 
that, it's a race to sink the enemy's ships as 
quickly as possible. Number Guesser is a 
handy way to decide all kinds of distasteful 
things like whose car do we take or who 
pays for lunch: sort of an electronic short 
straw. 

There are plenty of other games and 
ideas. So if you want to get the most out of 
your Hewlett-Packard calculator, be sure to 
send for more information from the HP-65 
Users Club in care of Richard J Nelson, 2541 
W Camden PI, Santa Ana CA 92704. 

Dayton Microcomputer Association Formed 

Looks like Dayton OH hackers are off to 
a fine start with well over 100 hobbyists 
working together to form a new club. 

Meetings take place on a regular basis, 
7:30 PM on the last Tuesday of each month. 
For more information write Dayton Micro- 
computer Association, in care of Dayton 
Museum of Natural History, 2629 Ridge Av, 
Dayton OH 45414. 

Montreal Micro 68 — Club des Mordus 
d'el Ordinateur — Computer Club 

The world's first bilingual computer club 
has been organized in Montreal. Among 
other projects, Micro 68 plans to exchange 
computers, hardware applications and soft- 
ware with other clubs in the US. For more 
information, get in touch with John 



Courtney, president, Montreal Micro 68 
Computer Club, Case Postale al Succur Sale, 
Montreal CANADA H4Y 1A2. 

Denver Amateur Computer Society — 
INTERRUPT 

There are newsletters and there are news- 
letters, but DACS' fine publication, 
INTERRUPT, ranks with the superb handful 
that begin to invade the area of the print 
media set aside for magazines. There are 
plenty of interesting and competent features 
on micros. 

Dealing with DACS is a good way to learn 
more about computers; they'll even help you 
get a club started in your area, which is 
probably the best way to share and spread 
knowledge. 

Interested? Get in touch with the Denver 
Amateur Computer Society, POB 6338, 
Denver CO 80206. 

Analytical Engine — Chesapeake 
Microcomputer Club Inc 

Another newsletter that has helped set 
the standard in the micro hobbyist field is 
the Analytical Engine, the publication of the 
Chesapeake Microcomputer Club Inc, 236 St 
David Ct X-4, Cockeysville MD 21030, 
(301) 667-9690. 

Those still looking for a basic Star Trek 
program might want to get hold of 
Volume 1, Number 6. They will also find an 
elementary article on kit building and 
another on assembling a five chip interface 
for those a little further along. The same 
issue contains a "Bibliography of Micro- 
processor Sources," as a handy reference of 
books, software, periodicals and articles. 
They also list similar bibliographies if this 
compendium isn't enough. 

ON LINE - Hardware and Software 
Exchange 

The ON LINE people continue to publish 
a listing of classifieds geared to the computer 
hobbyist: everything a hacker could want 
for sale or swap, you name it. There's also a 
listing of clubs, with meeting schedules. If 
you want to place an ad or if you're just 
looking for a bargain, send a note to ON 
LINE, D H Beetle, publisher, 24695 Santa 
Cruz Hwy, Los Gatos CA 95030. 

Southern New England — Westchester — 
Fairfield 

We often mention NECS, the New 
England Computer Society, in these pages; 
but New England is a fairly large area with 
more than its share of computer buffs, 
especially in its southern parts. If you're a 



142 






SHORT COURSE 

MICROCOMPUTERS: 

PRINCIPLES AND APPLICATIONS 

EL PASO —JUAREZ 

THE UNIVERSITY OF TEXAS 
at EL PASO 

MAY 23 - 27, 1977 

Four day course plus Monday 
evening introductory sessions. Course 
stresses both hardware and software 
considerations of the design and 
application of microprocessors to real 
world problems. The course begins at 
an introductory level and includes 
programming considerations, I/O 
programming and design, memory 
module architecture, system 
evaluation, cost analysis, anda general 
discussion of applications. The lecture 
topics will be illustrated using 
laboratory workshops. 

TUITION 

$375 

WHICH INCLUDES: 

NOTES, CLASS MATERIALS, 

AND 

TUESDAY EVENING FIESTA 

For additional information 

call or write 

Dr. Glenn A. Gibson 

Electrical Engineering Department 

The University of Texas at El Paso 

El Paso, Texas 79968 

(915) - 747-5472 



the microcomputer 



o 



an introduction to 
reality 

now in Canada 



lmsai 
processor 
cromemco 



tell 



and more 



The Computer Place 
186 Queen St. W 
Toronto M5V 1Z1 
416-598-0262 



Focus Scientific 
160 Elgin St. 
Ottawa K2P 2C4 
613-236-7767 



OFF LEASE EQUIPMENT 

Teletype ASR 33 

$809 each 

F.O.B. Your local A J service center. 




Modems and Couplers 
also available. 

ANDERSON 

JACOB5DN 

521 Charcot Ave, San Jose 
California 95131 
(408) 263-8520 



RF MODULATOR KIT 




KIT INCLUDES: 

Modulator (Ch3 t Ch4) Battery Clip 

60 Db Switch On/ Off Switch 

8Ft. RF Cable Instructions 
4 Ft. Video Cable 



• Limited Supply * 
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( Calif. Residents add 6Vt% Tax) 



.tv enrerorszs 

PO DO* ilOII . lunn/KQI* . COIIf or nlo WO88 



South Florida 

Across from the University of Miami 

University Shopping Center 
1238A South Dixie Highway 
Coral Gables, FL 33146 
(305) 661-6042 




Sunny Computer Stores, Inc. 

South Florida's First Computer Store 

We Carry: 

• I MSA I, COMPUCOLOR, VECTOR, 
SOUTHWEST, C.S.C., CROMEMCO 
VECTOR GRAPHIC, SEALS 

• Books, Magazines, Newspapers 
•Sockets, IC's, Printers 

• Digital Cassette Equipment 

• Debugging Equipment 

We offer Classes, Friendly Advice and 
Service 

Hours: Monday - 12 Noon to 9 P.M. 
Tuesday through Saturday — 
10 A.M. to 6 P.M. 



U. S. ROBOTICS 

Makers of fine robots since 1 982, 
announce the next best thing in 1977 

the 

AUTO - ANSWER 
MODEM 

* originate/answer switch means your micro can 

answer calls from other computers or 

terminals. 

Build your own timesharing service. 

(make your hobby pay) 
Start a software exchange. 
Enjoy a new dimension in games: 
man/machine teams in battle! 

* fully assembled and tested. 

* 103 type, runs 0-600 baud. 

* interface with RS232, 20ma and TTL 

* digital modem, crystal controlled. 

* 90-day full warranty. 

* optional S25/yr maintenance contract. 

* 10-day modem-back-money-back guarantee. 

Send $1 05 (shipping, handling and 
Illinois sales tax included) to 

U. S. ROBOTICS, INC. 

Box 5502 
Chicago, IL 60680 
Phone:312-528-9045 



Clubs and Newsletters in- 
formation should be sent 
to BYTE, 70 Main St, 
Peterborough NH 03458, 
attention Peter Travisano. 



Connecticut or Westchester hacker, you 
might want to drop a line to one of these 
addresses: Southern New England Computer 
Society, 257 Willow St, New Haven CT 
06511; Connecticut Microists, 8612 Wendy 
Ln, Westport CT 06800; or Westchester- 
Fairfield Amateur Computer Society, RR 1, 
POB 198, Pound Ridge NY 10576. 

Japan 

Thanks to the Homebrew Computer Club 
in Mountain View CA, we have a rather 
exotic address: that of the Japan Micro- 
computer Club. Those visiting that part of 
the world may want to stop in at the First 
Ohkura Building, 4f 2-1 Nihoubashi, Chuo- 
ku Tokyo JAPAN. 

CACHE Register, Chicago 

The Chicago Area Computer Hobbyists 
Exchange continues to publish CACHE 
Register, a newsletter that seems to lean 
toward abstract information on hardware 
and software; that is, there is very little 
editorializing, just the facts. 

The people at CACHE are always glad to 
lend a hand to the hobbyist who needs 
information of any kind. Write to CACHE, 
POB 36, Vernon Hills IL 60061. , 

Minnesota Computer Society 

We've had some correspondence from a 
new group (new at least to BYTE), the 
Minnesota Computer Society. Those in the 
Twin Cities area who would like to get 
together with other hackers should drop a 
line to MCS, POB 35317, Minneapolis MN 
55435. 

The Association of Time-Sharing Users 

Here's a unique and really useful group 
for those involved in timesharing. AT/SU is 
dedicated to organizing and providing infor- 
mation and a forum for the users and 
industry representatives of remote com- 
puting. They publish a newsletter, Inter- 
active Computing Press Review, a compila- 
tion of pertinent articles from various 
sources; Interactive Computing Directory, a 
two volume directory of remote computing 
users and suppliers updated with each news- 
letter; and Special Reports, a consumer's 
guide to timesharing services. Write the 
Association of Time-Sharing Users Inc, 75 
Manhattan Dr, Boulder CO 80303. 

Philadelphia Area Computer Society 

PACS is publishing a newsletter called 
THE DA TA BUS. Among the features is a 
reprint of Dr Lance Leventhal's fine series of 
tutorial articles on microprocessers, begin- 



ning in November. Bill Goble is writing a 
three piece article entitled "Small Computer 
Bus Structure," which promises to be a 
fairly comprehensive series on bus signals 
and receiving and transmitting the bus. For 
information concerning the Philadelphia 
Area Computer Society and THE DATA 
BUS, get in touch with Bill McGill, Uni- 
versity of Pennsylvania, Moore School Com- 
puting Facility D-2, Philadelphia PA 19174. 

Mobile, Alabama — Anyone Interested in . . . 

. . . SOL-10 Terminal Computers? 
R Downs is and he's looking for other folks 
who are, too. Contact Mr Downs at 205 
Shelton Beach Rd, #53, Saraland AL 36571 . 

New York Amateur Computer Club 

Hackers in and around "Fun City" might 
want to look into the advantages of joining 
the New York Amateur Computer Club in 
care of R Schwartz, 1E 375 Riverside Dr, 
New York NY 10025. 

Ottawa 

The Ottawa Computer Group has grown 
to substantial proportions in a rather short 
time. To get in on their doings, stop in at the 
National Research Council, 100 Sussex Dr, 
Ottawa, on the first Monday of the month 
or write POB 13218, Kanata Ontario, 
CANADA K2K 1X4, (613) 233-9412. 

St Louis Area Computer Club 

The St Louis Area Computer Club met 
recently for the first time, attracting hackers 
from both sides of the Mississippi. Appar- 
ently we have a real mix here of ages, 
vocations and obscure computers. To find 
out more, contact Lou Elkins, POB 1143, St 
Louis MO 631 88, (31 4) 427-61 1 6. 

Panhandle Computer Society 

We've just received word that a new 
computer club has formed, The Panhandle 
Computer Society of Amarillo TX. They 
meet every Friday and boast a membership 
of more than 30. All inquiries should be 
addressed to Tex Everett, 2923 S Spring, 
Amarillo TX 79103, or call (806) 373-8307. 

A Note from Sol Libes re a National 
Personal Computing Society 

I have just finished reading "Some Notes 
on Clubs" in the August 1976 issue, page 4, 
and must take exception to the statements 
you attributed to me. I fear there must have 
been a misunderstanding in our discussions. I 
certainly did not say, in regard to a national 
organization: "Who needs it?", etc. 



144 



I frankly feel there is a need for a 
national organization similar to ARRL. 
There are many reasons for it. Primary 
among them is the need to develop stan- 
dards, both for hardware and software. We 
are currently faced with the problems of 
many manufacturers going their own way in 
equipment and program design and hence a 
great deal of noncompatibility. This causes 
unnecessary expenses for the amateur user. 
For example; we currently have more than a 
dozen different cassette 10 systems which 
are not compatible. This greatly inhibits the 
exchange of software in cassette form. 
Adherence to one recording standard would 
eliminate this problem. 

A single club, or regional organization, is 
not in a position to develop standards and 
influence their adoption. This can only be 
done by a national organization. 

Sol Libes, President 
Amateur Computer Group of NJ 

UCT1 

1776 Raritan Rd 

Scotch Plains NJ 07076 

Sorry about the misunderstanding, So/. I 
came away with the impressions printed in 
that issue . . . CH." 



/BABY! I MICROCOMPUTER 

ARE YOU BUYING A SYSTEM? 

BEFORE YOU DO 
SEND FOR OUR LITERATURE. 
COMPARE OUR SPECIFICA- 
TIONS WITH OUR COMPETI- 
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YOU WILL SEE 

THE BABY! I SYSTEM IS NOT A 
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STM SYSTEMS, INC. 

P.O. BOX 248 

MONT VERNON, N.H. 03057 

603-673-2581 




Not just a pretty face: 

Morrow's presents a front panel with brains— $249-95 



Combination front panel and 
CPU board speeds program 
development and debugging 



Replaces and upgrades ALTAIR/ 
IMSAI front panel and CPU 
boards, or forms the nucleus 
of a custom system. 

This isn't a toy... or a con- 
versation piece... but a tool 
for -serious program develop- 
ment, rivalling the sophisti- 
cation of many minicomputer 
systems. Granted no system 
can make bugs go away : but 
this one, finally, makes them 
manageable. 

Two exclusive operating modes 
give you control over real 
time, allowing you to work on 
a program while it's running. 

The "Control Halt" mode ref- 
uses to let the 8080A CPU go 
dormant upon executing a HALT 
instruction; instead, special 
purpose hardware forces a NO 
OP instruction then passes 
control to the front panel 
program, where you can exam- 
ine and alter processor regis- 
ters .. .memory locations ... and 
I/O ports directly from the 
front panel. 







The "Slow Step" mode allows 
you to run through a program 
at a variable rate from 1 to 
65,000 steps per minute. The 
display indicates the program 
counter and a processor regis- 
ter of your choice. 

Unambiguous readouts replace 
blinking LEDs ; a 12 pad key- 
board replaces time-consuming 
toggle switches . And because 
the front panel/CPU is Altair 
buss compatible, you can build 
a custom system around this 
board using Altair compatible 
peripherals. Also compatible 
with any software written for 
an Altair type buss. 



We've made some strong claims 

in this ad and g^ven the 

way some companies advertise, 
you have a right to be skep- 
tical. In order to dispel any 
doubts, we've put together a 
complete documentation packet 
(schematic, layout, software, 
assembly instructions), avail- 
able for $5.00 postpaid. You 
may be surprised to find out 
we've understated our case. 



x 



m 



BOX 6194 
ALBANY,! 

JCA94706I 






BYTE's Bits 



Jim Warren's Official Rumors About the 
West Coast Computer Faire . . . 

In phone conversation January 5 of 
this year, Jim Warren mentioned some of 
the plans for the banquets which will be 
held during the First West Coast 
Computer Faire. On Friday and Satur- 
day night of the event, there will be 
speakers. Each night's offering will 
represent one speaker about the future 
world, and one speaker commenting 
about the real world of today. On Friday 
April 15, the real world speaker will be 
John Whitney, the computer animation 
and graphics artist who provided a 
fascinating show at the Personal Com- 
puting 76 show in Atlantic City last fall. 
The future world speaker on Friday 
night will be Frederik Pohl, one of the 
better known contemporary science 
fiction writers. On Saturday April 16, 
the real world speaker is Dr Henry 
Tropp, who will speak about his recently 
completed research project on the 
history of computing, commissioned by 
the Smithsonian Institution. The future 
world speaker for Saturday's banquet 
had notbeen finalized asofthe time this 
note was written." 



Want a Used Computer? 

Believe it or not, there exists the 
friendly local used computer broker — 
and there are enough of these fellows 
around apparently (13 in 13 different 
cities) to warrant a somewhat classy 
service organization run by Arthur F 
Phinney and called the Computer Mul- 
tiple Listing Service, located at 3212 
Chichester Ln, Fairfax VA 22030. This 
organization puts out a 16 page pam- 
phlet which describes some of the 
mechanics of computer brokerage and 
the ways in which computer purchases 
can be arranged. We wouldn't expect 
much traffic in $2000 personal systems 
here, but if you want to look into a 
bargain price for a model X big com- 
puter this might be the place to start." 



Notes on "What Is It?" 

In December 1976 BYTE we ran a 
little query on page 96 concerning a 
cross section of an unidentified product. 
The answer appeared in the January 
197 7 issue of BYTE on page 104. The 
question elicited several responses, but 
only one correct response. Floyd Lar- 
gent, of the Abex Corporation, En- 
gineered Products Division, Mill St, 
Athens OH 45701 writes: "The product 
in your "What Is It" photograph is a 
porous plastic used to hold ink for 
computer printout devices." 

But some of the wrong answers were 
just as interesting as the picture itself. 



Attention Manufacturers 

Personal computing equipment man- 
ufacturers and suppliers are invited to 
participate in the 1977 National Com- 
puter Conference personal computing 
exposition to be held in Dallas TX, June 
13-16. The NCC, sponsored by the 
American Federation of Information 
Processing Societies Inc (AFIPS) and 
four of its member societies, will be the 
year's largest gathering of data proc- 
essing users and computer professionals. 

Full information on the Personal 
Computing Exposition, including 
brochure, floor plan, and application 
forms, is available from the AFIPS 
Exhibit Sales Office, 210 Summit Av, 
Montvale NJ 07645, (201) 391-9810. 

