1976_02_07 1976 02 07

User Manual: 1976_02_07

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Tab!e of Contents
Bits and Pieces
Monitor in Lumber Production
CMPCTER-LOADER
HAM on the Side
Sma!! Computer Networking
Q&A Hardware C!itches
Fieid Testing the Aitair 8800

2
4
6
9
10
14
16

iU+=I%Xi—;/-;;/.;-;.;;

LETTER
TO THE EOtTOR
Dear Ed.,
While programming my Altair
computer, I detected a potential
problem with the 8800 SIO-B (ACR)
I/O card which may be of interest
to other users. Although there
is a solution, it's not entirely
satisfactory. I hope someone
else can supply a better one.
The problem is that an input
program written at one location will
work while at another it won't.
The program and the address at which
the program won't work is listed
as follows:

001 IN
002
Stat chan
003 RRC
004 JC
005
L
006
H
007 IN
010
Data chan
011 ETC

333
002

017
332
001

any page
333
003

The problem occurs if the program
is written in a location such
that the low order address of the
instruction (RRC) following the
input instruction (2nd byte) is
equivalent to the data channel
address which is 003 in this case.
The result is that if a string of
characters is being input, about 1
in 20 will be lost.

During machine cycle 1 (Ml) of
the input instruction (see Figure 1),
the first byte (333) is read into
the processor and during M2 the address of the device (002-status
channel) is read in. During M3 the
processor outputs the device number
(as an address) from which data is
also to be read. The processor
reads in the data during T3 of M3.
During each of the machine
cycles of any instruction, the processor outputs a status word which
is latched into the status register
(on the CPU card) by the coincidence
of 01 and sync. The status word is
used to control memory and I/O
cards. In this case the status

Bits a n d Pieces
BY:

On
The
C over

SONDRA KOPPENHEFFER

FATAL ACCIDENT DAMPENS THE CHRISTMAS
SPIRIT

UPDATE SERVICE TAKES A SEAT IN
HISTORY

Sending Christmas packages
through the mail is a part of the
holiday spirit. However, packages
have been known to experience quite
a lot of trauma before reaching
their intended destination. Let me
contrive an example to convey the
message of this article.

The advertisement for Computer Notes
Review, Vol. 1, has generated many
inquiries concerning our update
service. However, this service was
discontinued six months ago. We feel
that any benefits you would have
received through the Update Service,
are now directly available in
Computer Notes.

Your disk, never having much
of a Christmas spirit, has decided
to take a vacation. No amount of
intuition or technical ability will
convince that marvel of technology
to work. Giving up on the disk,
for more enjoyable holiday activities,
you finally decide to give MITS a
try at repairing the disk.
. . . About a week later, you
receive a phone call from MITS,
explaining that your disk had been
involved in a fatal accident. Upon
arrival at MITS, the disk had been
severely damaged, and the $200.00
for which you had insured it, wasn't
nearly enough to cover the doctor's
bills. Your bereavement is turned
into shock when you are told that
you will have to pay a $350.00 bill
for repair of the disk.
The gentleman in this story
had to learn about our postal system
the hard way. But this type of
misfortune should be a lesson to all
Altair owners who send their units
back to MITS for repair. Always
insure your system for at least the
amount that you originally paid for
it. Even if the case is the only
part of your system damaged in transit, you will still be billed $170.00
for repairing the case.
So remember to send us your
unit by registered mail and make
sure it's insured for the full
amount.
Page Two

This picture of Ron Roberts,
president of the Altair Software
Distribution Company, is just one
example of digital art produced
on an Altair 8800b computer.
This system was developed
by The Computer Systemcenter
in Atlanta and uses a Panasonic
video camera, a Centronics printer
and a commercially available
digitizer, in addition to an
8800b with special interfaces and
custom'software.
The system works by
assessing the relative amount of
gray in a TV picture, setting a
character on the printer that
approximately corresponds to that
perceived amount of gray and
finally, printing the picture.

CUSTOMERS SUBMIT MISSING PAPER
REPORT - MASSIVE SEARCH BEGUN *
AT MITS
This paragraph is dedicated to
all those customers who have recently
purchased an Altair computer through
one of our dealers. We've received
many calls and letters asking why
new customers have not started
receiving Computer Notes. We depend
upon our dealers to submit the names
of all those persons who purchase an
Altair through their store. This
procedure generally takes three
weeks to one month. Once in a while
a dealer inadvertently misses a
name and we are therefore unable
to place that customer's name on
our mailing list. If you find yourself in the situation which I just
described, please contact the dealer
from whom you purchased your Altair.
Following up on this procedure will
help limit any duplication in your
subscription.
COMPLETE RECORD OF PURCHASES NEEDED
If you have ordered systems
through both MITS and one of our
dealers, you might find it to your
best interest to send us copies of
all of your dealer purchases so
that we might update your file. If
we have complete records for all
Altair products which you have
purchased, you can depend on much
more efficient and rapid service.
Continued on Page Seven

C O M P L E T E R
y

" [ i O T E S
Editor
Andrea Lewis
Asst. Editor Linda Biocki
Production Tom Antreasian
A) M c C a h o n
Steve Wedeen
Grace B r o w n
Contributors Tommy Staten
GeneDiai
Charies Oisen
Dougtas L. J o n e s
Mike Hunter
Bob Matthews
Sondra Koppenheffer
Jim Wiggins
Rich Haber
Bruce Fowter

CN/December 1 9 7 6

VMACC-H
SLATED FOR MAY

Book Review

By Charles Olsen
Practical Microcomputer Programming
The Intel 8080
The second annual World Altair
Computer Convention(WACC-II),
scheduled for May 18-21 at the
Albuquerque Convention Center,
promises to be even more
spectacular than last year's,
with the largest collection of
Altair equipment, dealers and
computer experts anywhere in the
country.
Attendance is estimated at
more than 1,000 computer
enthusiasts, which is well over
the unexpected 750 people who
gathered at last year's WACC.
The four-day convention will
be geared to both the hobbyist and
small businesses but will also
include displays of many other
special applications for large
businesses, industry, education
and the home.
All of our Altair dealers will
be at the convention to display
various systems and answer any questions.
A banquet will be held on May
20, and the last day of the convention will be reserved for various
special events, such as awarding
prizes and conducting tours of the
Albuquerque-Santa Fe areas.
Lodging will be available
at the Albuquerque Inn, which is
connected by an underground
walk-way to the Convention
Center next door. Only those
people who confirm their
reservations early will get
their choice of rooms at the
Albuquerque Inn. Additional
accommodations will be
available at the local
Sheraton and Hilton hotels,
only a 10-minute drive
from downtown Albuquerque.
Details concerning the
WACC-II schedule, seminars,
dealer contacts, prizes and
tickets for the banquet will
appear in next month's issue
of Computer Notes as well as
other computer magazines.
If you have any further
questions about WACC-11, please
feel free to contact me.

