Vintage Computer Mark 8 Microcomputer Copy by Roy Justis
My Blog/Virtual Museum http://www.microcomputermuseum.com
I first learned to program a computer by taking a class at
Virginia Tech which taught Fortran IV on the IBM370 main frame
using punch cards for data entry. The year was 1978 and it was
an enjoyable class. We worked at our own pace and graded on
our mastery of the subject as measured by how many programs
we completed and how well we solved the problem in logic given.
Then came video terminals in place of the punch cards for a chemistry
class. Very cool stuff. I spent many late hours at those old HP terminals running simulations of NMR spectra and chemical composition
Subscribe to my Channel David Larsen LCF Group http://www.youtube.com/subscription_c... I left Tech in 1980 and took a job as a lab technician and operator at
a local waste water treatment plant. I wasn't seriously going to take the
job at first but I went to check it out anyway. When I got there I talked to the superintendent and looked around. I walked into a room filled with
analog controllers, strip chart recorders and alarm systems and I
changed my mind about taking the job. It was a fine opportunity to learn
more about process control and analog electronics. I went back to tech in 1984 and took some digital electronics classes
taught under Mr David Larsen and Dr. Paul Field. Just about that time the
plant I worked at began to be upgraded with digital electronic controllers
and we received our first IBM PC. Actually it was a Radio Shack
model 1200 which was an accurate clone. I spent the next year
writing the software we used for processing the data we collected
throughout the plant. We used this software for about 14 years
until we upgraded to a windows system and had to purchase a
professionally written program to replace my homebrew software.
The classes in digital electronics and computer programming at
Virginia Tech prepared me for the transition from analog to digital
electronics and for the use of computers in the lab. I first heard of the Mark8 when I saw an Ebay auction for a kit to build the
machine in the vintage computer hardware category. I started reading about
it and to my astonishment learned it was built by a guy from Virginia Tech.
I myself attended Virginia Tech in the 70's and 80's and hadn't heard about
the Mark8 until this time (2006). I also read that most original Mark8 kits sold
did not result in operational machines because of its complexity
so I decided to try my luck with it. I purchased two of the kits which
contained the PC boards and a few critical components and set to work
on the machine. After a couple of weeks stuffing the boards and constructing
the framework they resided in, I completed the enclosure, wired up the
switch banks to the PC boards and completed all the miscellaneous connections
necessary for operation. When I applied power nothing happened. After
some investigation with a logic probe I found a dead chip and replaced it.
I also had to replace three flip-flop circuits and powered up again. IT WORKED!!
Couldn't believe my luck. The next task was to run the test program provided
in the original magazine article. I input the program and set the switches and
the machine began to execute the test program. Everything worked and
the output register began to count in binary from 0 to 255 then cycle back to
zero and start again in an endless loop. The machine was alive and I had
a fully functional Mark8 on my hands! Building the keyboard was the next step. I nabbed a couple of ASCII
keyboards off Ebay but couldn't get them to work since they didn't have
any documentation with them. I finally found a basic matrix keyboard
complete with schematics and used that in conjunction with a microcontroller
to produce a fully functional ASCII keyboard. I also programmed the
microcontroller, an Atmel ATmega16, with some custom Mark8 software
that it could transmit to the machine after a 17 byte boot-loader program was
manually entered into the Mark8.
That is how I came to know the Mark8. The machine that started the PC
revolution we live today....
Roy R Justus
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