The 77 NCC, recognizing the size and 
importance of the personal computing 
market, will feature a commerical exhibi- 
tion by equipment manufacturers and 
suppliers of personal computing prod- 
ucts and services. The Personal Com- 
puting Exposition will be in the North 
Hall of the Dallas Convention Center 
one level below the main NCC exhibit 
hall. Reservations for linear booths 
(minimum size 10 feet by 10 feet 
at a cost ot $600) are currently being 
accepted. As a special service to partici- 
pating exhibitors, packaged booth dis- 
plays are being made available as part of 
the overall cost. 

In addition to the Personal Com- 
puting Exposition, the NCC will also 
feature a Personal Computing Fair where 
individuals and groups will display non- 
commercial systems and equipment. Per- 
sonal computing will also be covered in a 
variety of NCC events including a two 
day program of sessions, and a computer 
club congress." 



Two people identified the item as a 
scanning electron microscope picture of 
a printed circuit board. One person 
identified it as an electron microscope 
picture of "the actual atomic lattice of a 
conducting material, copper wire or 
something ..." (Only problem: Resolu- 
tion for typical electron energies is just 
not that good.) One person opined that 
it was "an experimental optical read 
only memory consisting of micro- 
encapsulated spheres of a black fluid 
sandwiched between two transparent 
planes. A relatively high power beam of 
light is used to write bits by exploding a 
sphere containing the fluid, while a low 
power beam reads the blots created as 
bits." Another identified it as a cross 
section of a bubble memory. The most 
common answer, which actually is not 
far from the mark, was that the picture 
was a cross section of the commonly 
used conductive foam in which inte- 
grated circuits come packaged. In ap- 
pearance, it is probable that a closeup 
photo of such foam might indeed look 
very similar to the photomicrograph of 
the inking matrix. 

We extended Floyd's BYTE sub- 
scription by one year as an informal 
prize on this informal contest." 



Programmers Invited to 
Participate in 1977 National 
Computer Conference 
Programming Contest 

This announcement arrived two days 
after the February BYTE was on the 
press, but if you hurry, you'll be able to 
meet the March I deadline ... by writ- 
ing your own "official entry form" as 
well as the contest entry. 

Programmers who attend the 1977 
National Computer Conference, June 
13-16, in Dallas TX will have an oppor- 
tunity to participate in the 1977 NCC 
National Programming Contest. All con- 
testants will be competing for prizes, 
trophies, and plaques, as well as the 
chance to gain the title of "1977 
National Champion Programmer." 

According to Dr Portia Isaacson of 
the University of Texas at Dallas, 1977 
NCC chairperson, "The 77 NCC special 
activities committee has organized this 
'first' National Programming Contest in 
an effort to involve computer profes- 
sionals more directly in conference acti- 
vities. Approximately 240 applicants will 
be selected to participate in a test of 
logic and programming skills." 

Directing plans for the contest is Dr 
C E Rodriguez of East Texas State 
University. Dr Rodriguez reports that 
there will be no requirement for a 
particular programming language. En- 
trants selected will receive a list of 
specific languages, terminals, and time- 
sharing services to be used in the contest. 
Contestants will be selected based on the 
quality of their solutions to a sample 
problem which will be made available on 
request. 

Deadline lor all entries is a postmark 
no later than March 1 1977. Official 
entry forms and sample problems may 
be obtained by writing Dr C E Rod- 
riguez, Computer Science Dept, East 
Texas State University, Commerce TX 
75428.- 



A New Virginia Polytechnic Institute 
Seminar Program 

David G Larsen forwards these two 
notices of a new series of microprocessor 
related seminars to be held at VPI in 
June of this year: 

Microcomputer Interfacing Work- 
shop, June 9, 10, 11, 1977. 
A three day workshop based on the 
popular microprocessor. Over 20 
operating 8080 computers are avail- 
able for participant use. 
Digital Electronics for Automation 
Workshop, June 7, 8, 1977. 
A two day workshop based on the 
small scale and medium scale TTL 
integrated circuits. Many hours of 
laboratory time with individual 
breadboarding stations will be pro- 
vided along with indepth lectures. 

For more information on these work- 
shops contact Dr Norris Bell, VPI and 
SU Continuing Education Center, 
Blacksburg VA 24061, (703) 951-6328." 



146 



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185 


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only $49.95 



Build Your Own MONITOR 

Now in Stock -NEW 
M3000 - 100 12-inch display module $229.00 

M2000- 155 9-inchdisplay module $208.00 

*Add $10.00 Shipping 



MOTOROLA Exorciser. MEK6800DI 
and MEK6800D2 Compatible Modules 

9601 16 Slot mother board- Inc. Conn. $175.00 

9602 16 Slot card cage 19" rack mount S 72.00 
9610 Utility Prototyping Board S 36.00 
9615 4K Eprom Module (1702A) $350.00 
9620 Parallel I/O Module $375.00 
9626 8K Static Ram Module $350.00 
9650 8 Channel Duplex Ansyn I/O $390.00 

All assembled and tested. Not Kits 



r MlSCELLANY 




BUZZER S.95 




KEYBOARD **Jj*»* Ok - 

TOUCHTONE \*^.X'V „> 
KEYBOARD N§**j£fcJi 

FOR TELEPHONE \*HJ^--- — 
Uwwlth MK5065N inngiand torn 
(l.nlnr H3 579H.-c<yitsl 
Crymi n«H*bfi lor S4.95 

Only $9.95 



MM5311 
MM5313 
MM5314 
MM5316 
MM5375 



NOW l 

A 19 key Number K.yboinl compitiblt 
1 oui 63 K»y KiybMrd £*me 
mlicnini ar.il (jgnovi Ktyl (of tn 9 
110,300. FDX'HDX. minui Auto LF 

1.95 FIRST TIME OFFERED 



r»~nl 19 kl 



j. 03 Kl 



▼ variable resistors 



25 60 
55100 
105 500 
505up 



[ CORCOM EMI FILTER 

»CORCOM2B4 2A O.ily S4.95 

115'730V50 400MI Tell 2I00WOC 



ROTARY SWITCH 







CaUFornIa IncIustrIaI 

Post Office Box 3097 B • Torrance, California 90503 




SFE FRY^ U N IVAC 



The famous Sperry Univac 1710 Hollerith keyboard assembly 
is now available from California Industrial for only $24.88 
The ideal computer input device for accountants and 
mathematicians. The numeric keys are placed on the lower 
three rows to resemble a ten key adding machine. This 
format allows one handed numeric data entry. 
Original cost was $385. Used but guaranteed in excellent 
condition. Complete with documentation. 




'■^;"^i, ; '. Mi 'tfr* 



Wire Wrap Project Board 

The ideal prototype board for those one of 
a kind projects. Each board accommodates 
300 integrated circuits. 



100 PIN 

IMSAI/ALTAIR 
Edge Connector 



Altair, Imsai compatible gold plated, dual 50 
(.125 centers) three tier wire wrap edge 
connector. 3 for $13.50 




1750, 



63 key 
KEYBOARD 



Uncoded computer keyboard. Contains: 63 
reliable gold plated SPST switches. ASCII 
Kit: components and printed circuit board. 
$35.00 additional. 



POWER SUPPLIES 



. ySTICK S S 



So 




This joystick feature four 100K potentio- 
meters, that vary resistance proportional to 
the angle of the stick. Perfect for television 
games, quad stereo and radio controlled 
aircraft. 




5 volt 2.2 Amp regulated power supply. Also 
delivers 12 volts at A Amps unregulated. 
Perfect for TTL applications. 



Power Transformer 



$ 4.3S 



Input 117ac. Output-21v 5A center 
tapped. Suitable lor 12v. 5A. or 5v. 
10A power supply. Four other wind- 
ings at lower currents. 




CALCULATOR 
KEYBOARD 




198 



Ideal for keyless entry systems, burg- 
lar alarms. Touch Tone or hexa- 
decimal computer input code. 



As Low As 



7400 


^ 


7476 


39 


7401 


10 


7479 


3 99 


7402 


ID 


7480 


79 


7403 


1Q 


7482 


99 


7403 


19 


7483 


99 


7404 


14 


7485 


99 


7405 


14 


7486 


.49 


7406 


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7488 


3.40 


7407 


?5 


7489 


2.79 


7408 


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7490 


49 


7409 


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7491 


99 


7410 


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7492 


49 


7411 


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.49 


7412 


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79 


7413 


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79 


7414 


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79 


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399 


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49 


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1.79 


7425 


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1.99 


7426 




74120 


1.79 


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44 


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59 


7433 


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74126 


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.49 


7438 


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99 


7439 


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89 


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99 


7441 


f-4 


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99 


7442 


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199 


7445 


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1.19 


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74151 


99 


7447 


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74153 


89 


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4H 


74154 


99 


7450 


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74155 


.99 


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1.29 


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74157 


99 


7454 


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2 99 


7460 


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74160 


1.19 


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74161 


99 


7472 


^ 


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149 


7473 


39 


74163 


99 


7474 


SK) 






7475 


49 







74164 
74165 
74166 
74167 
74170 
74173 
74174 
74175 
74176 
74177 
74180 
74181 
74282 
74184 
74185 
74186 
74190 
74191 
74192 
74193 
74194 
74195 
74196 
74197 
74198 
74199 
74273 
74290 
74366 
74390 



4002 
4006 

4007 
4008 
4009 
4010 
4011 
4012 
4013 
4014 
4015 
4016 
4017 
4018 
4019 
.4020 
4021 
4022 
4023 
4024 
4025 
4027 
4028 
4029 
4030 
4032 
4033 
4035 
4040 
4041 
4042 
4043 
4044 
4046 
4047 



$3.98 Digital Clock 




Manufactured for the Panasonic 
clock radio. The clock mechanism 
trips a microswitch upon reaching 
your preset wake-up time. 




3^N » 

RIBBON WIRE 





3O0H 


.79 


340T-24 


179 


301H 


39 


350N 


99 


301CN 


39 


351CN 


65 


302H 


129 


370H 


1 29 


304H 


129 


370N 


1 29 


305H 


99 


373N 


3 19 


307H 


49 


377N 




307CN 


39 


380N 


1.39 


308H 


99 


381N 




308CN 


99 


382N 


179 


309H 


109 


NE555V 


49 


309K 


99 


NE556 


1.29 


310H 


1 19 


NE565H 


; ■■ .: 


310CN 


1 19 


NE565N 


1 79 


311H 


99 


NE566N 


1 25 


311N 


99 


703CN 


45 


312H 


199 


709H 


33 


318H 


179 


709N 


39 


318CN 


149 


710N 


79 


319CN 


129 


711H 


; 


320K-5 


139 


711N 


a 


320K-12 


139 


723H 


.55 


320K-15 


139 


723N 


55 


320T-5 


175 


725H 


349 


320T-8 


175 


733H 


'..49 


320T12 


175 


733N 


99 


320T-18 


175 


739N 


1.19 


3201-24 


1.75 


741N 


.09 


324N 


179 


747N 


■5 


339N 


169 


748H 


39 


340K-5 


195 


748N 


.39 


340K-8 


195 


1414N 


1 75 


340K-12 


195 


1458 


.69 


340K-15 


195 


1496N 


95 


340K-18 


195 


2111N 


195 


340K-24 


195 


2901N 


295 


340T-5 


1.79 


3065N 


.69 


340T-12 


1.79 


3900N 


.49 


340T-15 


1.79 


3909N 


1 19 



"We want to give ihem away — but our accoun- 
tants won't let us. So instead we are selling them 
at cost And therefore must limit the purchase ot 
the SN7400 and the LM741 to 50 per customer. 



ID 

DISC 

capacitorsI 



Your Choice .1 or .01 




*.98« 

3000 Mfd. 
50v. 

ELECTROLYTIC 
CAPACITOR 



LINE CORD 

Nine foot grounded 



DIODES 

$.98 

25. . .1N4148 
20. . .1N4002 
(1 amp 100v) 
15. . .1N4005 
(1 amp 600v) 



Photoconductor 
Cells 

3for*98 

lOohm to IOO K 



Wire Wrap 




2 for 

1 .98 

Two gold plated, three tier 
wire wrap DIP sockets. 
Your choice 14 orlSnin 



i * 

|^5L 5-WAY 

\§gf BINDING 
?3F POSTS 



Calculator Pad 



10 for 

*.98 

TRANSISTORS 

2N3904 NPN 
2N3906 PNP 




MONSANTO 

Common Cathode 

.4" GREEN $1.25 



cfs 

TRIMMER POTENTIOMETERS 



IOKohms 

5for*.98 



$J 



$ .98 

fast charge 




1.5T0 3VDC v?^K?^ ") 

MICRO 
BUZZER 



50FT.for*.98 

30 awg. 

KYNAR 

wire* 

OK HOBBY WRAP-30 
wire wrap&strip tool 



$5.50 




30. 

TEFL 
WIP 

90, 



Your WW FT. 

Choice TEFLON 

198 wmE 



PFT. 

HOOK-UP 

WIRE 




J SOLDERLESS 

TERMINALS 

16-14 or 22-18 



SPOT 

MINIATURE* 
TOGGLE SWITCH 



Sfor MrfO 

SWITCHES &+\ 




SPST 
MICROSWITCHES 



'.98. 



"f^ 



DPDT 

ROCKER SWITCH 



All merchandise told by California Industrial It premium gn 

Orders are snipped the same day received. 
PLEASE INCLUDE $1.00 SHIPPING ON ORDERS UNDER $10.00 
California residents add 6% sales tax • Money back guarantee. 




COMPUTER 

WAREHOUSE 

STORE 



DEPT. B, 58A COMMONWEALTH AVE. 
BOSTON, MA 02215 617/261-2701 



COMPONENTS FOR 

SYSTEMS 



EATURES OF THE MONTH 

GREEN PHOSPHOR 
VIDEO MONITOR 





SYKES COMPUCORDER 

$950 + $35 SHIPPING 

GREAT CASSETTE RECORDER 

OFFERS 3-6M BIT STORAGE 

TRANSFER RATE OF 500 CH/SEC 

AT 1000 BPI. READ WRITE SPEED 5 IPS RECORDING 

BIT SERIAL. BIPHASE ENCODED WITH VARIABLE 

BLOCK LENGTHS UNDER PROGRAM CONTROL 

TECHTRAN 4100 $595 

TAPE CASSETTE DRIVE + $35 SHIPPING U.S. 
VERSATILITY PLUS IS YOURS WITH THIS ORIGINAL 
COST $3200 DRIVE. JUST PLUG IT IN RS232. CAN 
RUN DIRECTLY FROM TERMINAL INDEPENDENT OF CPU. 
FULL EDIT CAPABILITY, ALL FUNCTIONS UNDER SOFT- 
WARE CONTROL. LIMITED QUANTITY AVAILABLE 

TALLY T132 

7 x 8 DOT MATRIX IMPACT 

PRINTER HAS A SINGLE 

LINE DYNAMIC MEMORY AND 

A UNIVERSAL INTERFACE TO 

ACCEPT PARALLEL DATA, FORMS 

TO U-7/8 IN. SIDE, SIMPLE PRINTING MECHANISM 

USES 132 SOLENOID HAMMERS AND TWO STEPPER MOTORS 

FOR 100 LPM, 132 COLUMNS, 6*4 CHARACTERS 

$950 + SHIPPING 150 lb. 



$150 




TOP QUALITY CRTS FROM A MAJOR VENDOR ... 
NOT JUST A REWORKED TV SET. STANDARD 1V 
P TO P COMPOSITE VIDEO INPUT, 10 MHz BAND 25 SHIPPING 
WIDTH, RASTER SCAN 12 x 12 x 13 IN., WITH POWER SUPPLY 
VIDEO AMPLIFIER, DRIVING CIRCUITRY, VENTILATION MUFFIN 
FANS, 7 x 9 IN. HORIZONTAL VIEWING AREA UP TO 2k LINES 
x 80 CHAR., ANTIGLARE h IN. ETCHED GRADIENT DENSITY FACE 
PLATE, P39 GREEN PHOSPHOR FOR BETTER VIEWING EASE, ON/OFF 
BRIGHTNESS CONTROLS, 115VAC, 60 W. (SPOT SIZE .015 IN. 
NOMINAL) ... TRULY A COMMERCIAL UNIT BUILT TO WORK IN 
A DEMANDING ENVIRONMENT. WE'VE RUN THREE OF THESE OFF 
OUR SwTPC TERMINAL KIT AT ONCE FOR DEMONSTRATIONS. 
• ••••••• 

ALLanASR33isand MORE! 

WE'VE SOLD OUT 3 TIMES ON THIS HEAVY-DUTY 
^TELETYPEWRITER. THIS SHIPMENT IN GREAT 
CONDITION OFFERS RS232 INTERFACE, QUIET 
OPERATION, 10 CPS BUILT-IN PAPER TAPE 
PRINTER/PUNCH, ELECTRIC TYPEWRITER KEY- 
BOARD WITH ADDITIONAL 10 KEY NUMERIC PAD, 
YOUR CHOICE OF FRICTION OR SPROCKET F^ED, 
LIGHTED PLATEN AREA FOR EASY READING , 
STANDARD PAPER AND TAPE, SUPPORTED BY 
OLIVETTI, IMPACT PRINTER GOES UP TO 6 
bCOPIES, VERTICAL SPACING ADJUSTABLE. 