Charles Olsen
Director of PR
MITS, Inc.

CN/December 1 9 7 6

By:

Mike Hunter

Although most microcomputer
users usually prefer to use a
high level language, such as BASIC,
when writing programs, they are
often either compelled by necessity or motivated by interest to
use machine code or assembler
instead. Learning how to manipulate
the ones and zeroes as well as the
various mnemonics can be confusing
for anyone. But it's particularly
devastating to the programmer who
has only one or two kilobytes of
memory and thus has no other choice
but to use machine code.
The literature available from
the chip manufacturers sometimes
provides only brief explanations of
machine code functions. For the
novice microcomputer user, such
descriptions are often as cryptic
as the mnemonics. One excellent
solution to this problem is Weller,
Schatzel and Nice's brand new book,
Practical Microcomputer Programming
The Intel 8080.
The book provides the novice
with over 300 pages of all the
information necessary to begin
programming a microcomputer.
Although the book is aimed at beginners, it's still a very helpful,
detailed source of reference material
for programming experts.
The 18 chapters of the book
cover a wide variety of topics, including binary addition, how to
use the stack pointer and how to
interface the 8080 to complex
peripherals. Each chapter begins
with a discussion of a basic concept
followed by instructions on how to
implement the concept with the 8080
machine code.
The book is based on a conTM
figuration consisting of a Teletype
and an Altair 8800, which was
assembled by one of the authors.
The authors wrote their own unique
assembly program to be used as the
main example program throughout
the book.
Many instructive texts are
often boring as well as difficult
to understand. However, Practical
Microcomputer Programming is not
only interesting but is written in
a style that even beginners can
follow. The authors help alleviate the drudgery and confusion
of working through examples b y
using such names as Tom, Dick and
Harry as variables rather than
the traditional X and Y .

The final chapters of the
book discuss such questions as,
"How do I interface my 8080 microcomputer to an analog device, or
terminal, and how can it be used in
a real time mode?"
The last chapter deals
appropriately enough with the final
step in the programming process—debugging. This chapter describes
many procedures for discovering the
source of an error.
In general I'd recommend this
book as a valuable source of
programming information for any
8080 microcomputer user.
Practical Microcomputer Programming—The Intel 8080 is
available for $21.95 from:
Northern Technical Books
Box 62
Evanston, 111. 60204

N e w
F

o

C ! u b
r

m

e

d

State University of New York at
Stony Brook recently formed the Home
Brew Computer Club to promote informal discussions of a variety of both
hardware and software topics. Most
members have their own systems (8080
and 6800) to discuss and demonstrate.
The club also has access to a number
of simulators and cross-assemblers
on the university computer. For
further information, contact:
Ludwig Broun
Professor of Engineering
College of Engineering and
Applied Sciences
State University of New York
at Stony Brook
Stony Brook, NY 11794

The Altair User Group Software
Library is in the process of being
transferred to the same facility
that houses the new Altair Software
Distribution Company. Because we
are in the middle of this transition
and because there were only a few
entries for December, no contest
winners were chosen this month. All
entries received in December will
be included in the January contest.
Check the January issue of
CN for further new developments in
the Altair Users Group Software
Library.
Page Thirteen

Case Study:

Monitoring Lumber Production
with an Altair Computer
By Tommy Staten
Ms.. &tate.M.
m^ZZ m a n a g g A
H.C. Hodges LumbgA Compact/
Panama C^tt/, F f o ^ ^ a .

Since the H. C. Hodges Lumber
Company first opened, we've had
difficulty keeping track of our
production. The lumber was being
tallied daily as it was stacked,
but at the end of each month, there
was a considerable discrepancy between what was counted and what was
inventoried. Obviously, this caused
quite a few problems. So I devised
a method of using an Altair computer
to monitor production.
I chose the Altair 8800 microcomputer because I am convinced that
no other manufacturer matches the
MITS Altair system in either hardware or software support. Price was
also a factor. Although the Altair
is not the cheapest computer on the
market, it has proven it was certainly
worth the cost by being a very reliable and efficient system for our
lumber company.
The following description is
only one example of how an Altair
system can be used in an industrial
application. The possible uses of
such a microcomputer system are
almost limitless, not only within
the lumber industry but in any
operation where production control
and cost effective monitoring
systems are required.
In the past three years more
and more manufacturers have begun
to incorporate solid state
electronic circuitry in their
system controls rather than using
the usual magnetic relays,
mechanical switches, limit swiches,
etc. These methods were fine for
the actual operation of a machine,
but they proved to be very clumsy
for automatic control of equipment.
The advent of solid state
electronics in system controls
has resulted in increased
production that's less expensive
and more efficient. With
automatic controls, "down time"
or lost production is also minimal.
The lumber industry is a prime
example of how solid state
electronics in system controls have
been effectively used to accurately
monitor daily production while
saving both time and labor costs.
Four years ago the average lumber
mill used 15 to 20 men to sort and
stack rough cut lumber as it came
out of the mill. The usual
procedure utilized a 150-foot
lumber conveyor chain that moved
the lumber from the cutting saw
area. As the lumber came out,
men stationed on both sides of
the conveyor would pull, sort and
P a g e Four