$950 



1 



-DAY SHIPMENT 
KITS, MPUs, CPUs 



( FROM OUR 
STOCK ) 



LSI ADM 3 KIT $875 

UPPER/LOWER CASE OPTION 100 
10 KEY NUMERIC PAD 150 

IMSAI..8080A KIT 5 SLOT.. $599 
8080A KIT 22 SLOT. . 651 
4K MEMORY KIT 139 

VIKING 100 PIN CONNECTOR. . 
HEAVY DUTY $ 5 

SERIAL I/O KIT 125 

PROM ^-512 KIT 165 

UCRI-1 KIT 59 

CABLE A KIT 18 

SWTPC. .6800 KIT.. • $399 

MPA 1^5 MPB UO 

MPC ^0 MPD 35 

MPE 15 MPF 30 

MPM 80 MPMx... k$ 

MPP 35 MPL 35 

MPS 35 MPAb. 1^.50 

MPMb.. 1*4.50 MP8b. .. 30 
MPCb.MPSb.MPLb ea. 9. 50 
CONN. SETS MPU/MEM 2.50 
CONN. SETS INTERFC 2 

AKBA 5 GT61-. . 99 

AC30 AUDIO INTRFC 79.50 

PP^O PRINTER 250 

CT 102^ TERM. KIT.. 275 

CTI 175 KBD ^9-95 

CTP... 15-50 CTS.. 39-95 

CTCA 15-50 

ALL SWTPC UNITS ARE KITS 



KIM 1 . .6502 $2451 

KIM 2. .^K 179 I 

KIM 3..8K 289J 

MANUALS PACKAGE 1 5 1 

ICOM FLOPPIES J 

FF36-1 $1195' 

FF36-2 1895' 

360-58 3O0J 

S171 H 250l 

TARBELL AUDIO 

CASSETTE KIT $ 1 20 f 



INTERSIL INTERCEPT JR $281 j 

12K RAM Ii<5| - 

ROM/PROM BOARD 7^.65| 

YOU ADO MEM CHIPS ■ 

SERIAL 1/0 81 .50 j 



+ SHIPPING 165 

DATAPOINT 3300-200 

THERMAL PRINTER 

SURPRISING LITTLE THERMAL PRINTER USES WELL^ 

RESPECTED AND FIELD PROVEN NCR EMT-1-AE 

PARALLEL PRINTER WITH ADDITIONAL CIRCUIT 

BOARDS TO PROVIDE SERIAL RS232 INTERFACE, 

PRINTS UP TO 30 CPS. 110 VAC PS. USES WIDELY 

AVAILABLE NCR PAPER, 96 CHAR. ASCII, 80 COL., 

CRT COMPATIBLE 5 x 7 DOT MATRIX, SOLID STATE sHIPPlWu S 

WITH LESS THAN 25 MOVING PARTS. 

DATAPOINT CASSETTE 

3300-300 $195* $25shipping u.s. 

SMALL STYLIZED CASSETTE RECORDER SERVES 

AS ADJUNCT BETWEEN CRT TERMINAL AND CPU. ON LINE STORAGE 
OFF LINE MESSAGE PREPARATION, ^50,000 CHAR. PER CASSETTE 
NO POWER SUPPLY, I/O UP TO 2*»00 BPS. 



AUDIO VISUAL BOARD 



125 



NATIONAL SEMICONDUCTOR | 

SC/MP KIT $ 99| 

KEYBOARD KIT 95J 

SMOKE 16 K MEMORY $59s' 

shi pping on ki ts | 

under $100 $5 

over S100. ... $10 1 

WRITE FOR OUR COMPLETE I 

CATALOG j 

covering kl* ts , used equipment 1- 

and our wide range of ■ 

avai lable books 



KLEINSCHMIDT 311 $250 7 SHIPplNG 

THIS 30 CHAR/SEC DRUM PRINTER SITS IN A SOUND-PROOF 
ENCLOSURE, Gk CHAR., PARALLEL INPUT, 80 CHAR/LINE, 
ORIGINAL PRICE $2100 WITH ENCLOSURE 

"15iGFTwJNICS~D507~~ ~~~~~ " 

PAPER TAPE TRANSMITTER -$■ 

BEAUTIFUL 5' "ENCLOSED CABINET 
PROVIDES TREMENDOUS SUPPLY OF GOODIES INCLUDING DIGITRONICS 
2500 PHOTOELECTRIC PAPER TAPE READER, HEAVY DUTY POWER SUPPLY, 
3 MUFFIN FANS, POWER CONTROL PANEL, CIRCUIT BOARDS, RELAYS, 
CABLES. SOME HAVE PAPER TAPE HANDLERS, ALL ON CASTERS 




$95 



+ SHIPPING ^00 lb. 



ITO ORDER:! 
ENCLOSE CHECK FOR FULL 
PRICE PLUS SHIPPING 
CHARGES (IN MASS, ADD 
5% SALES TAX) 
CLEARLY IDENTIFY SHIP- 
PING ADDRESS. 
^DE^^^JTEM^B^MOD^L 

™day™hTpmen"T , it BANK 

CHECK OR MONEY ORDER 




DATAPOINT SERVO PRINTER in desk console 

$395 + SHIPPING 285 lb. 
IDEAL UNIT TO BUILD A SYSTEM AROUND. 
BOTH UNI VAC AND SINGER BUILT THESE 
PRINTER MECHANISMS WHICH OPERATE AT 
30 CPS FROM A ROTATING WHEEL. 65 CHAR. 
USES STANDARD PRINTOUT OR TYPEWRITER 
PAPER. PINWHEEL IS INTERCHANGEABLE. 

UNIVAC 0769-06 PRINTER MECHANISM ONLY. ..$295 
INCLUDES MOTOR/PRINT WHEEL + SHIPPING 751 b ■ 



VISIT OUR STORE: 




9 TO 9 WEEKDAYS; 




THE SC/MP at $95.00 

SC/MP, the Microprocessor kit from National 
Semiconductor includes everything you need to 
build a completely functional microprocessor 
system — featuring the National SC/MP micro- 
processor — the low cost microprocessor for 
every application: Text Systems and Instrument 
Control; Machine Tool Control; Small Business 
Machines; Word Processing Systems; Educational 
Systems; Multiprocessor Systems; Proces Con- 
trollers; Terminal Control; Laboratory Instru- 
mentation; Sophisticated Games; Automotive 
Controller and Appliance Controllers. 

The kit, neatly packaged with all the com- 
ponents and literature you need, in a looseleaf 
binder, includes: The SC/MP Microprocessor 
— a single-chip Central Processing Unit in a 40- 
pin, dual in-line package. Features static operations, forty-six instruc- 
tion types; single-byte and double-byte, software controlled interrupt 
structure, built in serial input/output ports; bidirectional 8-bit TR I- 
STATE R bus, parrallel data/port and latched 12-bit TRI-STATE R 
address port. ROM - 512 bytes (8-bits/byte) of pre-programmed Read- 
Only-Memory containing KITBUG — a monitor and debugging program 
to assist in the development of your application programs, KITBUG 
provedes teletypewrite input/output routines and allows examination, 
modification, and controlled execution of your programs. RAM-256 
bytes of static read/write memory for storage of your application 
programs. Transfers of data to and from RAM are controlled by SC/MP 
and KITBUG. Teletypewriter Interfact including buffer and drive 
capability for a 20 MA current loop interface. Voltage Regulator. 
Data Buffer— providing interface between memory and bidirectional 
data lines. All the literature you need, including schematics and pro- 
gramming manuals. Timing Crystal— providing 1.000 MH? timing 
signal. Plus all the passive components and circuit board with 72 pin 
edge connector required to build and interconnect your microprocessor 
system with external hardware. 



SC/MP 
KEYBOARD 




ASC II KEYBOARD 




1 



(Reg $58 85) $53.00 



This 63 key ASC II Encoded Keyboard kit was designed and manufactured 
by Electronics Warehouse Inc. Features: single 5 volt D.C. supply, utilizing 
only TTL logic elements (no MOS devices to blow), TTL drive capability(each 
of the eight bits of ASC II output will drive the equivalent of ten standard TTL 
inputs without external buffer drivers), de-bouncing, upper and lower case 
fully ASC II, 8 bit parallel output. In addition to the alpha-numeric and symbol 
keys available on a regular keyboard, the following keys are utilized: escape, 
back-space, tab, line-feed, delete, control, shift-lock, shift-{2 keys), here-is, 
control-release. 

Kit includes: 63 key keyboard, P.C. board, all required components and as- 
sembly manual with ASC II code list. 
Optional: 1. Parity bit- add $1.00 Aluminum enclosure $39.- 

2. Serial output - add $2.00 
Note: If you already havethisteletypekeyboardyoucanhavethekitwithout 
it for $36.00 (reg. $39.85). Dealer inquires invited. 



This is a g reat kit for engineers and com- 
panies who don't have access to a Teletype. 
Itisalow-costteaching, learning, and 
developing tool for hobbyists, professors, 
students, and electronics entrepreneurs of 
all levels. 



National'snew Keyboard Kit now gives 
SC/MP Kit users a low-cost input/output 
capability. This new kit replaces the Tele- 
type* normally required by the SC/MP Kit 
and allows users to evaluate the SC/MP 
CPU and to develop a variety of application 
software. 

The heart of SC/MP Keyboard Kit is a ROM 
firmware package (512 bytes) called 
SCMPKB. TheSCMPKB ROM replaces the 
"Kit Bug" ROM originally supplied with the 
SC/MP Kit and allows the effective use of 
the hexadecimal keyboard, to execute 
programs, to examine or modify the con- 
tents of memory and the SC/MP registers, 
and to monitor program performance. 



There is a hole pattern for additional inte- 
grated circuits on the SC/MP Kit PC card. - 
By following the simple instructions in the 
SC/MP Keyboard Kit users manual, one 
can add buffers, decoders, drivers, multi- 
plexers, etc. Simply replace the Kit Bug 
ROM (supplied in the SC/MP Kit) with the 
new SCMPKB ROM, connect the pre- 
assembled Keyboard cable connector to 
the kit card, and you are ready to go! 

National's Keyboard Kit comes complete 
with manual, all required integrated circuits 
resistors, keyboard display cable con- 
nector assembly, wire wrap connectors, 
precut wires — even a hand-held wire wrap 
tool. 



SWITCHES 

10 Position rotary switch 
by oak manuf. $1.00 per 4 

8 position, 1 off switch in T05 can 
$.69 2 for $1.00 




ROCKER SWITCH 

SPST normally open contact rating 6A 250VAC 
solder $ .50 ea $2.00 per 6 




MINIATURE TOGGLE SWITCH 

SPST P.C. MOUNT $.99 



MINIMUM ORDER $5.00 

Shipping & Handling: 

KEYBOARD or SC/MP - $3.00 + $.50 Insurance 

all others -$1.00 

California residents add 6% sales tax. 

ELECTRONICS WAREHOUSE Inc. 

1603 AVIATION BLVD. 

REDONDO BEACH, CA. 90278 

TEL. (213)376-8005 

WRITE FOR FREE CATALOG 
You are invited to visit our store at the above address 



World's Lowest 
IC Prices 



SPECIAL PRICES 



MEMORIES 
Rams 



2102 
Proms 



1.50* 



82S23/S123 1.95* 



TTL 




7400 


.12* 


7402 


.14 


7403 


.14* 


7404 


.16* 


7407 


.20 


7410 


.12* 


7420 


.12* 


7427 


.25 


7438 


.20* 


7440 


.12* 


7441 


.65* 


7445 


.45 


7447 


.75 


7450 


.14 


7451 


.14* 


7473 


.22 


7474 


.23 



7480 

7493 

7495 

74107 

74109 

74116 

74123 

74141 

74145 

74150 

74151 



.40* 

.50 
.49 
.29 
.30 
1.50 
.45* 
.80* 
.75 
.60* 
.60 



* 

74152 
74155 
74157 
74160 
74161 

74163 
74165 
74173 
74174 
74175 
74177 
74180 
74181 



74192 

74193 

74194 

74198 

9602 

9300 

9312 

SCHOTTKY 

74S01 

74S02 

74S37 

74S38 

74S85 

74S113 

74S139 

74S140 

74S153 

74S172 

74S174 

74S175 

74S181 

74S197 

74S257 



.90 
.60 
.60 
.75 
.75* 

.75* 

.80 
1.25 

.75 

.75* 

.70 

.80 
1.50 



.70* 
.70* 
.85 
1.25 
.50* 
.75 
.70 



.25 

.25 

.40 

.60 
2.00 

.80 
1.50 

.50 
2.50 
4.50 
2.05 
2.05* 
4.50 
2.20 
1.50 



HIGH SPEED 




74H00 


.20 


74H01 


.20 


74H04 


.20 


74H10 


.20 


74H11 


.20 


74H40 


.20 


74H51 


.20 


74H52 


.20 


74H74 


.40 


74H103 


.50 


74H106 


.50 



LOW POWER 

SCHOTTKY 

74LS00 

74LS02 

74LS08 

74LS10 

74LS27 

74LS73 

74LS75 

74LS151 

74LS153 

74LS157 

74LS161 

74LS163 

74LS164 

74LS174 

74LS175 

74LS193 

74LS221 

74LS251 

74LS253 

74LS257 

74LS258 

CMOS 
4001 
4002 
4006 



.29 

.29 

.29 

.29 

.30 

.45 

.65 
1.10 
1.10 
1.10 
1.50* 
1.50 
1.50 
1.10* 
1.50 
1.50 
1.50* 
1.50 
1.50 
1.50 
1.50 

.16* 

.16 

.90 



4007 


.16 


4008 


.70 


4011 


.16* 


4012 


.16* 


4013 


.30* 


4015 


.80 


4016 


.35* 


4019 


.70 


4020 


.90 


4021 


.95 


4023 


.16* 


4024 


.75 


4025 


.20* 


4027 


.40 


4028 


.60 


4030 


.35 


4040 


.95 


4042 


.60 


4043 


.75 


4044 


.70 


4049 


.35* 


4050 


.35* 


4066 


.65 


4068 


.35 


4069 


.16 


4071 


.16 


4073 


.16 


4075 


.16 


4516 


.85 


4528 


.75 


4585 


.85 


LINEARS 




NE536T 


2.75 


NE555V 


.43 


NE556A 


.90 


1456V 


.75 


1458V 


.52 


566V 


1.25 


567V 


1.35 


540L 


2.00 



Order Minimum $10.00. Add $1.00 shipping and handling charge per order. California residents add 6% sales 
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74LS00 


$0 


36 


74LS01 





3b 


74 LS02 





36 


74LS04 





42 


74LS08 





38 


74LS10 





36 


74LS11 





38 


74LS14 


1 


38 


74LS20 





36 


74LS21 





38 


74LS22 





38 


74LS27 





38 


74LS30 





36 


74LS32 





38 


74LS37 





53 


74LS38 





53 


74LS42 


1 


2S 


74LS74 





56 


74LS75 





85 


74LS109 





60 


74LS124 


2 


SO 


74LS125 





75 


74LS126 





75 


74LS132 


1 


50 


74LS138 


1 


38 


74I.S139 


1 


38 


74LS1SS 


1 


38 


74LS157 


1 


25 


74LS160 


1 


85 


74LS161 


1 


85 


74LS162 


1 


85 


74LS163 


1 


85 


74LS168 


1 


87 


74LS169 


1 


87 


74LS174 


1 


38 


74LS175 


1 


35 


74LS221 


1 


38 


74LS240 


1 


88 


74LS257 


1 


25 


74LS258 


1 


38 


74LS273 


2 


25 


74LS283 


1 


20 


74LS367 


1 


00 


74LS368 


1 


00 


74LS377 


1 


88 


74LS378 


1 


38 


81LS95 


I 


13 


81LS96 


1 


13 


81LS97 


1 


13 


81LS98 


1 


.13 



We Now Distribute Knowledge! 

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VOL 3 "8080 Programming for Logic Design" #4001 $7.50 






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25 PIN RS-232 
CONNECTORS: sub- 
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Male plug with 
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part #D825P 

S3. 95 

Female jack, 
part #DB25S 
S3. 95 



309K +5V, 1A.. 

320/12T..-12V, |A. 
3W5K...+5V, IA.. 
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340/8K. 
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+8v, IA. . 
+12V, 1A. 
+15V, IA. 
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Now you have a choice — specify wire 



wrap pins (illustrated) 
tail with .250" row spac- 
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Wire wrap part 8 
S-J00WW. Solder- 
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#S-100ST is ideal for 
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solder 




{ 

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14 pin 10/$1.95 

16 pin 10/$2.15 

18 pin 10/$2.75 

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22 pin 10/$3.50 

24 pin 10/$3.60 

36 pin 10/$5.50 

40 pin 10/$6.15 



3 level, gold plated 

14 pin ..10/$3.70 

16 pin 10/$3.85 

18 pin l/$0.75 

22 pin 1/S1.50 

24 pin 1/51.00 

28 pin 1/51.25 



40 pin 1/$1.75 



J 



CRYSTALS 

WE OFFER TWO DIFFERENT TYPES OF CRYSTALS — 
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18.6*1, 19.200, 20.480 : 30.720, 31.500, 32.768, 
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and 2*0.00. 

SENTRY XTALS: Series mode, fundamental, wire leads. 
Choose from U, 5, 8, 9, 10, 12, 15, 18, and 20 MHz. 
(Note: 18 MHz = 8080 clock, k MHz = PACE clock freq.) 



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BILL GODBOUT ELECTRONICS 
BOX 2355, OAKLAND AIRPORT, CA 94614 



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add 5% hand 1 ing/shping . 
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^p 7400NTTL^p^ 

SN7400N .16 SN7459A .25 



SN7400N 
SN7401N 
SN7402N 
SN7403N 
SN7404N 
SN7405N 
SN7406N 
SN7407N 
SN7408N 
SN7409N 
SN7410N 
SN7411N 
SN7412N 
SN7413N 
SN7414N 
SN7416N 
SN7417N 
SN7420N 
SN7421N 
SN7422N 
SN7423N 
SN7425N 
SN7426N 
SN7427N 
SN7429N 
SN7430N 
SN7432N 
SN7437N 
SN743BN 
SN7439N 
SN7440N 
SN7441N 
SN7442N 
SN7443N 
SN7444N 
SN7445N 
SN7446N 
SN7447N 
SN7448N 
SN7450N 
SN7451N 
SN7453N 
SN7454N 



SN7459A 

.16 SN7460N .22 SN74154N 

.21 SN7470N .45 SN74155N 

.16 SN7472N .39 SN74156N 

.18 SN7473N .37 SN74157N 

.24 SN7474N .32 SN74160N 

.20 SN7475N .50 SN74161N 

.29 SN7476N .32 SN74163N 

.25 SN7479N 5.00 SN74164N 

.25 SN7480N .50 SN74165N 

.18 SN7482N .98 SN74166N 

.30 SN7483N .70 SN74167N 

33 SN7485N .89 SN74170N 

45 SN7486N .39 SN74172N 

70 SN7488N 3.50 SN74173N 

35 SN7489N 2.49 SN74174N 

.35 SN7490N .45 SN74175N 

.21 SN7491N .75 SN74176N 

.33 SN7492N .49 SN74177N 

.49 SN7493N .49 SN74180N 

.37 SN7494N .79 SN74181N 

29 SN7495N .79 SN74182N 

29 SN7496N .89 SN74184N 

37 SN7497N 4.00 SN74185N 

.42 SN7410ON 1.00 SN74186N 

.26 SN74107N .39 SN74187N 

.31 SN74121N' .39 SN74188N 

.27 SN74122N .39 SN74190N 

.27 SN74123N 50 SN74191N 

.25 SN74125N .60 SN74192N 

.15 SN74126N .60 SN74193N 

.89 SN74132N 1.09 SN74194N 

.59 SN74136N .95 SN74195N 

75 SN74141N 1.15 SN74196N 

.75 SN74142N 4 00 SN74197N 

75 SN74143N 4.50 SN74198N 

81 SN74144N 4.50 SN74199N 

.69 SN74145N 1.15 SN74200N 

.79 SN74147N 2.35 SN74279N 

.26 SN74148N 2.00 SN74251N 

27 SN74150N 1.00 SN74284N 

.27 SN74151N .79 SN74285N 

.20 SN741S3N .89 SN74367N 
MANY OTHERS AVAILABLE ON REQUEST 

20% Discount for 100 Combined 7400's 



2.20 
15.00 
6.00 
3 95 



CD4000 
CD4001 
CO4002 
CD4006 
CD4007 
CD4009 
CO4010 
CD4011 
CO4012 
CO4013 
CO4016 
CD4017 
CD4019 
CD4020 
CD4022 
CD4023 
CD4024 
CO4025 
CD4027 
CO4028 
CD4029 
CD4030 



25 



CMOS 



CD4035 
C04040 
CDJ042 
CD4Q44 
CD4046 
CDJ047 
CD4049 
CD4050 
CD4051 
CD4053 
CD406O 
CD4066 
CD4069 
CD4071 
CDJ081 
CD45I1 
CD4518 
CD4566 
74 COO M 
74C02N 



2.50 
2 50 
3.00 



74C04M 

74C10N 

74C20N 

74C30N 

74C42N 

74C73N 

74C74 

74C90N 

74C95N 

74C107N 

74C151 

74C154 

74C157 

74C160 

74C161 

74C163 

74C164 

74C173 

74C193 

74C195 

MC1044 

MC14016 



2 15 
3.25 

3 25 
300 
3 25 



LW300H 80 

LM301H .35 

LM301CN .35 

LM302H .75 

LM304H 100 

LM305H .95 

LM307CN 35 

LM308H 100 

LM308CN 1.00 

LM309H 1-10 

LM309K .99 

LM310CN 1.15 

LM311H .90 

LM311N .90 

LM31BCN 1-50 

LM319N 1 30 

LM320K-5 1.35 

LM320K-5.2 1.35 

LM320K-12 1.35 

LM320K-15 1.35 

UUI320T-5 175 

LM320T-5.2 1.75 

LM320T-8 1.75 

LM320M2 1.75 

LM320T-15 1.75 

LM320T-18 1.75 

LM320T-24 5.75 

LM323K-5 9.95 

LM324N 1.80 

LM339N 170 

LM340K-5 1.95 

LM340K-6 1.95 

LM340K-8 1.95 

LM340K-12 1.95 

LM340K-15 1.95 

LM340K-18 1.95 

LM340K-24 1.95 

LM340T-5 1.75 

LM340T-6 1.75 

LM340T-8 1.75 

LM340T-12 1.75 

LM340T-15 1.75 

LM340T-18 1.75 

LM340T-24 1.75 

LM350N 1.00 

LM351CN .65 



LINEAR 



LM370N 

LM373N 

I.M377N 

iM3B0N 

LM360CN 

LM381N 

LM382N 

NE501K 

NE510A 

NE531H 

NE536T 

NE540L 

NE5S0N 

NE555V 

NE560B 

NE5616 

NE5628 

NE565H 

NE565N 

NE566CN 

NE567H 

NE567V 

LM703CN 

LM709H 

LM709N 

LM710N 

LM711N 

LM723H 

LM723H 

LM733N 

IM739N 

LM741CH 

LM741CN 

LM74M4M 

LM747H 

LM747N 

LM74BH 

LM748N 

LM1303N 

LM1304N 

LM1305N 

LM1307N 



LM1310N 2.9! 

LM1351N 1-6! 

LM1414N 1.7! 

LM1458C .6 

LM1496N 9 

LM1556V 18: 

LM2111N 1.9: 

LM2901N 2.9 

LM3065N 6 

LM3900N 5 

LM3905N 6 

LM3909 1.2 

LMS556N 1.8 

MC5558V 10 

LM7525N .9 

LM7535N 1.2 

B03BB 4.9 

LM75450 .4 

75451CN .3 

75452CN .3 

75453CN .3 

75454CN .3 

75491CN .7 

75492CN .8 

75494CN .8 

RCA LINEAR 

CA3013 2.1 

CA3032 2.5 

CA3035 2.4 

CA3039 1.3 

CA3046 1.3 

CA3059 3.2 

CA3060 3.2 

CA3O80 .8 

CA3081 2.0 

CA3082 2.0 

CA3083 1.6 
CA3086 
CA30B9 
CA3091 
CA3123 
CA3130 
CA3140 
CA3600 
RC4194 
RC4195 



3.75 
10 20 
2 15 



74LSQ0 
74LS02 
74LS03 
74LS04 
74LS05 
74LS08 
7JLS10 
74LS13 
74LS14 
74LS20 
74LS26 
74LS27 
74LS28 
74LS30 
74LS32 
74LS40 
74LS51 
74LS55 
74LS73 



'4 74LSOO TTL 



2i> 



74LS74 

74LS75 

74LS76 

74LS83 

74LS85 

74LS86 

74LS90 

74LS92 

74LS93 

74LS35 

7.1LS96 

74LS107 

74 US 109 

74LS112 

74LS132 

74L5136 

74 LSI 38 



74LS139 

74LS151 

74 LSI 53 

74LS157 

rJLSIQL' 

74LS163 

74LSI64 

74LS175 

74LS131 ■ 

74 IS 190 

74LS19! 

74LS192 

74LS193 

MLS 194 

74LS195 

74LS257 

74LS260 

74LS279 

741S670 



M 
I M 
I - 
I M 

k 



MM5309 
MM5311 
MM5312 
MM5314 
MM5316 
MM5318 
CT7001 



CLOCK CHIPS 

6 Digit. BCD Outputs. Reset PIN. 
6 Digit. BCD Outputs. 12 or 24 Hour 

4 Digit. BCD Outputs. 1 PPS Output 

5 Digit. 12 or 24 Hour, 50 or 60 Hz 
4 Digit. Alarm. 1 PPS Output 

Video Clock Chip. For Use With MM5841 

6 Digit. Calendar. Alarm. 12 or 24 Hour 



4 95 
■1.95 
4.95 

6 y& 

9 95 
5,95 



DATA HANDBOOKS 

7400 Pin out & Description of 5400/7400 ICS $2.95 

CMOS Pin out & Description of 4000 Scries ICS $2.95 

n out & Functional Description $2.95 

ALL THREE HANDBOOKS $6.95 



fairchild TECHNOLOGY KITS fairchild 



TECHwiocY • Complete Specifications on back of each kit 
a k " • Packaged for WALL DISPLAY APPEARANCE 
»■ • Dealer's Inquires Invited — Price List Available 



fcs 



7205 - Stop Watch Chip $19.95 



FTK0001 
FTK0002 
FrK0003 
FTK0004 
FTK0005 



IMIt_Q 

DIGITS 
0.5" High Common Cathode Digit 
0.5" High Common Anode Digit 
.357" High Common Cathode Digit 
8" High Common Calhode Digil 
0.8" High Common Anode Digit 



O.B" HIGH OISPLAY ARRAYS 
12 Hour. 3ft Oigit Clock Display 
24 Hour. 4 Digit Clock Display 



FTK0020 
FTK0021 
FFK0022 
FfK0023 



LED LAMPS 

10 Red LEO Lamps 

5 Mixed Colored LEO Lamps 

10 LEO Mounting Clips 

5 Three Piece LEO Mounting Adapters 



FTK0030 
FTK0031 

FTK0032 
FTK0033 



PHOTO TRANSISTORS 

5 Flat Lens Photo Transistors 
5 Round Lens Photo Transistors 
3 flat Lens Photo Darlingtons 
3 Round Lens Photo Darlingtons 



FTK0040 
FTK0041 
FTK0042 



PHOTO ARRAYS I 
9-Elomem Tape Reader Array 
12-Element Card Reader Array 
Reflective Oplo Coupler 



COUPLERS 

3 General Purpose Opto Couplers 
Darlington Opto Coupler 



FTK0400 
FTK0401 
FrK0402 
FTK0403 
FTK0405 



MOS CLOCK CIRCUITS 
Digital Clock/Calendar Circuit 

(FCM7001) 
Digital Clock/Calendar wilti BCD 

Outputs (FCM7002) 
Direct Drive Digital Clock Circuit 

with AC Output (FCM3817A) 
Direct Orive Digital Clock Circuit 

wilh DC Outpul (FCM3817D) 
Oiiect Oiive Digital Clock/Calendar 

Circuit (FCM7015) 



5 00 
5 DO 



XC209 
XC209 
XC209 



XC22 
XC22 
XC22 
XC22 
SSL-22 



Green 
Orange 



Green 
Yellow 
Orange 



DISCRETE LEOS 



Gieen 

Yellov 



4/S1 

4, SI 



XC526 


Red 


XC526 


Green 


XC526 


Yellow 


XC526 


Crange 


XC526 


Clear 



XC556 
XC555 
XC556 
XC556 
XC556 



Green 
Yellow 
Orange 



Orange 4/S1 

.0B5" dla. 
MV50 

085" dia Micro 
red LED 
6,'SI 



SPECIAL^- XC556 Red 100/S8.00 1000/560.00 — SPECIAL * 

DISPLAY LEOS 



TYPE 

MAN 1 
MAN 2 
MAN 3 
MAN 4 
MAN 7 
MAN 7G 
MAN 7Y 
MAN 52 
MAN 64 
MAN 72 
MAN 74 
MAN 82 
MAN 84 



POLARITY 

Common Anode 
5 x 7 Dot Matrix 
Common Cathode 
Common Calhode 
Common Anode 
Common Anode-green 
Common Anode-yellow 
Common Anode-gfeen 
Common Anode-red 
Common Anode 
Common Cathode 
Common Anode-yellow 
Common Cathode-yellow 



TYPE 

MAN 3620 

MAN 3640 

MAN 4710 

DL701 

DL704 

DL707 

OL 728 

OL747 

DL750 

DL 33B 

FND70 

FND503 

FND507 



POLARITY 

Common Anode-orange 
Common Cathode-orange 
Common Anode-Red 
Common Anode-red ~ 
Common Cathode 
Common Anode 
Common Calhode 
Common Anode 
Common Calhode 
Common Cathode 
Common Cathode 
Common Calhode 
Common Anode 



IC SOLDERTA1L— LOW PROFILE (TIN) SOCKETS 



B pm 
14 pw 

In r,n 



14 pin 
16 pin 
18 pin 
24 pm 



8 pin 
14 pin 
16oin 



35 SOLOERTAIL STANDARD (TIN) 



28 pm 
36 pm 
40 pm 



SOLOERTAIL STANDARD (GOLD) 



43 



36 Din 



75 



WIRE WRAP SOCKETS (GOLD) LEVEL #3 

24 pm 
28 [ii n 
36 pin 
40 pin 



i Plastic Push Button Switch 

* 18 AWG Solid Wire - 5" Long 

* .50 (wide) X .60 (high) tt-27 Thread 

* 8 AMP @ 14 Volt - 1 AMP @ 110 Volt 

1-9 10-Up 
J-188-1 Push On-Push 0(1 .59 .49 
J-188-2 Normally Open .59 .49 

J-188-3 Normally Closed .59 .49 



MINATURE TOGGLE SWITCH 



JMT-221 DPDT on/off/on $1.95 

JMT-223 DPDT on/none/on $1,75 

JMT-121 SPOT on/off/on S1.50 

JMT-123 SPDT on/none/on $1.25 






PLIPLITF ^W LEDMOUNTNG SYSTEM — to be used 

Ul.ll Ll L. wjth XCffi6 LEDS _ ^dPY COLORS - Q/C1 AQ 

♦SPECIAL* RED - GREEN - AM8ER - YELLOW '* " 



50 PCS. RESISTOR ASSORTMENTS $1.75 PER ASST. 



ASST. 1 
ASST. 2 



10 OHM 12 OHM 

27 OHM 33 OHM 

68 OHM 82 OHM 

180 OHM 220 OHM 

470 OHM 560 OHM 



15 OHM 
39 OHM 



18 OHM 
47 OHM 



100 OHM 120 OHM 

270 OHM 330 OHM 

680 OHM 820 OHM 

1 8K 2 2K 



4 7K 



220K 
560K 
1 5M 
3 9M 



5 6K 



270K 
880K 
I SM 



22 OHM 
56 OHM 



2 7K 
6 8K 



120K 
330K 
820K 



1/4 WATT 5% ■ 50PCS. 

1/4 WATT 5%. 50 PCS. 

1/4 WAIT 5% 50 PCS. 

1/4 WATT 5% 50 PCS. 

1/4 WATT 5% 50 PCS. 

1/4 WATT 5% 50 PCS. 

1/4 WAIT 5% 50PCS. 



ASST. 8R Includes Resistor Assortments 1 -7 (350 PCS . ) $10.95 ea. 



$5.00 Minimum Order — U.S. Funds Only 
California Residents — Add 6% Sales Tax 



Spec Sheets • 25c — Send 
Dealer Discount Available - 



24c Stamp tor 1977 Catalog 
- Request Pricing 




1021-A HOWARD AVE., SAN CARLOS, CA. 94070 

PHONE ORDERS WELCOME — (4151 592-8097 

All Advertised Prices Good Thru March 



WIRE WRAP CENTER^ 

HOBBY-WRAP TOOL-BW-630 



"* 



• Battery Operaled (Size C) 
Weighs ONLY 11 Dunces 
Wraps 30 AWG Wire onto 
Standard DIP Sockets (0.25 inch) 
Complete with built-in bit and sleeve 



$34.95 

(Daltcires not included) 

WIRE-WRAP KIT — WK-2-W 

WRAP . STRIP • UNWRAP 

- Tool for 30 AWG Wire 

• Roll of 500 ft. White 30 AWG Wire 

• 50 pes. each 1", 2", 3" & 4" lengths 
pre-stripped white wire 



$11.95 




WIRE WRAP TOOL WSU-30 

WRAP . STRIP . UNWRAP -55.95 



WIRE WRAP WIRE — 30 AWG 

25tt.min.S1.25 50ft.S1.95 100ft. S2.95 1000ft. S15.00 
SPECIFY COLOR — White -Yellow - Red - Green - Blue - Black 



THUMBWHEEL SWITCHES 



THUMBWHEEL SWITCH ON1.V 
P.fi No ; Cw«„p,, on r 

SFT7 .S.r^P,,,,!)^,,,,,,,,-,; 
MS . D«c.m«l 

SF ?1 IDPnut.cmBCDonlv ' ; 
SR 21 1 

SERIES SMrsnlMowMAn^nbl, 



« lit 



sr EP E 

SF OP ' 

SF BB ; B 

SF HB H 



Permacel Electrical Tape 

• % (wide) X 66 rt (long) • Allwealher . Not Import 
$1.49 per roll — $12.50 per 10 roll package 



TYPE 

1N7-16 

1N751A 

1N752 

1N753 

1N754 

1N959 

1N965D 

1N5232 

1N5234 

1M5235 

1N5236 

1N456 

1N458 

1N485A 

1N4001 

1N4002 

1N4003 

ttj.1004 



ZENERS — DIODES — RECTIFIERS 

VOLTS W PRICE TYPE 

1N4005 



3 3 400mm 

5 1 400m 

5 6 400m 

62 400m 

68 400m 

8 2 .100m 

15 O00m 

5 6 500m 

6 2 500m 

6 8 500m 

7 5 500m 
25 40m 
150 7m 
180 10m 

50PIV t AMP 

100 PIV 1 AMP 

200 PIV 1 AMP 

400 PIV 1 AMP 



4/1 00 1N4006 

4/1 00 1N4007 

4/1.00 1N3600 

4,1 00 1N4148 

8 1 00 1N-1154 

4/1 00 1N4305 

28 1N4734 

28 1N4735 

28 1N4736 

28 1N4738 

6 1 00 1N-1742 

6/1 00 1N4/-1: 