stack the lumber according to size.
Today, that long conveyor still
exists, but instead of 15 men,
only one--the control operator--is
needed to get the job done. This
change was made possible by using
a new dropsorter built by Harvey
Engineering, Little Rock, Arkansas.
The dropsorter is a low voltage,
solid state binary logic control
system that uses primarily CMOS ICs
and some TTL. Although the limit
switches were not entirely eliminated, their use was limited strictly
to generating timing and measurement
signals. The following description
explains how the system works.
Dropsorter:
Sequence of Operation
The dropsorter control logic
system is composed primarily of
five printed circuit boards interconnected with 26 conductor ribbon
cables. Control system input signals
of 24 VDC are supplied to the I/O
board from limit switch contact
closures and/or operator control
push buttons.
When a piece of lumber
passes through the measuring
section of the sorter infeed,
certain limit switches are
actuated, and width, length
and thickness signals are coupled
from the I/O board to the measuring
board where they are connected
to 12 VDC binary logic. The
signals are then coupled to the
display board, which displays the
actual board dimensions. A proper
dimensional display indicates that
the external switches,'I/O board
and measuring board are functioning
properly.
At the same time the input
signal is displayed, the binary
coded signal is also fed to the
program coding board. The function
of the coding board is to assign a
two-bit binary bay address to each
major lumber dimension(represented
by the binary coded signal).
Any lumber dimension which does not
have a programmed lumber bay address
is automatically dropped in a
designated drop-out bay.
The two-bit binary bay address
is coupled from the program board to
the memory or shift board, where
the binary bay address can be seen
from the time a piece of lumber is
measured until the reset limit
switch resets the system for the
next measurement. The two-bit

binary address also enters a multichannel shift register, which shifts
one position for every revolution
of the dropsorter head shaft. The
d u m b e r of shifts required for a
board to travel to a specific bay
must be predetermined, and the
memory or shift board should be preprogrammed for the proper number of
shifts before sending an output
signal to a designated bay.
Custom Interface Required:
The display board uses TTL
logic exclusively and supplies the
necessary signals for our interface.
The interface was designed for us by
Warren Stardup, who is a partnertechnician with Microcomputer Systems,
Inc. of Tampa, Florida.
The interface converts the TTL
to serial, using a UART (Universal
Asynchronous Receiver Transmitter).
Data is then transmitted from the
mill site to the office computer via
a 20 mA current loop. Each board
size is represented by a standard
ASCII Character. The proper ASCII
code is signaled to the UART through
a diode matrix on the interface
board.
System Configuration:
The system includes an Altair
8800 computer with an upgraded power
supply and memory that consists of
two Dutronics 8K Static RAM boards
and one MITS 4K Dynamic Memory board
for a total of 20K. However, only
about 10K bytes of this are used for
both the BASIC interpreter and the
lumber program. Both programs are
loaded into the Altair computer
through a MITS ACR board.
I hope to have our MITS PROM
board with the BASIC bootstrap
loader up and running soon, because
so far, I'm the only person who can
load the computer. On several occasions I've been rousted from bed to
go down to the mill during the night
shift, because a thunder storm has
caused a momentary loss of power.
Somehow, these power failures always
seem to occur during my "off" shift,
usually when I'm at home in bed.
The lumber data comes from the
interface to one port of a MITS 2SI0
board. This port is wired for a
20 mA current loop. The other port
on the 2SI0 board is wired RS232
and connects an ADM-3 Lear Seigler
Continued
CN/December 1 9 7 6

8080

Monitoring Lumber Production
With an Altair Computer
Continued

programming
problems?

CRT to the processor. All data is
displayed and constantly updated on
the CRT. The information shown on
the CRT is copied down by hand at
the end of each shift. We also have
a spare SWTP video terminal and hope
to acquire some sort of hard copy
printer in the very near future.
Software:
The software was written by
Bill Turner, a software genius from
Microcomputer Systems, Inc. of Tampa.
Bill is also one of the well-known
authors of SWTP's BASIC.

!F you need to know how to:

Our program is written in 8K
BASIC. Data is displayed in a two
dimension matrix (7,6). The display
is constantly updated as each board
is measured. Boards actually come
through the sorter at a rate of one
every two seconds, so most of the
processor's time is spent simply
waiting for an input. To make use
of this wasted time, I plan to use
another interface which will scan
the logs as they are about to be cut
and compute the measurement with
what comes out of the sorter, to
give the actual recovery of all logs
that are processed.

* service interrupts
* domutti-precision
arithmetic
+ convert n u m b e r bases
* h a n d i e arrays a n d tabies
* controicompiex
peripherais
* u s e the stack pointer

The program also has the ability
to record all data accumulated on a
cassette tape, at a predetermined
board count, which is usually every
1,000 boards. In case of a momentary
loss of power, this will preserve
all of the data accumulated at that
particular time. The cassette obviously won't be needed once we get
the printer.
Since we began using the Altair
system, our inventory discrepancies
have been eliminated, much to our
bookkeepers' appreciation. But the
real merit of the system is that
now office personnel can simply
glance at the CRT to see exactly
what is being produced in the mill.
If we have orders for long stock,
but the trend on the display is
for short stock, we simply get on
the intercom and ask our workers to
cut the long pieces into shorter
ones. This proves invaluable
when dealing with truckloads of
orders which vary in size from
day to day.

CN/December 1 9 7 6

* d e b u g your programs

THEN

. . . Practica! Microcomputer Programming:
The !nte! 8080 is the book you've been waiting for. Written by
apptication programming peopie for apptication programmers,
this is not a book of theory, but a book of step by step
soiutions to rea! probtems. !n eighteen chapters and more
than 100 exampte programs it shows you exactty how to do
ait of the things tisted above and many, many more with 8080
assembty !anguage. A comp!ete programmer's guide to using
the 8080, it aiso contains the futt source text of a minicomputer cross assembier and a debug program for 8080
based systems. This couid be the best programming
information bargain you wii! ever see.

<
)

K
<

CN

Northern Technotogy Books
Box 62, Evanston, [itinois 60204

Ptease send my copy of Practica! Microcomputer Programming:
The tnte) 8 0 8 0 at $21.95.
ED check enctosed

H
H
!
H

Name

!

Company

H

Address

!

City

D money order enciosed

tMinois residents add $ 1 . 1 0 state saies tax. NcfC.O.D. piease.
Ptease type or print

State.