6100 IN1183 

12 100 1N1I8J 

12100 1N1185 

12/1 00 1M1166 

12 100 IN1 168 



VOLTS 
600 PIV 1 AMP 
BOO PIV 1 AMP 
1000 PIV 1 AMP 
50 200m 



10m 

10m 



15 1w 

50 PIV 35AMP 
100 PIV 35 AMP 
150 PtV 35 AMP 
200 PIV 35 AMP 
400 PIV 35 AMP 



C36D 
C3BM 
2N2328 
MDA 980-1 
MDA9dO-3 



SCR AND FW BRIDGE RECTIFIERS 

15A@400V SCR 

35A @ 200V SCR 

1 6A@200V 



B50V 
12A@200V 



FW BRIDGE REC 
FW BRIDGE REC 



MPS A05 
MPSA06 
2f!22t9A 
2N2221 
2N2222A 
2N2369 
2N2369A 
FN2415 
2N2W 
2N2906A 
2N2907A 
2N2925 
2N30M 
2N3055 
MJE3055 
MJf.2955 
2N3392 
2N3398 



TRANSISTORS 



5/S1 OC 

5 Si 00 

t;S100 



« 



"'i.vi--.; 

PN3568 
PN3569 

2N370S 
?N3706 
2N3707 
2N371I 
2N372J 
2H3725 
2N3903 
2N390J 
2N3905 
2U3906 

2IK01.1 
2M4123 



!* 



M4 

2N5086 
2N5087 
2rl503B 
2N5089 
2N5129 
2MS138 
2N5I39 
2N5209 
2N5951 



CAPACITOR 



I Opt 

22pf 

47 pi 
100pt 
220 pt 
470p1 

,001mt 

0022 

0047mt 
.01ml 

1/35V 
.15/35V 
.22/35V 
.33/35V 
.47/35V 
.68/35V 
1.0/35V 



47/50V 

1.0/50V .16 

3.3/50V .15 

4.7/25V .16 

10/25V 15 



50 VOLT CERAMIC 
DISC CAPACITORS 

1-9 10-49 50-100 1-9 10-4 

.05 .04 .03 OOVF .05 04 

05 04 03 .0047>iF .05 .04 

05 .04 03 01/,F .05 .04 

05 04 .03 022m F 06 .05 

05 04 03 047^F .06 .05 

.05 .04 .035 .1/iF .12 09 

100 VOLT MYLAR FILM CAPACITORS 

.12 .10 .07 022mf .13 11 

.12 .10 07 .047m! 21 .17 

.12 .10 07 .1ml 27 .23 

.12 .10 07 22ml .33 .27 
+20% DIPPED TANTALUMS (SOLID) CAPACITORS 

,2B .23 .17 1.5/35V .30 26 

28 23 .17 2.2/2SV .31 27 

28 .23 .17 33/25V 31 27 

.28 .23 .17 4.7/25V .32 .28 

28 .23 .17 68/25V .36 .31 

28 23 .17 10/25V .40 35 

.28 .23 .17 15/25V .63 .50 
MINIATURE ALUMINUM ELECTROLYTIC CAPACITORS 
Axial Lead 



CORNER 



13 



10 



10/50V 
22/25V 
22/50V 
47/25V 
47/50V 
100/25V 
100/50V 
220/25V 
220/50V 
470/25V 
1000/16V 
2200/16V 



.47/25V 
47/50V 
1.0/16V 
1.0/25V 
1 0/50V 
4.7/16V 
4.7/25V 
4.7/50V 
10/16V 
10/25V 
10/50V 
47/50V 
100/16V 
100/25V 
100/50V 
220/16V 
470/25V 



Radial Lead 

.13 



r 



^CRYSTALS §r- 



THESE FREQUENCIES ONLY 



Part* 
CY1A 
CY2A 
CY3A 
CY7A 
CY12A 
CY14A 
CY19A 
CY22A 
CY30B 



Frequency 

1.000 MHz 
2.000 MHz 

4 000 MHz 

5 000 MHz 
10.000 MHz 
14.31818 MHz 
18.000 MHz 
20,000 MHz 
32.000 MHz 



Case/Style ~ 

HC33/U 

HC33/U 

HC18/U 

HC18/U 

HC18/U 

HC18U 

HC18/U 

HC18/U 

HC18/U 



-Res 

S5.95 
$5.95 
S4.95 
S4.95 
S4.95 
S4.95 
S4.95 
S4.95 
S4.95 



XR-2260KB Kit S27.95 



WAVEFORM 

GENERATORS 

XR-205 S8.J0 

XR-2206CP J J9 

XR-2207CP 3.85 



XR-2206KA Kit S17.95 



EXAR 



STEREO DECODERS 
XR-13IOCP S3.20 

XR-1310EP 3 20 

XR-1800P 3.20 

XR-2567 2.99 



XR-4136 
XR-1468 
XR-1J88 
XR- 1-189 
XR-2208 



TIMERS 

XR-555CP S j9 

XR-320P 1.55 

XR-556CP 1 85 

XR-2556CP 3.20 

XR-2240CP 325 
PHASE LOCKED LOOPS 

XR-210 5.20 

XR-215 660 

XR-567CP 1-95 

XR-567CT 1.70 



CONNECTORS 

PRINTED CIRCUIT EDGE-CARD 

.156 Spacing-Tin-Double Read-Out 

Bifurcated Contacts — Fits .054 to .070 P.C. Cards 

15/30 PINS (Solder Eyelet) S1.95 

18/36 PINS (Solder Eyelet) S2.49 

22/44 PINS (Solder Eyelet) S2.95 

50/100 1.100 Spacing) PINS (Solder Eyelet) S6.95 

25 PIN-D SUBMINATURE 

DB25 PLUG S3. 25 

DB25 SOCKET S4.95 



3Vz DIGIT DVM KIT 




This 0-2 VDC .05 per cent digital voltmeter features the Motorola 3Vz digit 
DVM chip set. It has a .4" LED display and operates from a single +5V 
power supply. Theunit is provided complete with an injection molded black 
plastic case complete with Bezel. An optional power supply is available 
which fits into the same caseas the 0-2V DVM allowing 1 1 7 VAC operation 

A. 0-2V DVM with Case $49.95 

B. 5V Power Supply $14.95 



VECTOR WIRING PENCIL 

Vector Wrrmg Pencil Pi 73 consists ol a handheld lealherweight (untiei one ounce) 
too) which is used ioguide and wrap insulated wire, fed olt a self-contained leplaceable 
bobbm. onto component leads 01 terminals installed on pie-punched P Paitem 
Vecioibord Connections between Ihe wrapped wiie and campanenl leads oads O; 
leiminais aie made by soldering Complete wilti 250 FT ol red wire tf»Q qc 



REPLACEMENT WIRE — BOBBINS FOR WIRING PENCIL 
W36-3-A-Pkg 3 250 It. 36 AWG GREEN S2.40 

W36-3-B-Pkg. 3 250 ft 36 AWG RED S2.40 

W36-3-C-Pkg 3 250 ft. 36 AWG CLEAR $2.40 

W36-3-[l-Pkg 3 250 It 36 AWG BLUE S2.40 



1/16 VECTOR BOARD 



64P-U 062XXXP 
I69P« 02XXXP 
64P44 062 
SIP-" 062 
169P4-; 062 
I69P8J 062 
I69P-M062C1 



650 
17 00 

6 50 



* 



HEAT SINKS 



y 



205-CB Beryllium Copper Heal Sink with Black riiusn ioiTO-5 S 
291-.36H Aluminum Heal Sink, lor rO-220 transistors & Regulators S ,25 
6B0-.75A Black AnooVed Aluminum $1.60 



HEXADECIMAL ENCODER1 9-KEY PAD 

r ^Q p63 h fc fea fc • ABCDCF 

■kSHCSmE-jm^ • Return Ke y 



MICROPROCESSOR COMPONENTS 



)A CPU 

8212 8 Bit Input/Output 

8216 Bi-Directional Bus Driver 

8224 Clock Generator/Driver 

8228 System Controller - Bus Driver 10.95 



S19.95 MC6800L 8 Bit MPU $35.00 

4.95 MC6820L Periph. Interface Adapter 15.00 

6.95 MC6810AP1 128 x 8 Static RAM 6.00 

10.95 MC6830L7 1024 x 8 Bit ROM 18.00 



2504 
251S 
25'9 
2524 
J52S 
2527 
2529 
2532 
2533 
3341 
74LS670 

AY-5-1013 

2513 

2516 
■4S3S7 



- Key 



$10.95 each 



63 KEY KEYBOARD 




Tins keyboard lealntes 63unen 
coded SPS J" keys u nattactied to 
any kind ol P C fi A very solid 
inolflMl Dlasnc 13 x t base 
sinis mosi aoDliesttons 

$19.95 



HO0165 16 LINE TO FOUR BIT PARALLEL KEYBOARD ENCODER 




JOYSTICK 

These joysticks feature four * 
potentiometers, that vary re- 
sistance proportional to the 
angle of the stick. Sturdy metal 
construction with plastics 
components only at the mova- 
ble joint. Perfect for electronic 
games and instrumentation. 

*5K Pots $6.95 
100K Pots $7.95 



CPUS 

8 BIT CPU 
Super S00B 
Super 8008 

SR'S 
1024 Dynamic 
Hex 32 BIT 
Hex 40 BIT 
512 Dynamic 
i024 Dynamic 
Dual256 BIT 
Dual 512 BIT 
Quad B0BIT 
1024 Sialic 
Frio 
16 x 4 Reg 

UARTS 
30K Baud 

RUM'S 
Char Gen 
Char Gen 
1024 -Bil Proijunnn.ihh' 



S1995 
2-) 95 
19.95 



256 x 1 
t024 x 1 
256x4 



S 9 95 

10 95 



1702A 

5203 
82S23 

52Si?-i 
74S; B 7 
3601 



2048 
2048 

32 * a 
32x8 

1024 
256 x 



RAMS 

Static 
Dynamic 
Sialic 
Static 
Dynamic 
Static 
MNOS 
Static 
Sialic 
Sialic 
Slat 
Sialic 
State 
Sialic . 
Dynamic 
PHOMS 
Fatnos 
Fames 
OpenC 

IrisM!'.' 

Sialic 
Fast 



'Special Programing Available — BIPOLAR PROM SPECIAL — Write or Call lor Pricing' 

256 Bit (32 x 8) Open Collector 
". (32 x 8) Three State 
' > 1 i i n m 



3 40 
9.95 



2-1 



6353-1 



204B Bit (512 x 4) Three Stale 

2048 Bil (512 x 8) Open Collector 

2048 Bil (512 x B) Three Stale 

4096 Bit (102 x 4 Open Collector 

4096 Bit (1024x4) Three State 



9.95 
19.95 

IS S5 
i ■ 
19.95 



Proto Board 100 



Continental Specialties 
$19.95 

ml 






" a - a 79.95 

COMPLETE KIT 



ft* & 



■ 




Proto Board 6 S15.95 



SPECIAL! 



1 



LOGIC MONITOR 

Srniullaneously displays static and 
a* dynamic logic stales of DTL TTL. 
HTL or CMOS DIP ICs 
Pocket size S84.95. 



, QT-50S 
* Q1-59B 



OT PtolO Slnps 



-■m^mmi^r- 



' ■ 



Ut-b9l 

01 -1,-S 
OT.17IJ 



GEMINI -68 The Unique Microprocessing System 




ALL BOARDS BUS EXPANDABLE 

Uses standard size AV2" wide boards, dual 22 pin edge connector 
Fully buffered and tristatable address and data buses 

STAND ALONE CPU BOARD — Has384 bytes of RAM on board, serial I/O (RS-232 

and 20 ma current loop, cycle stealing direct memory access (DMA), built in soft- ^ _ n n _ 

ware — selectable echo-back capability. Pari # SA-CPU Board $279.95 

CPU BOARD — Same as above but only has 128 bytes ot RAM on board-used with -, ocn nc 
8K RAM board listed below Part # Gemini 68 CPU Board $259.95 

8K RAM BOARD — Uses low power static RAMS, 500ns cycle time, 1.5 Amps Max ^ _ _ _ _ 

Part # Gemini 68 RAM Board $269-95 

8K EPROM BOARD — Uses 5204 EPROMS by AMI or NATIONAL. Shipped with all 
decode and miscellaneous ICs. except the 5204 EPROMS -, __ __ 

Part # Gemini 68 EPROM Board $ 89-95 

NOT A KIT — ALL BOARDS ARE COMPLETELY ASSEMBLED, 
BURNED-IN AND TESTED. COMES WITH COMPLETE DOCUMENTATION. 

Allow appioxmiaielytour weeks loi delivery 



$5.00 Minimum Order — U.S. Funds Only 
California Residenls — Add 6% Sales Tax 



Spec Sheets - 25c — Send 24c Stamp for 1977 Catalog 
Dealer Discount Available — Request Pricing 




1021-A HOWARD AVE., SAN CARLOS, CA. 94070 

PHONE ORDERS WELCOME — (415) 592-8097 

All Advertised Prices Good Thru March 



DIP SWITCH 



n spst sime switches m a 
1 smted for microprocessor 

SI.95 



CD Timebcind '" 

DIGITAL ALARM CLOCK $16.95 



i 24-Hour Alarm 

i "DOZE" Button 

i 100% Solid State 

i Large Red Led Display (.8" high) 

1 AM/PM Indicator 
Seconds Display at touch of button 
SPECIFY BLACK OR IVORY 




DIGITAL WATCHES 




$59.95 



EXELAR Mens Watch 

• 5 Function 

• Quart? Crystal 

• Black Leather Band 

• Manufacturer Guarantee 

• Specify Gold 
or Chrome 

$25.00 



5 FUNCTION ELECTRONIC CALCULATOR 
RADOFIN MODEL 8P 



$8.95 



• B Digit Dsplay 

• 5 Funciionsconsstsoiafldilion subtraction , mul- 
tiolicatlon drviSion percentage with constant on 
all functions, with tull floating decimal point 

• Power source is 1 piece 9V DC BatteiyOOGP. 
lack for AC adaoter 

• Black superfine grained I 



iem piasiic cabinet 




DIGITAL STOPWATCH 



• Bright 6 Digit LED Display 

• Times to59 minutes 59 59 seconds 

• Crystal Controlled Time Base 

• Three Stopwaiches in One 

Times Single Event — Sphl & Taylor 

• Size 4.5 x 2 15 "x 90" 141i ounces) 

• Uses 3 PenliteCells. 

Kit- $39.95 

Assembled — $49.95 

Heavy Duty Carry Case $5.95 




DIGITAL DUARTZ CAR CLOCK 




Kit: $29.95 
Assembled: $39.95 



Complete kit irom mounting bracket ol the 
injection molded case down to Ihe Ihree con- 
ductor power cord and all component in- 
cluding MM53M clock chip Featuies quart: 
accuracy ol 01% six digit 35' high LED 
display, and P C Boaids Works on any 12 
voli system — molar cycles boais. vans 
motoiiiomes aulos and trucks 

DIMENSIONS .IV x J » 2 
12 01 2-1 HOUR MODE 



CASE ONLY (includes hardware, mounting bracket and bezel) $5.95 




115 VAC 



JE700 CLOCK 

The JE'OO is a low cost digital clock, but 
ts a very high quality unit. The unit lea- 
lures j simulated walnut case with di- 
mensions ol 6 x2'? *i It utilizes a 

MAN 72 high tuightness readout, and the 

t.\mV-\ clock chip 

$17.95 



yd'.H 9 3* 



This large digit dock (.6 hours & 
minutes. .3" seconds)features the 
MM5314 clock chip tl operates 
Irom 117 VAC. and will operate in 
either a 1 2 or 24 hour mode The 
clock is complete with a walnut 
grain case, and has fast set, slow 
set. and hold time set features. 

JE500 KIT - ALL COMPONENTS & CASE $34.95 
WIRED & ASSEMBLED S39.95 



DIGITAL CLOCK KIT — 3 1 / 2 INCH DIGITS 



4 DIGIT KIT $49.95 
6 DIGIT KIT S69.95 



4 DIGIT ASSEMBLED $59.95 
6 DIGIT ASSEMBLED $79.95 



This clock features big 3Vz" high digitsfor viewing in offices. auditoriums, 
etc. Each digit is formed by 31 bright 0.2" LED's. The clock operates from 
11 7VAC, has either 12 or 24 hr. operation. The 6 digit version is 27" x 
3V2' x IV2" and the 4 digit is 18" x 3 1 /?" x HV'.Kils come complete with 
all components, case and transformer. 