ZipPage Thirteen

CMPCTER-LOADER
Masters Paper-Tape Reader
BY:

DOUGLAS L. JONES

The Altair 680b PROM monitor is
truly 256 bytes of total cleverness.
It enables you to (L)oad, (M)emory
inspect and modify, increment to the
(N)ext address, (J)ump to a program
that is in memory or (P)roceed from
the presently interrupted point.
That's a lot of software power on a
little ROM chip.
If the I/O part of my computer
system, an old clunker model-33
T e l e t y p e ^ were up to snuff,
everything would be just fine. But
it isn't so. Couple the insatiable
ability of my clunker 33 to drop
bits on the paper-tape reader with
the checks and cross-checks of the
(L)oad loop in the PROM monitor, and
you've got instant frustration.
CMPCTER-LOADER was written in an
attempt to show that man is able
to master even a paper-tape reader.
The
supports
Motorola
consists

Altair 680b PROM monitor
what is know as the
paper-tape format. This
of three important points:
S0

(ignore) (ignore)

S1BBAAAADDDDDDDDCC
S9

(ignore) (ignore)

Where:
S0=Start of a header block
which for our purposes
can be ignored.
Sl=Start of a valid
data block.
BB=Block count of all
remaining data in this
block.
AAAA=Start address to load
DDDD=Hexadecimal data being
loaded.
CC=Checksum value.
S9=A11 data blocks finished
(return to exec . . or
whatever).
The data blocks are in ASCII and
are printable as local copy on the
T e l e t y p e ^ . Each is followed by
carriage returns and line-feeds.
Since they are not part of the data,
these characters will not be 'loaded'
but will only perform machine control—
a well thought out format in all respects.
The PROM monitor easily handles
this Motorola Format. The (L)oad
command will cause the monitor to
begin the load loop routine. Any
data that does not begin with 'SI'
is totally ignored. Once recogni-

tion of an 'SI' data block-mark
occurs, the monitor is locked into
a data-block format:
1.

2.

3.

Only hexadecimal characters
are allowed-up to and
including the checksum.
The checksum is actually
computed and must agree
mathematically with the
data being loaded.
An S9 data block will
terminate loading.

But herein lies part of the
problem. A jump out of the load loop
and back to the EXEC of the monitor
will occur not only on recognition of
an S9 data block, but also in the
middle of a valid data block, if it
recognizes a non-hex character, or
at the end of a data block if the
checksum computed is not correct.

Functionally:
10
20
30

RECEIVE BUM CHARACTER
JUMP OUT OF LOAD LOOP
AND BACK TO EXEC
SEND OUT PROMPT (CR)
(LF) (.)

40

RECEIVE A CHARACTER

50

IS IT (L), (J), (M), (N),
or (P) ??
HECK NO (LAUGH A LITTLE)
THEN JUMP TO 30

60

Relief is on its way. First, by
sending either a constant B1 or a D1
to the TeletypeTM port (address F000),
the paper-tape reader can be under
complete software control. That
should solve half of the problem--let
the computer control the paper-tape
reader.
Let's look at something else:
S11300A0BD...

Imagine trying to load a rather
lengthy paper tape such as the MITS
680 BASIC, with the PROM monitor.
The (L)oad command is typed and the
paper tape started. One of the first
data blocks loaded is address 00F3
with a constant FF. This will at
least kill the echo so that your
printer does not type out some 480
lines of 'Sldatadatadatadata...".
But the loading of the tape is
rather boring so you decide to run
up-stairs to make coffee, or to
watch some more of the movie...
and that's when it happens.

BD is to be loaded at address 00A0.
We want to deposit a binary 10111101
at that address. But the 'B' is
ASCII 01000010 and the 'D' is ASCII
01000100. Half of each character is
information saying that "this is an
ASCII character". So it takes a lot
of software shennanigans to strip off
the ASCII, left justify, inclusive OR
the data, etc., just to load BD at
one address. If the BD were in
binary on the paper tape to begin
with, it could be loaded at the
appropriate address in half the
number of paper-tape characters.

Inevitably, the paper-tape
reader will goof. It might read
one of the data characters as a non-hex
character and/or it will compute a
checksum incorrectly. The PROM monitor says to itself: "Ok. You blew
it. The heck with this incorrect
jazz, it's back to the EXEC for
me."

So it looks like we're going to
build a LOADER. It will accept pure
binary data, so it will cut the load
time considerably. It will recognize bummers and will stop the papertape reader. These were the starting criteria for the dual programs
CMPCTER-LOADER.

The program falls through the
load loop and returns to the EXEC at
entry line CRLF. The EXEC will
respond with a (CR) (LF) and then
a prompt character (.).
After the prompt character, the
only thing that is supposed to be typed
is (L), (M), (N), (J) or (P). But
t!?§ paper-tape reader has meanwhile
continued on its merry way. It
does not stop shoving non-command
characters into the PROM. The PROM
is out of the load loop and, therefore,
does not like any of the characters
that it is receiving. Another
character is received, it doesn't
'compute', so it again responds with
the prompt characters. Some 42 feet of
paper go by on the TeletypeTM while
you break your neck trying to get
back down-stairs to shut it off.

HARDWARE REQUIREMENTS
1.

33 ASR T e l e t y p e ^ running
full duplex to the computer.
This allows different data
to be input and output in
addition to suppressing output when needed (killing the
echo).

2.

Paper-tape reader under
software control.

This will allow stopping the
reader on recognition of an error.
NOTE: All paper-tape reader
control functions must be strapped
out. Examples:
EOT End of Tape
X-OFF
WRU Who are you (Kicks of
answer-back drum)
Continued
CN/December 1 9 7 6

CMPCTER-LOADER
Masters Paper-Tape Reader
Continued

If received, any of these characters will cause something detrimental
to happen. Pure binary characters
will b e sent to the printer, the odds
of hitting these control functions
are quite high.
Although both the CMPCTER (compactor) program and the LOADER program
exist in the Motorola format, they are
small enough so that you can manage to
get them in even the most finicky
TeletypeTM.
CMPCTER will take your Motorola
style 680 BASIC or ASSEMBLER tape
and compact it to the new binary
format. This needs to be done only
once for each of your big tapes.
The loader must be pre-loaded.
It's entered before the compacted
BASIC or ASSEMBLER tape and is
actually the mechanism that brings
in the compacted tape. The compacted
tape is of a binary nature, so the
LOADER will handle it.
CMPCTER
Let's assume that you want to
compact a particular program tape—the
MITS EDITOR/ASSEMBLER, for example.
It's supplied in the lengthy Motorola
format. The starting address of the
EDITOR is 0107. Remember^ the tape
needs to be^ compacted only One time.
Using the (L)oad command, load
the CMPCTER program via the Altair
PROM monitor. During loading, it
will kill th6 echo, stop the tape
reader at completion and return echo.
Type the letter 'J', so that
control returns to the EXEC.
Load the paper tape to be compacted into the reader, but do not
start the reader yet.