Specify 12 or 24 Hour When Ordering 



JE803 PROBE 



The Logic Probe is a uml which is lor the most part , 

mdespensibie in trouble shooting logic families +^ 

TTL DTL RTL CMOS II denves the power i|- ■^-™ t= ^ 1 p>~,3 
needs lo operate directly of! ot me circutl under — 

est. drawing a scanl 10 rrtA ma* II uses a MAN3 
•eadoul to indicate any ol the following slates Qy 
these symbols iH)- 11 LOW) 01 PULSE) P Ri« 
Probe can del eci niqh frequency pulses to 45 MH/ 
it can t be used at MOS levels 01 circuit damage 
will result 






$9.95 Per Kit 

printed circuit board 




PL5V1A Supply 

This isa standaid TTL powei supply using the well known 
LM309K regulator IC lo piovideasolid 1 AMPol currentat 5 
voils We li-y lo make things easy tor you by provrdmg 
everything you need in one package, including ihehardware 

,orm,ly $9.95 Per Kit J 






SPECTRA FLAT TWIST 

50 conductor, 28 gauge, 7 strands/conductor 
made by Spectra. Two conductors are paired & 
twisted and the flat ribbon made up of 25 pairs 
to give total of 50 conductors. May be peeled 
off in pairs if desired. Made twisted to cut 
down on "crosstalk." Ideal for sandwiching PC 
boards allowing flexibility and working on both 
sides of the boards. Cost originally $ 1 2.00/ft. 



SP-234-A $1.00 ft 50 cond. 1 ft/$9.00 
SP-234-B .90 ft 32 cond. 10ft/$8.00 




WIRE WRAP WIRE 

TEFZEL blue #30 Reg. price $13.28/100 ft. Our 
price 1 00 ft. $2.00; 500 ft. $7.50. 



MULTI COLORED SPECTRA WIRE 



Footage 
8 Cond. 

12 " 

14 " 

29 " 



#24 
22 
22 
22 



10' 
$2.50 
3.00 
3.50 



50' 

9.00 

11.00 

13.00 



100' 
15.00 
18.00 
21.00 



7.50 28.00 45.00 



Great savings as these are about 1/4 book prices. 
All fresh & new. 



VIATRON cassette tape deck as shown $35.00 

Set of 2 read/write, amplifiers & servo control boards for deck $40.00 

VIATRON full spare set of 11 microprocessor boards, checked out $200.00 

COM ADAPTER kit RS-232C will run any baud rate 110-1200 BPS. TTL logic and UART 

w/diagram, control panel for Viatrbn & cable $90.00 

COM ADAPTER as above fully assembled & tested, panel, cables $1 50.00 

VIATRON large tape deck, 7 bit ascii, 9 track, 800 BPI w/powersupply cables, control panel, 

tape, instructions $375.00 





AM-FM solid state w/power supply for 115 volts AC. Has mike input, 
stereo tape or record player input, built-in loop stick. Ready to use, just 
add speakers $1 0.00 




CREDIT VALIDATER 

Made for feeding into a computer terminal to query the credit balance of a customer 
with push-button entry and audio response. Power supply in separate case attached 
to base may be removed to use for other projects should you wish to scrap. Regular 
115 volt input and output of plus 5 volts and plus & minus 12 V both DC & 
regulated. The phone is touch pad style, automatic electric pad. All sold "as is" 2 PC 
boards inside jammed with various parts & ICs including memory. Uses buffers ICs to 
accelerate & decelerate call traffic. Inquiry from Validier emerge as short bursts of 
Binary data signals. Normally used over leased phone lines at 200 times the capacity 
of messages. All appear to be excellent & complete. A Computer gadgeteers 
SPECTACULAR. And at a crazy price of only $1 8.00. 2 for $35.00 

Ship. wgt. 101b. #SP-153-AL ea $18.00 



PARITY DETECTOR 

New packaged, made for RCA, detects even or odd 
parity, baud rate 110, 150 or 134.46. Built-in logic 
supply for the ICs, operates from standard 115 Vac. 
Control panel allows manual or automatic reset mode 
of operation. Aluminum enclosure (not shown) covers 
the electronics. TTY compatible. Ship wt 10 lbs.$12.50 




l*0tQ&& 



Please add shipping cost'on above. 

FREE CATALOG SP-9 NOW READY 

P.O. Box 62, E. Lynn, Massachusetts 01904 






The prokoboard 
from BIM... 

$14 

2/$25 




4/$44 




TOP QUALITY 



$28 



HEAVY 

DUTY 

POWER 

TRANSFORMER 

FOR 

IMSAI/ALTAIR 




5VDC 

@ 22A 



Check or money order 
only. Calif, residents 6% 
tax. All orders postpaid 
in the U.S. $10 Min. 
order. Prices subject to 
change without notice. 



#18 VDC 

40V 

(Prom programming)! 

INCLUDE APPROX SHIPPING 

the proko 
electronics shoppe 

439marsh st. 
san luis obispo, ca. 93401 
805/544-5441 



«8 



■eiectrontcs 




The Proko Paper Tape Reader: A manually operated reader, reads 9-level paper tape into 
any parallel input port. Just supply a light source, grab the tape and pull! 

KIT $42 Assemb. $55 



EDGE CONNECTORS 

80 Pin WW .125" used $1.50 ea. 10/12.50 

86 Pin Soldertail .156" $3.75 ea. 10/$32 

100 Pin spec WW or Soldertail both fit IMSAI or SSM 

Mother Bd $5.00 ea 10/$44 



I. 



KITS BY CYBERCOM A DIVISION OF SOLID STATE MUSIC 



I I 

I MEM M^-SboarTl'usec 2l02or eq. PC Board $22 1 6 

!Kit $83 



I 32 x 16 or 64 x 16 switch selectable. Composite and 
■ parallel video ports, upper and lower case with software. 



JMB-2 Altair 8800 or IMSAI compatible Switched address j Kit $1 79.95 

■ and wait cycles. PC Board $25 ■ 



82S06 
82S07 
82S11 
82S12 
82S17 
82S23 
82S123 

7400 
7401 
7402 
7403 
7*404 
7405 
7406 
7407 
7408 
7409 
7410 
7411 
7413 
7414 
7416 
7417 
7420 
7423 
7425 
7426 
7427 
7430 
7432 
7437 
7438 
7440 
7441 
7442 
7443 
7444 
7445 
7446 
7447 
7448 
7450 
7451 
7453 
7454 
7460 
7470 
7472 



2.00 82S126 

2.00 82S129 

2.00 82S130 

2.00 82S131 

2.00 74S206 

2.50 74S412 

3.00 74S301 



.16 7473 

.16 7474 

.21 7475 

.16 7476 

.18 7480 

.24 7483 

.20 7485 

.29 7486 

.25 7489 

.25 7490 

.18 7491 

.30 7492 

.45 7493 

.70 7494 

35 7495 

35 7496 

.20 74100 

.37 74107 

.30 74109 

.30 74121 

.35 74122 

.25 74123 

.30 74125 

.27 74126 

.27 74132 

.15 74141 

.85 74145 

.60 74147 

.75 74148 

.75 74150 

.75 74151 

.80 74153 

•70 74154 

.80 74155 

.25 74156 

.25 74157 

•25 74160 

20 74161 

.20 74162 

.45 74163 
.40 



74C200 

8573 

8574 

8575 

8576 

8577 

8578 

74164 

74165 

74166 

74170 

74173 

74174 

74175 

74176 

74177 

74179 

74180 

74181 

74182 

74184 

74185 

74190 

74191 

74192 

74193 

74194 

74195 

74196 

74197 

74198 

74199 

74200 

74251 

74284 

74285 

74365 

74367 

74368 

MH0025 

MH0026 

95H90 

2102-1 

32 

64 

1488 

1489 



ft ■! Kit (91L02A .5 usee).... $129.95 

J MB-4 Improved MB-2 designed for 8K "piggy-back" { ^'^ 

1 without cutting traces. PC Board $30 

1 Kit 4K .5 usee $129.95 Kit 8K .5 usee $199 



Altair compatable mother board. Room for 15 connec- 
tors 11" x 11V&" (w/o connectors)....*. $45 
| With 15 connectors $111.00 

I MB-3 1702A's Eroms, Altair 8800 & Imsai 8080compat-, Ali , , 

■ ible Switched address & wait cycles. 2K may be ex- ™ e * tender b ° ard < w '° -connectors).... 

Jpanded to 4K. Kit less Proms $65 2K Kit $145 W.th w/w connector $13.50 

| 4K Kit $225 j 

I MB-6A 8Kx8 Switched address and wait assignments! 
I Memory protection is switchabie for 256, 512, 1K, 2K, 4K I 
land 8K. 91L02A .5 usee rams, Altair 8800 & IMSAI I 
l| compatible. With battery power option 
iKit $250 Assembled & tested $290 



MODEMS 

1702A*EROM 

1702A* 2 usee 

'programming send hex list 
I AY5-1013UART 
I 2513 prime spec, upper or 



$85.00 

$10.00 

8.00 

5.00 I 

$6.95 



■ l/O Boards ■ lowercase 

1:170-2170 for 8800, 2 ports, committed pads for 3 more, ' ?°?° A P nm f CP }i tt 

| 8212pnme latch buffer 

j 8224primeclockgen 

■ 8228primesys controller 



Jother pads for EROMS UART, etc. 

■Kit $47.50 PC Board only $25 

r 

| MM1402A 
■ MM1404A 
I MM5006A 

B i 



11.00 

25.00 

4.00 

5.00 

8.90' || 



I 



MM5013 
MM5015A 

■ MM5016 
I MM5017 
I MM5025 
| MM5026 
| MM5027 
| MM 5053 

■ MM 5054 

■ MM5055 
J MM5056 
J MM5057 

■ MM5058 
J MM5314 

■ MM5316 
1 MM5320 
I MM5554 
I MM5555 
I MM5556 

I 



1101 1.25 

1103 1.25 

2101 4.50 

2102-1 1.65 

2111-1 4.50 

2112 4.50 

2602 1.60 

4002-1 7.50 

4002-2 7.50 

MM5260 1.00 

MM5261 1.00 

MM5262 1.00 

7489 2.00 

74200 4.95- 

74S89 3.50 

74C89 3.50 

74L89 3.50 

8223 2.50 

F4702 17.00 
(baud rate gen) 
2.4576 MHZ 

Crystal 8.95 



74LS00 

74LS01 

74LS02 

74LS03 

74LS04 

74LS05 

74LS10 

74LS11 

74LS12 

74LS20 

74LS22 

74LS27 

74LS30 

74LS42 

74LS55 

74LS73 

74LS74 

74LS76 

74LS151 

74LS174 

74LS175 

74LS192 



74L78 

74L85 

74L86 

74L89 

74L90 

74L91 

74L93 

74L95 

74L98 

74L123 

74L154 

74L164 

74L165 

74L192 

74L193 

MC4044 

N8264 

N8263 

N8826 

DM8131 

8T37 

8T10 



90 Day Guarantee on SSM Products. Kits MB-2, MB-3 
(2K OR 4K), MB-4, MB-6, 10-2 video board and mother 
board with connectors may be combined for a discount of 
10% in quantities of 1 or more. This supercedes the flier 
of 13 Sept. 1976. 



MIKOS 

419 Portofino Dr. 
San Carlos, Ca. 94070 

Please send for xtstor. JC & kit list 



For large orders please send money order or cash- 
iers check to avoid delays in waiting for checks to 
clear. 

Check or money order only. Calif, resident 6%tax. 
All orders postpaid in U.S. All devices tested prior to 
sale. Money back 30 day guarantee. Sorry we can 
notacceptreturnedlC'sthathavebeensolderedto. 
$10 min. order. Prices subject to change without 
notice. 



Thinly disguised affiliates of KO Electronics and Surplus, S.L.O., CA 93401 






S.D. SALES CO. 



Z-80 CPU CARD KIT 
FOR IMSAI/ALTAIR 



P.O. BOX 28810 - B 
DALLAS, TEXAS 75228 



From the same people who brought you the $89.95 4K RAM kit. We were not the first to 
introduce an IMSAI/ALTAIR compatible Z — 80 card, but we do feel that ours has the best 
design and quality at the lowest price. 

The advanced features of the Z— 80 such as an expanded set of 158 Instructions, 8080A 
software compatibility, and operation from a single 5VDC supply, are all well known. What 
makes our card different Is the extra care we took In the hardware design. The CPU card will 
always stop on an Ml state. We also generate TRUE SYNC on card, to Insure that the rest of 
your system functions properly. Dynamic memory refresh and NMI are brought out for your 
use. Believe It or not, not all of our competitors have gone to the extra trouble of doing this. 

As always, this kit Includes all parts, all sockets, and complete Instructions for ease of assem- 
bly. Because of our past experience with our 4K kit we suggest that you order early. All orders 
will be shipped on a strict first come basis. Dealers Inquiries welcome on this Item. 

Kit shipped with 2 MHZ crystals for existing 500NS memory. Easily modified for faster RAM chips when the prices 

come down. Z-80 Manual - $7.50 Separately. 

Kit includes Zilog Manual and all parts. 



$149: 



JUMBO 
LED 
CAR 

CLOCK 



$16.95 

KIT 



You requested it! Our first DC operated clock kit. 
Professionally engineered from scratch to be a DC 
operated clock. Not a makeshift kluge as sold by others. 
Features: Bowmar 4 digit .5 inch LED array, Mostek 
50252 super clock chip, on board precision time base, 
12 or 24 hour real time format, perfect for cars, boats, 
vans, etc. Kit contains PC Board and all other parts 
needed (except case). 50,000 satisfied clock kit cus- 
tomers cannot be wrong! 

FOR ALARM OPTION ADD $1.50 
FOR XFMR FOR AC OPERATION ADD $1.50 



60 HZ CRYSTAL TIME BASE FOR DIGITAL CLOCKS 

S.D. SALES EXCLUSIVE! 
KIT FEATURES: 

A. 60HZ output with accuracy comparable to a digital watch. 

B. Directly interfaces with all MOS Clock Chips. ^ 

C. Super low power consumption. (1 .5 ma typ.) $5.95 Or 

D. Uses latest MOS 17 stage divider IC. 2/$10. 

E. Eliminates forever the problem of AC line glitches. 

F. Perfect for cars, boats, campers, or even for portable clocks 
at ham field days. 

G. Small Size, can be used in existing enclosures. 

KIT INCLUDES CRYSTAL, DIVIDER IC, PC BOARD 
PLUS ALL OTHER NECESSARY PARTS & SPECS 



50HZ CRYSTAL TIME BASE KIT - $6.95 
All the features of our 60HZ kit but has 50HZ output. For use 
with clock chips like the 50252 that require 50HZ to give 24 
hour time format. 






THIS MONTH'S SPEC! A LS! 

300.00 KHZ CRYSTAL - $1.50 

8080A - CPU CHIP by AMD - $19.95 

82S1 29 - 256 x 4 PROM - $2.50 

N.S. 8865 OCTAL DARLINGTON DRIVERS 

3 for $1 .00 

Z-80 - CPU by Zl LOG - $69.95 

MM5204 - 4K EPROM - $7.95 

Prices in effect this month ONL Y! 






4K LOW POWER RAM BOARD KIT 
THE WHOLE WORKS - $89.95 

Imsai and Altair 8080 plug in compatible. Uses low power 
static 21 L02-1 500ns. RAM's, which are included. Fully buffer- 
ed, drastically reduced power consumption, on board regulated, 
all sockets and parts included. Premium quality plated thru 
PC Board. 



7400-- 19c 
74LS00— 49c 
7402— 19c 
74LS02— 49c 
7404— 19c 
74L04— 29c 
74S04— 44c 
74LS04-49C 
7406— 29c 
7408— 19c 
7410— 19c 



7411— 29c 
7413— 50c 
7416— 69c 
7420— 19c 
7430— 19c 
7432— 34c 
7437— 39c 
7438— 39c 
7440— 19c 
7447— 85c 
7448— 85c 



7451 — 19c 
7453 — 19c 
7473— 39c 
7474— 35c 
74LS74-59C 
7475— 69c 
7476— 35c 
7480— 49c 
7483— 95c 
7485— 95c 
7486— 45c 



TTL INTEGRATED CIRCUITS 



7490— 65c 
74LS90— 95c 
7492— 75c 
7493— 69c 
7495— 75c 
7496— 89c 
74121-38C 

7 412365 c 
74132-1.70 
74S138-1.95 
74141-75C 



74153- 
74154 
74157 
74161 
74164 
74165 
74174 
7481 
74191 
74192 
74193 
74195 



-75c 
1.00 
-75c 
-95c 
1.10 
1.10 
—95c 
2.50 
1.25 
1.25 
■1.00 
-69c 



STICK IT! 

in your clock 

in your DVM, etc.! 



Huge Special Purchase 

Not Factory Seconds 

As sold by others! 



$3.95 



i d • U LI 



r°^^^w^ ) 



4 JUMBO .50" 

DIGITS ON 

ONE STICK! 

(with colons and 

AM/PM Indicator) BUY 3 for $1 0. 

BOWMAR 4 DIGIT LED READOUT ARRAY 

The Bowmar Opto-Stick. The best readout bargain we have ever 
offered. Has four common cathode jumbo digits with all seg- 
ments and cathodes brought out. Increased versatility since any 
of the digits may be used independently to fit your applications. 
Perfect for any clock chip, especially direct drive units like 
50380 or 7010. Also use in freq. counters, DVM's, etc. For 12 
or 24 hour format. 



UP YOUR COMPUTER! 

21L02-1 1K LOW POWER 500 NS STATIC RAM 

TIME IS OF THE ESSENCE! 