0000.

Start CMPCTER by typing (J)ump

CMPCTER will respond with a
question mark. It's asking you
at what address you want to start
your compacted tape program.
Type in 0107. At the completion
of typing the '7', quickly reach
over and turn-on the paper-tape
punch. CMPCTER will start to punch
out the leader.
When the leader stops, turn on
the paper-tape reader.
What happens next is rather odd.
The computer will read in one block
at a time, stop the paper-tape reader
and proceed to punch out that block
in compacted form. The T e l e t y p e T M
printer will be making rather weird
motions as it's responding to the
binary data fed to it. Every so
often, some ASCII data might even go
b y , but usually it will just type
gibberish. Let it go. It will
CN/December 1 9 7 6

take a while, but let it read and
punch.
Should CMPCTER pick up either
a non-hex character or a checksum
error, it will HALT and will not
continue either reading or punching
data. No problem. Here is how to
recover from the error:
Turn OFF the paper-tape punch.
Turn OFF the paper-tape reader.
Reposition the tape in the
reader to the middle of the preceding data block.
Hit RESET on the computer and
restart CMPCTER at (J)ump 0000.
Turn ON the paper-tape punch.
And finally,
Turn ON the paper-tape reader.
Compacting will then resume.
At the recognition of the 'S9'
data block, compacting will cease.
CMPCTER will then add its own
special data block JUMP mechanism
(7E 0107) to the compacted tape in
order to start your EDITOR program
at 0107.
This will be followed by a
finishing leader. The final thing
CMPCTER will do is list how many
blocks (in decimal) that it has
compacted.
LOADER
COADER is also in the Motorola
format (but it's very short and
sweet). Using the (L)oad command,
put LOADER into the computer.
Position the compacted tape to
be loaded in the reader, and turn the
reader ON.
Start the LOADER program at
(J)ump4300.
The LOADER will take over control
Of tRe reader and quickly bring in
your Binary-mode compacted tape.
The LOADER will respond to two
types of errors. In both cases, the
reader will stop dead in its tracks.
1.
2.

It failed to recognize
a block-mark correctly.
It failed on a computed
checksum.

The format of the error messages
is included on the assembly listings.
To recover from the error:

Yes, fixing the paper-tape
reader would have solved a lot of
problems. As parts become available,
it is being repaired. But the added
bonus of CMPCTER-LOADER is that the
actual load time is cut in half due
to the binary mode of the program
tape.
About the only critical software
item is a constant in CMPCTER, labeled
TIME. It appears once (line#00176)
at address 01EC. This value may need
adjusting depending upon how fast
your paper-tape reader can be stopped.
Even if you do not own the
Altair 680b computer, most microprocessor systems use an ASCII type
of tape data format. Writing a
CMPCTER-LOADER program in the machine
language of your computer will pay
big dividends.
Bits § Pieces
C o n t i n u e d f r o m Page Two

NEW FACES HAVE APPEARED IN THE
MIT5"MIRROR
MITS would like to welcome to
her ranks Ken Zaike, Charles Olsen
III, and David Ning. Ken is now
the head of our Industrial Sales
Department, Chuck is heading up
Public Relations and David now
handles International Sales. If
you have questions in any of these
areas, please feel free to contact
these gentlemen.
RENEWAL SUBSCRIPTIONS ARE NOW BEING
ACCEPTED
For the cost of $5.00/year
($20.00 to our foreign customers),
you will become an Associate Member
of our Altair Users Group. As a
member you will receive a copy of
Computer Notes monthly, plus you
will be able to both write and purchase any programs (for a copying
charge only) which we have in our
Software Library. For payment we
will accept the following: BAC, M C ,
a Bank Check, or a personal check
which requires a 3-week holding
period. We will be sending out
renewal notices in mid January to
all those persons whose subscriptions
will expire after the January issue.
This will allow for the time necessary to submit your renewal order,
and not miss any issues of Computer
Notes.

Back up the tape to the middle of
the preceding data block, and turn
the reader ON. Block marks are easy
to recognize in this compacted form-they are two rubouts in a row (hex FF,
FF).

Those persons who have already
sent in their renewal subscription
in the amount of $10.00, will have
this money remain on their account
until such time that they either
request a refund or utilize the
money for another order.

Reset the computer and restart
LOADER at (J) 4300. Loading will
then resume.

If you have any questions,
please feel free to contact u s .

The last data block on the
compacted tape is actually a JUMP
instruction that will over-write a
part of LOADER and cause a jump to
address 0107. After that, your
program will b e up and running.
Page T h i r t e e n

RDY LDA
STA B
LDA B
STA B
JMPBI
ORG
FCB

$
MAM LOADER
#2.0

*
*
*
*
*
*
*
*

$43FE
0*0

CLEAR BLOCK COUNT

ORG $ 0 0 F 3
FCB $ 0 3
ORG $ F 0 0 O
FCB$B!

*
SOURCE

B #$D!
ACIACS
8 B I T S AND READER ON
#$FF
$F3
K I L L ECHO

LOADER V I L L LOAD IN A PURE B I N A R Y
OUTPUT TAPE PRODUCED BY CMPCTER
THEN JUMP TO A PREARRANSED ADDRESS

GOOF BRA GOOF
* ON A GOOF* COMPACTING W I L L STOP H E R E .
* I T I S CAUSED BY E I T H E R A NON-HEX CHARACTER
* OR A BUM CHECKSUM.
* BACK UP SOURCE TAPE TO THE B E G I N N I N G
* OF THE STOPPED BLOCK AND RESTART PROGRAM

END

ERROR
MESSAGES
BMM # # # # AAAA DD
CVV #### AAAA DD

*
B:
*
C:
*
MM:
*
VV:
* AAAA:
*
DD:
* ####:
*
*

BLOCK MARK ERROR
CHECKSUM ERROR
BUM BLOCK MARK
CHECKSUM VALUE
LAST ADDRESS BLOCK LOADED
CORRESPONDING DATA
BLOCK COUNT LOADED

OPT P
A C I A C S EQU $ F 0 Z 0
BYTECT EQU $ 0 0 F 9
BLKCNT EQU $ 4 3 F E
X H I EQU $ 0 0 F A
XLOW EQU $ 0 0 F B
OUTCH EQU $ F F 8 !
0UT3H EQU $ F F 6 D
OUTS EQU $ F F 8 2
POLCAT EQU $ F F 2 4
ACIADA EQU $ F 0 0 !
NCHANG EQU S F F S F
*
ORG $ ^ 3
FCBSFF

KILL

ECHO

*
ORG $ 4 3 0 0
*
BEGIN
J M P RDY
B I J S R BYTGET
CMP B # $ F F
BMEBI
J S R BYTGET
CMP B # $ F F
BEQ L I S
PAST F I R S T BLOCK MARK?
BRAB!
*
ORG $ 4 3 ! 6
*
* THE NEXT 3 ADDRESSES A R E
* OVERWRITTEN WITH JUMP INSTRUCTION
L D BSR BYTGET
NOP
*
*
CMP B # $ F F
RUBOUTS
M E KB
BSR BYTGET
CMP B # $ F F CHECK NEXT ONE TOO
M E KB
H 3
CLRA
ZERO CHECKSUM
BSR BYTGET
GET BYTECOUNT
SUB B # 2
STA B BYTECT
BYTECOUNT
L D ! I BSR BYTGET GET H I G H ADDRESS
STA B X H I STORE I T
B $ R BYTGET
GET LOW ADDRESS
STA B XLOW
STORE I T
LDX X H I
LOAD X WITH ADDRESS B U I L T
MORE BSR BYTGET
GET DATA BYTE
DEC BYTECT
DECREMENT BYTE COUNT
BEQ L D I 5
DONE WITH T H I S BLOCK?
STA B X
STORE DATA
INX
BUMP P O I N T E R
BRA MORE
GO BACK FOR MORE
L D I 5 INC A
INCREMENT CHECKSUM
LLD
BEQ BUMP
ALL OK
PSH A
LDA A # ' C
CHECKSUM ERROR
BUM LDA B # $ 9 1
STA B A C I A C S
K I L L READER
CLR B
STA B $ F 3
ECHO ON
LDA B # $ 0 D
J S R OUTCH
LDA B # $ 0 A
J S R OUTCH
TAB
J S R OUTCH
DUMP TROUBLE TYPE
PUL A
J S R OUT2H
DUMP BUMMER
J S R OUTS
SPACE
LDA A BLKCNT
J S R OUT2H. DUMP BLOCK COUNT
LDA A B L K C N T * !
J S R 0UT2H
J S R OUTS
* SHOW BUM BLOCK ADDRESS AND RETURN TO PROM
J M P NCHANG+5
*
KB P S H B
LDA A # ' B
BUM BLOCK MARK
BRA BUM
*
BUMP CLC
LDA A BLKCNT*I
M C A
DAA
STA A B L K C N T * '
LDA A BLKCNT
ADC A # 0 0
DAA
STA A BLKCNT
BRALD
*
BYTGET J S R POLCAT
READY YET?
BCC BYTGET
NOPE
LD)A B A C I A D A
GET S B I T CHARACTER
ABA
ADD TO CHECKSUM
RTS

Page Eight

CMPCTER

SETDMP DEX
WHOOPS ONE TOO MANY
STX BUFEND
SAVE END ADDRESS
LDX #BUFFER
GET START ADDRESS
DMPBUF LDA B X
GET CHARACTER
J S R OUTCH
DUMP I T
CPX BUFEND
REACHED END ADD?
BEQ DONE
INX
BRA DMPBUF
DONE CLC BUMP BLOCK COUNT
LDA A BLKCNT*!

MCA

*
*
*
*
*
*
*
*
*
*
*
*

DAA
STA
LDA
ADC
DAA
STA
JMP

NAM CMPCTER
SOURCE # 1 . 8
COMPACTER W I L L TAKE A MOTOROLA PAPER-TAPE
FORMAT COMPACTING I T TO A B I N A R Y FORMAT FOR LOADER
IN A D D I T I O N TO ARRANGING A JUMP TO THE PROGRAM
BEING LOADED
SHOULD AN ERROR OCCUR* COMPACTING
W I L L BE TERMINATE AND CAN BE RESUMED
START AND RESRT ADDRESS

J

0000

OPT NOG
OPT P
*
TIME EQU $ F S

PTRC RELAY

CONTROL

*

BYTE EQU $ F F 5 3 PROM
BUFEND EQU $ 0 0 0 C BUFFER END ADDRESS
BLKCNT EQU $ 0 3 F E
BLOCK COUNT
BYTECT EQU $ 0 0 F 9 BYTE COUNT
SKELAD EQU $ 0 0 0 3 JUMP SKELETON
BUFFER EQU $ 0 0 1 0 TEMP BUFFER
BADDR EQU $ F F 6 2 PROM
INCH EQU $ F F 0 0 PROM
READER EQU $ F 0 0 0 A C I A C S
OUTCH EQU $ F F 8 I PROM
OUTS EQU $ F F S 2 PROM
ECHO EQU $ 0 0 F 3
0UT2H EQU $ F F 6 D PROM
TEMP EQU S 0 0 F 8 .
STAD EQU $ 0 1 0 0
ORG $ F 3 K I L L ECHO
FCB$FF
*
ORG $ 0 0 0 0
START J M P B E G I N
SKEL FCB $ F F * $ F F BLOCK START
FCB $ 0 6 BYTE COUNT
FCB $ 4 3 * $ ! 6 OVERWRITE ADDRESS
FCB $ 7 E JUMP INSTRUCTION
J M P A D R FCB 0 * 0
JUMP ADDRESS
SKLCK FCB 0 CHECKSUM
*
ORG $ 0 1 0 0
BEGIN
J S R CHI-1
J S R CRLF
LDA B # $ 3 B PROMPT
J S R OUTCH
STA B ECHO
TURN ON ECHO
J S R OUTS
CLR A
ZERO CHECKSUM
STA A BLKCNT
ZERO BLOCKCOUNT
STA A BLKCNT*)
J S R BADDR
GET JUMP ADDRESS
STX JMPADR
STORE I N SKELETON
ADD A # $ D D
PRECANNED CHECKSUM
COM A
STA A SKLCK
J S R CRLF
CLR B
NULLS
J S R LEADER
LDA B # ' P
SPECIAL
J S R LEADER
*
LDX#*
STX S T A R T * !
LOOP LDA B # $ F F
STA B ECHO
K I L L ECHO
LOAD LDX #BUFFER
LDA B # $ F F
STA B X
START MARKS
INX
STABX
INX
J S R CHIN
READ FRAME
SUBB#'S
BNE LOAD
J S R CHIN
CMPB#'9
BEQ CONT
CMPB#'!
BNE LOAD
CLR A
ZERO CHECKSUM
J S R BYTGET GET BYTE COUNT
STA B X
STORE IN BUFFER
INX
BUMP
STA B BYTECT
STORE
L 0 0 P 2 J S R BYTGET
STABX
INX
DEC BYTECT
BNE L 0 0 P 2 DONE?
INC A INCREMENT CHECKSUM
BEQ SETDMP ALL OK