And so is power. Not only are our RAM'S faster than a speeding 
bullet but they are now very low power. We are pleased to offer 
prime new 21 L02— 1 low power and super fast RAM's. Allows 
you to STRETCH your power supply farther and at the same 
time keep the wait light off. 8 for $12.95 



<fcl?QR S.D. SALES EXCLUSIVE! ^1?QR 

Wit-.vu MOS 6 DIGIT UP-DOWN COUNTER *J>i*-.^ 

40 PIN DIP. Everything you ever wanted in a counter chip. 
Features: Direct LED segment drive, single power supply (12 
VDC TYP.), six decades up/down, pre-loadable counter, sep- 
arate pre-loadable compare register with compare output, 
BCD AND seven segment outputs, internal scan oscillator, 
CMOS compatible, leading zero blanking. 1MHZ. count input 
frequency. Very limited qty. WITH DATA SHEET 



WESTERN DIGITAL UART 

No. TR1602B. 40 pin DIP 

This is a very powerful and 

popular part. 

NEW-$6.95 with data 

LIMITED QUANTITY 



RESISTOR 
ASSORTMENT 

% W 5% and 10% 

PC leads. A good mix 

of values. 200/$2. 



1702A 2K ERASEABLE 
PROM'S - $6.95 

We tell It like It is. We could 
have said these were factory 
new, but here is the straight 
scoop. We bought a load of 
new computer gear that con- 
tained a quantity of 1702 A's 
In sockets. We carefully re- 
moved the parts, verified their 
quality, and are offering them 
on one heck of a deal. First 
come, first served. Satisfaction 
guaranteed! U.V. Eraseable. 
$6.95 each 4 for $25 



TERMS: 
Money Back Guarantee. No 
COD. Texas Residents add 5% 
tax. Add 5% of order for 
postage and handling. Orders 
under $10. add 75c. Foreign 
orders: US Funds ONLY! 



SLIDE SWITCH 
ASSORTMENT 

Our best seller. Includes 
miniature and standard 
sizes, single and multi- 
position units. All new, 
first quality, name 
brand. Try one package 
and you'll reorder 
more. SPECIAL 12/$1. 



MOTOROLA POWER 
DARLINGTON 
Back in Stock! 

Like MJ3001. NPN 80V. 1 0A. 
HFE 6000 TYP. TO-3 case. 
We include a free 723C volt 
reg. with schematic for power 
supply. SPECIAL — $1.99 



CALL YOUR BANK 

AMERICARD OR MASTER 
CHARGE ORDER IN ON 
OUR CONTINENTAL 

UNITED STATES TOLL 
FREE WATTS: 

1-800-527-3460 

Texas Residents Call Collect 

214/271-0022 



S.D. SALES CO. 
P.O. BOX 28810 B 
Dallas, Texas 75228 



For orders over $15.00 Choose $1.00 FREE rrjdse. 



F8 EVALUATION BOARD KIT WITH EXPANSION CAPABILITIES 



A fantastic bargain for only 



• 20 ma of RS 232 interface 

• 64K addressing range 

• Program control timers 

• 1K off on board static memory 



$99 



with the following features: 

00 • Built in clock generator 

• 64 Byte register 

• Built-in priority interrupts 

• Documentation 



GENERAL PURPOSE COMPUTER POWER SUPPLY KIT 



This power suppy kit features a high frequency torroid transformer 
with switching transistors in order to save space and weight. 
1 1 5V 60 cycle primary. The outputs with local regulators are + 5V 
at 10A, -5Vat 1A, ± 12V at 1A. 



$79 



00 



$74 



UNIVERSAL 4K X 8 MEMORY BOARD KIT 



This memoryboard kit can be used with most microcomputers. 
cq Some of the outstanding features are: 

32-2102-1 static RAM's, 16 address lines, 8 data lines in, 8 data 
lines out, all buffered. On board decoding for any 4 of 64 pages. 



4K F8 Basic $25.00 



2708-PROM . S55.00 

2522 STATIC SHIFT REG S1.95 

2518-HEX 32BITSR S3.50 

2102-1 1024 BT RAM S1.80 

5280 4K DYNAMIC RAM S10.50 

5202AUV PROM S10.50 

MM5203UV PROM S10.50 

1702A UV PROM S10.75 

5204-4K PROM . S18.95 

MINIATURE MULTI-TURN TRIM POTS 
100. 500. 2K, 10K, 100K, 200K, 1 Meg. 

S.75each 3/S2.00 

MULTI-TURN TRIM POTS Similar to Bourns 
301 style 3/16"x5/8"x1 -1 /4"; 50, 100, 
1K. 10K.50K ohms 

Sl.SOea _ .3/S4.00 

LIGHT ACTIVATED SCHs 

TO-18, 200V 1A. S 1.75 

TRANSISTOR SPECIALS 

2N3585 NPN SiTO-66 S .95 

2N3772 NPN Si TO-3 S 1 .60 

2N4908 PNP Si TO 3 S 1.00 

2N6056 NPN Si TO-3 Dnr!inijion S 1.70 

2N5086 PNP Si TO-92 4/S 1 .00 

2N4898 PNP TO 66 S .60 

2N404 PNP GE TO-5 5/S 1 .00 

2N3919 NPN Si TO-3 RF S 1 .50 

MPSA 1 3 NPN Si TO-92 3/S 1 .00 

2N3767 NPN Si TO-66 . S .70 

2N2222 NPN Si TO-18 5/S 1 .00 

2N3055 NPN Si TO-3 S .80 

2N3904 NPN Si TO-92 5/S 1 .00 

2N3906 PNP Si TO-92 5/S 1 .00 

2M5296 NPN Si TO-220 S .50 

2N6109 PNP Si TO-220 S .55 

2N3638 PNP Si TO-5 5/S 1 .00 

2N65I 7 NPN TO-92 Si 3/S 1 .00 

C/MOS (DIODE CLAMPED) 

74C02- .22 4015- .95 4035-1.10 

74C10- .22 4016- .40 4042- .78 

74C193 1.50 4017-1,05 4047-2.00 

4001- .22 4018-1.00 4049- .40 

4002- .22 4019- .25 4050- .40 
4006-1.20 4022- .95 4055-1.50 
4007- .22 4024- .75 40G6- .80 

4009- .42 4027- .40 4071- .22 

4010- .42 4028- .88 4076- .70 

4011- .22 4029-1.10 4081- .22 

4012- .22 4030- .22 4520-1.15 

4013- .40 

M C A -8 1 O PT I C A L L I M 1 1 S W ITCH. S 1 . 50 

LED READOUTS 

FND 500-.5" C.C $1.75 

HP 7740-.3" C.C. . SI. 40 

MAN-7-.3" C.A S1.25 

NS 33-3 din. array Si. 35 

PL 747 . . . S2.50 

Send 2bi for our catalog featuring 
Transistors and Rectifiers 



PRINTED CIRCUIT BOARD 



7WATTLD-65LASER DIODE IB $a95 



2N3820P FET $ .45 

2N 5457 N FET $ .45 

TIS 43 UJT % .35 

ER 900TRIGGER DIODES .. 4/ $1.00 

2N6028PROG. UJT $ .65 

8 PIN DIP SOCKETS $ .24 

14 PIN DIP SOCKETS S .25 

1G PIN DIP SOCKETS $ .23 

18 PIN DIP SOCKETS S .30 

24 PIN DIP SOCKETS . $ .40 

40 PIN DIP SOCKETS S .60 

VERIPAX PC BOARD 
This board is a 1/16"sinyle sided paper epoxy 
bonrd, 4'/'"x6!i" DRILLED and ETCHED 
which will hold up to 21 simile 14 pin IC's 
or 8, 16, or LSI DIP IC's wilh Lnusses for 
power supply connector S4.QQ 



TANTULUM CAPACITORS 



Full Wave Bridges 



. S125 
. S .50 



MV 5691 YELLOW-GREEN 

BIPOLAR LED 

FP 100 PHOTO TRANS .... 
RED, YELLOW, GREEN OR 

AMBER LARGE LED's . . . e;., S .20 

MOLEX PINS 100/S1.00 

1000/S7.50 
10 WATT ZENERS 3.9, 4.7, 5.6, 8.2, 12, i5, 

18, 22, 100, 1 50 or 200V . . . c;i. S .60 
1 WATT ZENERS 4.7, 5.6, 10, 12, 15, 

18 OR 22V en. S .25 

MC68Gt MODEM CHIP S13.00 



SILICON SOLAR CELLS 



214" diameter 



.4V at 500 ma. 



REGULATED MODULAR 
POWER SUPPLIES 

+ -15 VDC AT lOOma 

115VAC INPUT S27.95 

5VDC AT 1 A. 11 5VAC INPUT . . . S24.95 

12 VDC AT .5 AMP S24.95 

IN 4148 (IN914) 15/S1.0U 



.ld\jv jbv b.bl.00 
4 7UF 35V 5/S 1.00 
.GBUF 35V 5/S 1. 00 
1UF 35V 5/S i. on 
2.2UF 20V 5/S 1.00 
3.3UF 35V 4/S1.00 



6.SUF 35V 3 '$1.00 
22UF 35V $ 40 
33UF 35V S 40 
30UF GV 5/S 1.00 
lOniJF 35V £ .50 
150UF 15V $ .50 



M7001 ALARM CLOCK CHIP 



Sij./l, 



NATIONAL MOS DEVICES 1 



MM1402 
MM1403- 
MM1404 
MM5013 
MM5016- 
MM5017- 
MM5055- 
MM5056 



2.50 
2.70 



MM5057- 2.25| 
MM5058-2.75 
MM5060- 2.751 
MM5061- 2.50 J 
MM5555- 4 
MM5556- 4 
MM5210- 1 
MM5260- 1 



#30 WIRE 
WRAP WIRE 
SINGLE 
STRAND 
100 FT. 
ST. 40 





Silicon Power Rectifiers 




PRV 


1A 


3A 


12A 


50 A 


125A 




100 


.06 


.14 


.30 


.80 


3.70" 




200 
400 


.0 7 
.09 


.20 
.25 


.35 
.50 


1.15 
1.40 


4.25 , 
6.50 




G0U 
800 _ 
1000 


.11 

.15 
.20 


.30 


.70 


1.80 


8.50 




.35 
.45 


.90 
1.10 


2.30 
2.75 


_io.50 

12.50 



.$4.00ea.,6/$22.50 



7400- 

7401- 

7402- 

7403- 

7404- 

7405- 

7406- 

7407- 

7408- 

7409- 

7410- 

7411- 

7412- 

7413- 

7414- 

7416- 

7417- 

7420- 

7425 

7426- 

7427- 

7430- 

7432- 

7437- 

7438- 

7440- 

.7441 - 



TTLIC 

7442- 
7445- 
7446- 
7447- 
7448- 
7450- 
7472- 
7473- 
7474- 
7475- 
7476- 
7480- 
7483- 
7485- 
7486- 
7489 
7490- 
7491- 
7492- 
7493- 
7494- 
7495- 
7496- 
74107- 
74121- 
74123- 
74125- 



SERIES 

.52 74126- 



74155- 
74157- 
74161- 
74164- 
74165 
74173- 
74174- 
74175- 
7417 7- 
74180 
74181- 
74190- 
74191- 
74192- 
74193- 
74194- 
74195- 
74196 



1.05 
1.40 
.95 
.92 
.79 
.70 



.40 



74257 
74279 
75324 
75491 
75492 



MINIATURE DIP SWITCHES 
CTS 206-4 Four SPST switches 

in one minidip package. . . Si. 75 
CTS-206-8 Eight SPST switches in a 16 

pin DIP package. .... S1 g5 



AY-5-1013-A30K ser./par., par./ser., uni- 
versal UART S6.95 



=x.LCOMINIATURE TOGGLE SWITCHES 
MTA 106SPDT S1 .20 



PRV 2A 6A 25A 

200 1 7j3 1.25 2.00 

400 j)!5 1.50 3.00 

600 1.20 1_7E> 4.0Q 

SANKEN AUDIO POWER AMPS 

Si 1 010 G 10 WATTS $ 7.95 

Si 1020 G 20 WATTS S15.95 

Si 1050 G 50 WATTS $27.95 

CCD 1 10 LINEAR 256 XI BITSELF 
SCANNING CHARGED COUPLED 

DEVICE S99.00 

CCD 201 ■- 100 x 100 CHARGE 
COUPLED DEVICE S135.00 

LINEAR CIRCUITS 

LM307 Op. Amp S .30 

LM309K 5V 1 A REGULATOR .. S .95 

723 - 40 + 40VV REGULATOR . . S .50 

301 /748-Hi Per. Op. Amp S .31 

320T 5,12.15, oi 24V NEG REG . . S1.25 

709C OP. Ami) 3 .31 

741 A or 741C OP AMP S .31 

710 COMPARATOR S .35 

CA 3047 Hi PeL Op. Amp S .95 

340T 5, 6, 8,12,15,1 8, 24V POS 

REG. TO-220 . . . SI. 10 

1.01 OPER. AMP. HI PERFORM. . , S 75 

LM 308 Oper. Amp., Low Power . . S .95 

747 -DUAL 741 S .65 

556 - DUAL TIMER SI. 00 

537 - PRECISION OP. AMP Si 70 

LM 3900 - QUAD OP. AMP .... S 49 

LM 324 - QUAD 741 S1 50 

560 -PHASE LOCK LOOP .... S2 00 

561 - PHASE LOCK LOOP .... S2.00 

565 - PHASE LOCK LOOP . . . . • S1 25 

566 FUNCTION GEN SI 65 

567 -TONE DECODER ...... si 50 

LM 1310N FMSTEREO DEMOD. . S2 75 

8038 IC VOLTAGE CONT. OSC. . S3 90 

LM 370 - AGC SQUELCH AMP. , $115 

555- 2^s -2 HR. TIMER § 45 

553 OUAD TIMER S2 50 

FCD 810 OPTO-ISOLATOR .... S 80 

1458 DUAL OP AMP S 60 

LM 380 2W AUDIO AMP $ .95 

LM 377 - 2W Stereo Audio Amp. . S2.50 

LM 381 - STEREO PREAMP. .,. S1.50 

LM 382 - DUAL AUDIO PREAMP S1.50 

LM 311 - HI PER. COMPARATOR S .90 

LM 319 - Dual Hi Speed Comp. .. S1.25 

LM 339 - QUAD COMPARATOR SI .50 



, PRV 1A 


10A 


25A 


1.5A 


6A 35A I 


1 100 .40 


.70 


1.30 


.40 


.50 1.20 


! 200 .70 


1.10 


1.75 


.60 


.70 1.60 


I 400 1.10 


1.60 


2.60 


1.00 


1.20 2.20 



Terms: FOB Cambridge, Mass. 
Send Check or Money Order. 
Include Pos 
Order $5.00, COD'S $20.00 



SOLID STATE SALES 

P.O. BOX 74B 

SOMERVILLE, MASS. 02143 TEL. (617) 5474005 



WESHIP OVER 95% 

OF OUR ORDERS THE 

DAY WE RECEIVE THEM 



• Accuracy: ±0.05% of Reading ±1 Count 

• Two Voltage Ranges: 1.999 V and 199.9 mV 

• Up to 25 Conversions/s 

• 2 in > 1000 M ohm 

• Auto-Polarity and Auto-Zero 

• Single Positive Voltage Reference 

• Standard B Series CMOS Outputs-Drives One Low Power 

Schottky Load 

• UsesOn-Chip System Clock, or External Clock 

• Low Power Consumption: 8.0 mW typical (§> ±5.0 V 
■ Wide Supply Range: e.g.. ±4.5 V to ±8.0 V 

MC14433 SINGLE CHIP 3*DIGITA/D 

Single chip combines linear and CMOS digital to bring you 

the simplest yet DVM approach „ Requiring only 4 external 

passive ports, this subsystem gives you: Auto polarity, auto 

zero, single voltage reference, 8 mW operation, overronge, 

underronge signals, 25 conversions per second and .05% ± 

1 count accuracy! 100 uV resolution. 24 Pin DIP. 

MCI 4433P with specs Si 9.55 



MC14412 UNIVERSAL MODEM CHIP 
MC14412 contains a complete FSK modulator and de-mod- 
ulator compatible with foreign and USA communications. 
(0-600 BPS) 
FEATURES: 

.On chip crystal oscillator 
.Echo suppressor disable tone generator 
.Originate and answer modes 

.Simplex, half-duplex, and full duplex operation 
.On chip sine wave 
.Modem self test mode 
.Selectable data rates: 0-200 
0-300 
0-600 
.Single supply 
VDD=4.75 to 15VDC - FL suffix 
VDD=4„75 ta 6 VDC - VL suffix 
TYPICAL APPLICATIONS: 

.Stand alone - low speed modems 
.Built - in low speed modems 
.Remote terminals, accoustic couplers 

MC14412FL. . . , S28.99 

MC14412VL S21 .74 

6 pages of data .60 

Crystal for the above $4.95 

MCI 4411 BIT RATE GENERATOR. 
Single chip for generating selectable frequencies for equip- 
ment in data communications such as TTY, printers, CRT s 
or microprocessors. Generates 14 different standard bit 
rates which ore multiplied under external control to IX, 
8X, 16X or 64X initial value. Operates from single +5 

volt supply. MC1441 1 , , SI 1 .98 

4 pages of data « 40 

)| Crystal For the above S4-.95 

REMOTE CONTROL TRANSMITTER. MC14422P is a 22 
channel ultra-sonic remote control transmitter I.C. CMOS 
uses little power and only a few external passive compon- 
ents. Applications include TV receivers, security controls, 
toys, industrial controls and locks. 16 pin DIP plastic pkg. 
MC14422P with specs SI 1 . 10 





MC6525 REMOTE CONTROL RECEIVER 

The MC6525 is o 22-chonnel remote control receiver circuit 
designed for use in television receivers, industrial remote 
controls, remote security controls, radio receivers, electron- 
ic games and similar applications. The circuit is intended for 
use with ths MCI 4422 remote control transmitter. Comes in 
28 pin DIP plastic package. 
MC6525P with 6 pages of specs SI 8.38 



3 DECADE (BCD) COUNTER CHIP 
MC14553BCP consists of 3 negative edge triggered 
synchronous counters, 3 quod latches and self scan 
multiplexed , TTL compotiple outputs. 

MC14553BCP $8.72 

Spec sheets $.60 



.LM1889 TV VIDEO MODULATOR 

The LM1889 is designed to interface audio, color difference, 
and luminance signals to the antenna terminals of a TV re- 
ceiver. It consists of a sound subcarrier oscillator, chrbmo 
subcorrier oscillator, quadrature chromo modulators, and R.F 
oscillators and modulators for two low-VHF channels. 
The LM1889 allows video information from VTR's, games, 
test equipment, or similar sources to be displayed on block 
and white or color TV receivers. 
LM1889 with 16 pages of data $9.95, data only, Si .00 



aaprjBon 



Soys 



IF YOUR PROJECT TIME AND MONEY ARE BEING 
BLOWN AWAY BY DELAYS AND HIGH PRICES — 
****** MARCH ON DOWN TO TRI-TEKJ ******** 



OKMACHINE 

AND 

TOOL CORPORATION 




HOBBY-WRAP TOOL 



HOBBY-WRAP TOOL 

Battery operated with built-in 30 go bit and sleev 
Uses standard C batteries (not included). Light we 1 
only 11 oz. Wraps standard DIP sockets. Has built 
device to prevent overwropping . Pistol grip, positive 
indexing. Quality construction assures exceptional 

performance. BW-630 $34,95 

FREE, a 50' roll of wire wrap wire with each tool!!! 



TL430CLP PROGRAMMABLE ZENER 

Brand new device type allows you to make your own zener 
by external programming. Turn those cheap fixed voltage 
regulators into rock solid adjustable by adding this little 
feller, 1 resistor and a pot. Use for min/max indicators, 
settoble crowbar, shunt regulator, clamp. 
Be the first one on your block to use this new and interest, 
ing part. 

TL430CLP $1 .00 

Specs and applications 30c 



93S41 SUPER FAST 4-BIT ALU 

All 16 possible logic operations on two variables plus arith- 
metic. Shottky diodes on input for high speed. Same as 
74S181. 
93S41 $1 .98, 4/S6.00 




DATA BOOKS BY NATIONAL SEMICONDUCTOR 

DIGITAL. Covers TTL, DTL, Tri-State, etc $3.95 

LINEAR . Covers amplifiers, pre-amps, op-omps. . . $4.25 
LINEAR APPLICATIONS VOLUME I. Dozens of 
application notes and technical briefs covering the 
use of op-amps, regulators, phase locked loops and 

audio amps S3. 25 

LINEAR APPLICATIONS VOLUME II . Tokes up where 
Volume I left you — All the latest linear devices. 
Along with Vol I you have a great source of app- • 
lication data on the most widely used devices as well 

as new types just oppeoring $3.25 

CMOS Gates, Flip Flops,' registers, etc $3.00 

VOLTAGE REGULATORS. A friust for anyone making 
a power supply. Complete theqry including transform- 
ers, filters, heat sinks, regiilotors etc S3. 00 

MEMORY. Info on MOS and Bipolar "memories, RAMS 

ROMS, PROMS and decoder/encoders $3.95 

INTERFACE. Covers peripheral drivers, level trans- 
lators, line driver/receivers, memory and clock drivers, 

sense amps, display driver and opto-couplers S3. 95 

SPECIAL FUNCTIONS DATA BOOK. Contains de- 
tailed information for specifying and applying special 
amplifiers, buffers, clock drivers, analog switches and 

D/A-A/D converter products $3.25 

AUDIO HANDBOOK Contains detailed discussions, 
including complete design particulars, covering many 
areas of audio with real world design examples... S3. 25 

SPECIAL 

DATA BOOKSHELF. Buy oil ten of the Notional Data 

books at one time and save 55.10!!! $30.00 

(All books shipped ppd in US only. Foreign orders 
please odd shipping for 1.5 lbs per book) 



HOBBY-WRAP-30 Handy little tool to strip, 
wrap and unwrap 30 gouge wire $5.95 




LDPLITE™ 

COMBINATION LENS AND 

MOUNTING DEVICE FOR 

T l 3 /4 LED 

REQUIRES 

NO TOOLS 



SNAP CLIPLITE 




°0¥ 



msiKT no 



AVAILABLE IN TRANSPARENT RED- CREEN - AMBER -CLEAR & YELLOW 

SZLIPLITE 

Combination lens and mounting device for T 1-3/4 LED, 
The CLIPLITE combines the benefits of the present LED 
display panel mounting methods and eliminates their def- 
iciencies. Requires no special tools and installs in 6 seconds 
in .250" hole. Simple two-step installation. Just snap 
CLIPLITE, insert LED. Available in transparent red, green, 
amber, clear and yellow. Specify colors, any mix. 
5/S1.00, 10/S1.90, 20/S3.50, 50/S7.50, 100/S13.50 



78H12 HIGH CURRENT REGULATOR 

Now, a 12V, 5A regulator in o single TO-3 package!! 

Internal short circuit limit and thermal overload protection. 

Some ease of application as the popular 309K 

78H12 with specs $14.25 



SN75450 DUAL PERIPHERAL DRIVER 

Two identical NAND gates and two 30V, 300mA unconnec- 
ted NPN transistors in a 14 pin DIP package. Use for 

lamp and LED drivers, cable drivers, relays etc. 

SN75450N 45.;, 10/S3.90 

5V, 3Amp O. E.M. Power Supply. Adjustable current 
limit. Su pe r good specs $29.95 

FIXED VOLTAGE 1 AMP REGULATORS 

+5V in TO-3 98c; 

+5V in TO-220 Power Tab 95$ 

+12V in TO-3 SI. 19 

+12 V i n TO-220 Power Tab SI .09 

+15 in TO-3 SI. 19 

+ 15V in TO-220 Power Tab Si .09 




tRi-tek, inc. 

6522 noRth 43r0 avenue, 

Qlen&Ale, arizoiia 853oi 

phone 602 - 931-6949 



We pay surface shipping on all orders over $10 US, $15 foreign in US funds. 
Please add extra for first class or air moil. Excess will be refunded. Orders 
under $10, odd $1 handling. Please odd 50$ insurance. Moster charge and 
Bonk America cords welcome, (S20 minimum). Telephone orders may be placed 
10AM to 5:30PM daily, Mon thru Fri . Call 602-931-4528. Check reader 
service cord or send stamp for our latest flyers pocked with new and surplus 
electronic components. 






Reader Service 



•Reader service inquiries not solicited. 
Correspond directly with company. 



To get further information on the products advertised in BYTE, fill out the reader 
service card with your name and address. Then circle the appropriate numbers for the 
advertisers you select from this list. Add a 9 cent stamp to the card, then drop it in the 
mail. Not only do you gain information, but our advertisers are encouraged to use the 
marketplace provided by BYTE. This helps us bring you a bigger BYTE. 



Reader 

Service 

Number 

75 Advanced Microcomputer Prods 147 

173 Anderson Jacobson 143 

4 BITSInc86, 87 

153 Bits, Bytes and Pieces 141 

* BYTE's Binders 136 
200 California Industrial 148 

126 Cheap Inc 141 

127 Comptek135 

140 Computalker 141 

* Computer Faire 68, 69 
83 Computer Mart NY LI 141 

156 Computer Place 143 

141 Computer Room 89 
208 Computer Shack 83 
206 Computer System Design 139 
203 Computer Systems 66 
197 Computer Systems Center SL 141 
199 Computer Transceivers 137 
138 Computer Warehouse 149 
202 CRC Engineering 133 

87 Creative Computing 134 

41 Cromemco 1, 2 

178 Cybercom 11 

185 DAJEN Electronics 66 

78 Digital Group 17 

210 MWDunton66 
170 ECDCIII 

211 Economy Terminal 129 
47 Electronic Control Tech 139 

157 Electronic Warehouse 150 





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64 




102 


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198 




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194 




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213 




204 


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24 




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167 




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201 




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McGraw-Hill 27 


27 




18 


Meshna 155 


169 


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Micronics 141 


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174 


Microtex 139 


99 




119 


Midwestern Sci Inst 138 


164 


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Mikos 156 


96 




112 


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205 




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MITSCIV / 84 r 85 


121 




62 


Morrow 145 


82 




71 


mpi 121 


136 




132 


M&R Enterprises 143 


192 




171 


Mullen 131 


32 




# 


National Computer Conf 132 


212 




22 


National Multiplex 37 


193 




155 


North Star Computers 93 


137 


) 


40 


Ohio Scientific Instr 33 


154 



Page 
Number 

Oliver Audio Engineering 139 

Omni 103 

Parasitic Engineering 129, 133 

PerCom Data 96 

Peripheral Vision 81 

Polymorphic Systems 25 

Prime Radix 127 

Processor Technology 5, 6, 7, 8, 9, 63 

Quay 98, 99 

Riverside Electronics 105 

Scelbi 29 

Scientific Research 65 

SD Sales 157 

Smoke Signal Broadcasting 135 

Solid State Sales 158 

Southwest Tech CM 

STM 145 

Sunny Computer Stores 143 

Synchro-Sound Enterprises 79 

Szerlip Enterprises 121 

Tarbell Electronics 125 

Technical Design Labs 49 

Technical Systems Consultants 137 

Tec Mar 119 

TriTek 159 

University of Texas 143 

US Robotics 143 

Vector Graphic 12, 13, 35 

Worldwide Electronics 91 



BOMB- ' 

BYTE's Ongoing Monitor Box 



On BOMB Card, 
Article No. 



ARTICLE 



1 Grappel: Give Your Micro Some Muscles 

2 Kay: PR-40 Alphanumeric Printer Review 

3 Freeman: Cassette Transports for "Roll Your Own" 

4 Bremeir-Rampil: Digital Cassette Subsystem, Part 2 

5 Frenzel: What's Involved in Kit Building? 

6 Burhans: Simplified Omega Receiver Details 

7 Buschbach: Inexpensive Joystick Interfaces 

8 Price: Flights of Fancy with the Enterprise 

9 Ciarcia: Try This Computer on for Size 

10 Hogenson: Multiplex Your Digital LED Displays 



PAGE 

9 

18 

26 

38 

50 

70 

88 

106 

114 

122 



BOMB's Best Liked for December: 
Cybernetic Crayon, Weather Predicting 

Thomas A Dwyer and Leon Sweer of the 
Soloworks Lab at the University of Pitts- 
burgh will share the $100 bonus for the 
readers' most favored article in December 
1976 BYTE, "The Cybernetic Crayon." 
Michael R Firth takes a $50 prize for "Do 
It Yourself Weather Predictions," the run- 
nerup. December's contest was the last of 
the "old fashioned" BOMBs, with voting 
done by photocopying or tearing out part of 
the last page. Now you can vote for yout 
favorite articles by using the BOMB card 
inside this BYTE; just get it in before April 
1 1 977, the deadline for March entries." 



160 






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E|JXK: READER SERVICE 
Et I E Publications Inc 
70 Main St 
Peterborough NH 03458 




U SUBSCRIPTIONS 
Publications Inc 

70 Main St 
Peterborough NH 03458 




EYTEs (jdftinf Mcmttr< ttx 



EV I WL Publications Inc 
70 Main St 
Peterborough NH 03458 



Tht (ED *»«-*' ««crot»«< dliplav prtctntr tiipiwi irohie* im 

Cftie4siie EfiOii — hi or rtrmt I « 12. nrtvwi- 

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ftrtphiet. nothing etn touch tt. 



Key Into 
Maxi-Power <£> Micro-Price 



Micromind is an incredibly flexible, 
complete and expandable, hardware/ 
software, general purpose computer 
system. You won't outgrow it. 

Hardware includes an 80 key, software- 
definable keyboard, I/O interface board, 
6500A-series microprocessor (powerful 
enough for advanced computing), a high- 
detail graphics and character display 
processor, power supply, rf modulator, 
and connections for up to 4 tape recorders 
'• is TV or monitor. An interconnect bus 




permits 15 additional microprocessors, 
parallel processing and vastly increased 
computing power. 

System software— including ECD's own 
notsoBASIC high level language, on 
advanced error-correcting tape cassettes 
—provides a word processing editor, a 



Name. 




powerful assembler, a debugger, a file 
system, graphic routines, and peripheral 
handlers. We also include dynamic graphic 
games: Animated Spacewar and Life. 
ECD's standard Micromind /u,M-65 
supplies 8K bytes of memory. Additional 



32K byte expansion boards and a mapping 
option give Micromind expandable access 
to 64 Megabytes . Utilizing software- 
controlled I/O channels, Micromind's 
advanced encoding techniques load data 
from ordinary tape recorders at 3200 
bits per second. 

Micromind comes to you ready-to-use, 
factory assembled and fully tested. Among 
microcomputers, it has the largest memory 
capacity and the fastest storage. You're 
looking at the work of the finest display 
processor on the market. You won't find a 
microcomputer with a more powerful CPU. 
You won't find a computer with a 
more flexible keyboard. You won't 
find anything to 

touch it at 
$987.54. 





So, quit the kluge scene and key into 
Micromind. You'll be a main frame per- 
former, with all the comforts of home. 
We're not fooling . . . this ]s the cat's /it! 

ECD CORP. 
1 96 Broadway, Cambridge, Mass. 02139 
(617) 661-4400 



€CD 



Address . 



City/State . 



Zip. 



□ Fantastic! Check enclosed: $987.54. shipping paid by ecd 

□ BankAmeriCard □ Master Charge Mass. Resident add 5% Sales Tax 



# 



Expiration Date . 



Signature 

D Send me your brochure. 

Actual unretouched photographs. 



Now you can buy an 

Altair*8800b or an Altair 

680b computer right off 

the shelf. Altair plug-in 

boards, peripherals, 

software and manuals 

are also available. 

Check the list below 

for the MITS 

dealer in your area. 




off the shelf. 



ALTAIR COMPUTER CENTER 
8105 SW Nimbus Ave. 
BEAVERTON, OR 97005 

COMPUTER KITS (S.F. area) 
1044 University Ave. .- ' 
BERKELEY, CA 94710 

(4151-845-5300 

THE COMPUTER STORE 
(Arrowhead Computer Co.) 
820 Broadway 
SANTA MONICA, CA 90401 

(2131-451-0713 

GATEWAY ELECTRONICS, INC. 
OF COLORADO 
2839 W. 44th Ave. 
DENVER, CO 80211 
(3031-458-5444 

COMPUTER SHACK 
3120 San Mateo N.E. 
ALBUQUERQUE, NM 87110 

(5051-883-8282; 883-8283 

ALTAIR COMPUTER CENTER 
4941 East 29th St. 
TUCSON, AZ 85711 
(6021-748-7363 



ALTAIR COMPUTER CENTER 
611 N. 27th St. Suite 9 
LINCOLN, NB 68503 
(402) 474-28.00 

COMPUTER PRODUCTS UNLIMITED 

2412 Broadway 

LITTLE ROCK, AR 72206 

(50D-371-Q449 

ALTAIR COMPUTER CENTER 

110 The Annex 

5345 East Forty First St. 

TULSA, OK 74135 

(9181-664-4564 

ALTAIR COMPUTER CENTER 
5750 Bintliff Drive 
HOUSTON. TX 77036 
••{7131-780-8981 

CpMPUTERS-TO-GO 
4503 West Broad St. 
RICHMOND, VA 23230 

(8041-335-5773 

MICROSYSTEMS (Washington. D.C.) 
- 6605A Backlick Rd. 
SPRINGFIELD, VA 22150 

(7031-569-1110 

THE COMPUTER STORE 

Suite 5 

Municipal Parking Building 

CHARLESTON, W. VA. 25301 

(3041-345-1360 



THECOMPUTER ROOM 
3938 Beau D'Rue Drive 
EAGAN, MN 55122 
(612)-452-2567 

THE COMPUTER STORE 

OF ANN ARBOR 

310 East Washington Street 

ANN ARBOR, Ml 48104 

(3131-995-7616 

THE COMPUTER STORE, INC. 

(Hartford area) 

63 South Main Street 

WINDSOR LOCKS. CT 06096 

(2031-627-0188 

CHICAGO COMPUTER STORE 

517 Talcott Rd. 

PARK RIDGE, iL 60066 

(312)-823-2388 

GATEWAY ELECTRONICS, INC. 
8123-25 Page Blvd. 
ST. LOUIS, MO 63130 
(314)-427-6116 

BYTE'TRONICS 
Suite 103 
1600 Hayes St. 
NASHVILLE, TN 37203 

(6151-329-1979 



THE COMPUTER STORE, INC. 
120 Cambridge St. 
BURLINGTON, MA 01803 
(617)-272-8770 

ALTAIR COMPUTER CENTER 
269 Osborne Road 
ALBANY, NY 12211 

(518)-458-6140 

THE COMPUTER STORE 
OF NEW YORK 
55 West 39th St. 
NEW YORK, NY 50018 

(2121-221-1404 

THE COMPUTER SYSTEMCENTER 
3330 Piedmont Road 
ATLANTA, GA 30305 
(4041-231-1691 

MARSH DATA SYSTEMS 
5405 B Southern Comfort Blvd. 
TAMPA, FL 3 3 614 
(813)-886-9890 



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