A BLKCNT*!
A BLKCNT
A #00
A BLKCNT
LOOP

*
CONT LDA A #9
LOOP COUNTER
LDX #SKELAD
C ! 0 LDA B X
DUMP AND BUMP
J S R OUTCH
INX
DEC A
BNE C ! 0
CLR B
NULLS
J S R LEADER
J S R CRLF
LDX #STAD
SET TO START NEW TAPE
STX S T A R T * !
LDA A BLKCNT
LETS DUMP BLOCK COUNT
J S R 0UT2H
LDA A BLKCNT*!
J S R 0UT2H
*
HALT
BRA *
*

COMPACTED

LEADER
LDA A # $ 3 2 LOOP COUNTER
L!0
J S R OUTCH
DEC A
DECREMENT LOOP COUNT
BNE L ! 0 DONE?
RTS
*
BYTGET BSR HEXGET
GET F I R S T HEX D I G I T
ASL B
S H I F T TO H I G H ORDER 4 B I T S

MLB

ASL
ASL
ABA
STA
BSR
ABA
ADD
RTS

B
B
ADD TO
B TEMP
HEXGET
ADD TO
B TEMP
RETURN

.

-

.

.. ..

CHECKSUM
STORE D I G I T
GET SECOND HEX D I G I T
CHECKSUM
COMBINE D I G I T S TO GET BYTE

*
HEXGET J S R CHIN
GET CHARACTER
SUB B # ' 0 HEX?
BMI GOOF NO
CMP B # $ 9
BLE BACK
OK
CMP B # $ ! !
BMI GOOF NO
CMPB#$!6
BGT GOOF
SUB B #7
I T S A LETTER GET BCD
BACK RTS RETURN
*
WAIT PSH A
PSH B
LDA A # T I M E
W2 CLR B
W!
INCB

VALUES

MEW!

INC A
BNEW2
PUL B
PUL A
RTS
*
CHIN LDA B # $ D !
READER ON
STA B READER
BSR WAIT
J S R INCH
PPH B
C H ! LDA B # $ B ! ,
READER OFF
STA B READER
BSR WAIT
PUL B
RTS
*
CRLF LOA B # $ 0 D
J S R OUTCH
LDA B # $ 0 A
J S R OUTCH
CLR B
COM B
J S R OUTCH
J S R OUTCH
RTS
*
ORG $ 0 0 F 3
FCB $ 0 3
*
ORG $ F 0 0 0
FCB$B!
END

CN/December 1 9 7 6

Letters to the Editor,
Continued

input signal (SINP) is of importance—during M3 of the input instruction, SINP goes high enabling
circuitry that allows data from the
I/O card to be input during T3.
SINP goes low again at the next
coincidence reflecting a different
instruction. To further set the
stage, during each of the machine
cycles the processor outputs an
address (either for memory or I/O)
which is presented less than 300
nsec. after the start of that
machine cycle or about halfway
through Tl. The problem occurs
during Tl of the RRC instruction,
because the coincidence of SINP and
the address for that instruction
(which happens to be the data
channel address) resets the "data
available" FF in IC M—pin 19 on
the I/O card. As written, the
program will then cause a reset
pulse of 200 nsec. at pin 8 IC G
(SIO-B) during Tl of RRC every time
through the loop. If the "data
available" FF is set after the
status word is input from IC M
during T3 of M3 but before the
reset during Tl, then the indication of a character present is
lost as well as the character itself. Normally, the reset doesn't
occur until the input instruction
at location 007 is executed with
the data channel address. In that
case the character is input and the
"data available" FF is cleared to
indicate that fact.
This situation will occur
with the use of the SIO cards and
the ACR and possibly with other
I/O cards. While a hardware solution is not crucial to the operation of a system, it could be
unwieldy to use interrupts or write
programs in specific locations,
particularly if the number of I/O
cards were increased.
Sincerely yours,
Jim Wiggins

Attair
Users
Don Chamberlain
9457 Las Vegas Blvd. South #321
Las Vegas, Nevada 89119
Phone: (702) 361-4924
Alfred R. Howes
Box 342 Boyce Rd.
Glenford, NY 12433
Dick Fehriback
5779 Blaine SE
Grand Rapids, MI
(616) 455-3138

CN/December 1 9 7 6

49508

HAM .

on the side
By Dave LeJeune

Paused LeJeana
a Lcaate^a^t
CoZoHeZ
t^e AAMt/
CoAjas.
Ha gAac^ou^t/
to -ta&e. oveA
M M CM THE 3IPE.

Ignoring a long-standing policy
that I picked up early in my Army
career to never volunteer for
anything, I now find myself with a
monthly column to write about the
marriage of amateur radio and
computers. My appeal goes out
early—HELP! From the great amount
of chatter I hear on the ham RTTY
nets, the C.W. bands and the voice
frequencies, I assume that there are
a lot of hams out there playing
around with microprocessors. This
column offers all you enthusiasts
the perfect opportunity for letting
everyone else know what you're doing.
The success of this column depends
upon reader acceptance, and that's
measured by the amount of feedback
(good or bad) you give me. So start
sending those cards and letters now!
I've been a ham for about 20
years, so I'm old enough to remember
the changes caused by the introduction
of single side band(SSB) to our
ranks. SSB completely revolutionized
HF voice operating. But, as often
happens with many new products,
people didn't fully accept SSB
at first and simply termed it a
new fangled device. Within 10 years,
however, it had become the dominant
mode for voice communication. In the
mid 60's the re-introduction of FM
(it had been used by many for a
short time immediately following
WWII) had the same effect on the VHF
bands.
The use of repeaters caused this
mode of operation to spread like
mad, and today, most cities where
more than two or three hams reside
have some sort of VHF repeater
available.
The introduction of the
microprocessor had the same effect
on amateur radio as the introduction
of SSB and FM repeater techniques.
The microprocessor can be used for
such applications as RTTY and C.W.
as well as station control, logging
and contest operating. However,
with a little help from the FCC,
the microprocessor may also find
its way into voice operating.
In the commercial communications
field the trend is towards a total
digital network. With such a
network it's easier to multiplex
many digital channels onto a single
transmission system than to analog
channels. Designing circuit
switches is also easier. But many

problems have yet to be solved.
For instance, if voice
recognition is to be maintained, a
digital voice channel must use twice
the channel bandwidth as a comparable
analog channel. The channels should
require about the same bandwidth
for a given power level and signal-tonoise ratio. Other areas in the
development of optimum error
detecting and correcting codes are
still wide open to exploration and
experimentation. The only tools
needed to attack such problems are an
amateur radio station with some
means of generating the necessary
digital voice, RTTY or C.W. signals,
a microcomputer and some means of
interfacing these two systems.
As mentioned previously, the
FCC needs to help out by easing
current regulatory restrictions
imposed on amateur radio operators.
As a starter the restriction of
RTTY operation to the Baudot code
should be removed. This would bring
the RTTY ham out of the dark ages
and into the world of computer
communications. Secondly, in order
to attack the problems of digital
voice transmission and error
correcting codes, the restrictions
prohibiting the transmission of
codes and cyphers should be removed.
The FCC has recently released a new
proposal(the "bandwidth" proposal)
which will help lift these and other
restrictions that currently limit
our ability to experiment over the
air. However, the proposal seems to
be hung up somewhere within the
FCC. A note to your congressman
might just be the thing to spring
it loose.
I would like to discuss these
and other topics of interest to
the ham/computer freaks in future
issues of C.N. Interested readers
can once again communicate with me
via the MAILBOX system(channel
14.075000 mhz) described in last
month's C.N.(It went off the air
temporarily in November while the
system was being upgraded to an
Altair 8800b.) Or, you can just
as easily drop me a note in care
of C.N. to let me know what sort
of information you'd like to see
in this column.

Page Thirteen

S!V!ALL

By:

C O M P U T E R
N E T W O R K I N G

B)G STUFF

Bob Matthews

Two news items from the
October-November issues of
Datamation are indicative of two
major, but seemingly opposite, trends
in computing: the move toward bigger,
more efficient computers and tEe
trend toward smaller, more efficient
computers.
In one of the news items
(Datamation, Oct. 1976, p . 17), the
Los Alamos Scientific Laboratory in
New Mexico announced the delivery of
its new supercomputer, which can execute over 20 million floating point
operations in one second! (But who's
counting?) Obviously, the potential
capabilities of such supercomputers
are still being explored, and more
such developments are certainly
forthcoming in New Mexico as well as
other states.
The second news item (Datamation,
Nov. 1976,p. 17), notes that a bank
in Boston has cancelled its order
for several moderately large computer
systems. The cancellation was due
not to lack of money, but the bank's
decision to convert its original order
into an even larger order for 200
minicomputers. The bank figured it
can accomplish things more efficiently and economically with a system of
small computers rather than with a
few large computers. The bank says
that within three years there won't
be anything larger than a PDP 11/70
in the house.
The bank in Boston isn't the
only institution that has opted to
disperse its computing power throughout the organization. Business,
scientific laboratories and educational institutions are also tying
their computers together in networks
to allow small computers, working
in tandem, to do the work of big
computers. (See Digital Design, Feb.
1976,pp.26-27; IEEE Spectrum, July
1976, pp.91-93; Business Week, July
5, 1976, pp. 38-447)
A few examples will show some
of the capabilities of distributed
processing in the hands of a small
system user.
A. A Minimal System. User A
is a graduate student in astrophysics and is doing a research in
stellar structure. This research
requires the solution of some fairly
complex differential and integral
equations, most of which have no
analytic solutions. The numerical
solutions to these equations require
huge amounts of raw computing power
but relatively little input/output
sophistication. After crunching
numbers for several minutes or even
hours, the computer might only print
Page Ten

a few pages of numbers and a graph or
two. Since grant money is limited
these days, especially for theoretical astrophysics, User A needs
a low-cost system that has modest
I/O facilities, program storage and
editing facilities and enormous floating point mathematical power. Until
recently, no system combined all of
these capabilities. But now with the
age of distributed processing, a system
for User A might look like this:

Modem

telephone
to big
computer

Altair
8800b

would also create more space on
A's desk, which otherwise would be
overflowing with reams of printer
paper and card boxes.
A's system has plenty of speed
to handle the CRT terminal and the
phone line simultaneously, but there
isn't much time left over to do
computing on the data as it is being
shifted around. If more computing
time is necessary, and A , for example,
wants to change the format of the
data or apply some relatively simple
calculations before it is sent to the
big computer, one of two things must
be done. Either the software must be
written to allow interleaving the
tasks of I/O and computation, or
the following modification must be
made to the hardware.

CRT terminal
Figure A

The heart of the system is an
Altair 8800b microcomputer. It controls a CRT terminal, a printer, small
plotter and a floppy disk unit. It
is connected through a dial-up or
private U n e to the university's (or
whoever's) computer center. A's big
simulation program, which A's supervisor and his colleagues pieced
together over a period of years and
to which A has been making modifications all along, is stored on a
floppy disk. The program can be
loaded into the supercomputer through
the telephone line. To make any
necessary changes, A can use the
text editor, which runs on the
Altair computer, and either save the
resulting code on disk or send it to
the big computer to be executed.
Once the program is loaded, A can go
home (or more likely, to the library)
and let his Altair system handle the
housekeeping details. ' It can log
intermediate output, error messages
and even provide input for the big
program when it is needed. Finally,
it can receive the output of the
program and store it for later recall.
When A comes in, the output can be
examined or "massaged" to make it
easier to handle, or the error message file can be examined to see
what went wrong.
This is a brief example of a
simple system, but it illustrates
how the intelligence of an Altair
8800b could be used to help A's
research along by allowing more
time for studying instead of running back and forth to the computer
center. Such a system would allow
more flexibility in changing the
program and data around to fit the
requirements of the project. It

Printer/
Plotter

Altair
8S00b
#2
(COMPUTE)

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Altair
8800b

Modem

(I/O)

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