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EDUC-8

An 8 bit micro-computer designed by Jim Rowe.
Description and construction details were published in a series of articles in
Electronics Australia starting in August 1974.
It was built entirely from TTL components, had 256 bytes of memory and supported a number of external devices.

Articles can be found about it at
http://www.ljw.me.uk/educ8/educ8.html ,
http://www.sworld.com.au/steven/educ-8/ and
http://en.wikipedia.org/wiki/EDUC-8 .

Last updated 16/08/2014


Photo 1

EDUC-8 built around 1975 and mounted in a space-frame to keep it all in one piece. 

Back in 1974, I had been working in IBM for 4 years and, although I had learned much about system design and programming, I didn't have a clue about how a computer performs its tricks, so Jim Rowe's EDUC-8 was the perfect project to find out. It served its purpose well. Jim's articles and the resulting device were sufficiently low level that one could understand exactly what was going on inside when each of the logic unit "tricks" was executed and how these were strung together to form a program. I regret now having sold the final working system with all of its documentation as it would be interesting to relive the experience. I owe a lot to that low level knowledge. You just cannot get it from a modern computer-on-a-chip IC.

I purchased the boards and most of the components from a parts supplier in Redfern (he did quite well out of me) and started construction. Being made of basic logic ICs and a few discrete components on single-sided boards plugged into a front panel, it was quite easy to build for someone with moderate soldering skill.

It soon became apparent that having to re-enter a program, instruction by instruction, from switches on the front panel was a bore, so I built a UART interface to a compact cassette recorder. A small utility program saved everything in memory to tape. So all I had to do now, when I turned it on, was to enter another small utility on the switches to read from tape to memory and, voila, I had a rudimentary Tape Operating System. I don't remember from where I obtained the tape interface, but it was probably another of Jim's designs.

That was great and I had fun for a while entering data on the front panel and reading the results on the LEDs. It still amazes me how much could be achieved in just 256 BYTES of memory with very careful and efficient code design. 15 - 20 years later, by the end of the 80's and certainly by the mid 90s, anything less than 256 MILLION bytes of memory was considered the absolute minimum and by 2012 the standard was at least 2GB. Modern machines are so fast and the memory so vast that today we generally don't care if the code is inefficient. More's the pity.

The next challenge was to add a terminal interface with keyboard and screen. Once again, the design probably came from Jim's pen.

Thinking back now, the remarkable thing was that, with all those components, jumpers, interconnecting wires, plug in boards and my moderate soldering skills, each board and the system as a whole worked first time. I didn't have one component or board failure in the time I owned it. Full marks to Jim Rowe for a thoroughly well designed and sorted project.

By now, the birds nest was becoming unmanageable and needed tidying up (she who must be obeyed probably had something to do with this), so I built an aluminium space-frame to hold it all together so that it could be hidden away in a cupboard when not in use. It never did have any covering panels so it was a good idea to keep small fingers, or large ones for that matter, well clear of the power supply when it was on and for a while after it was switched off until the charge on the capacitors had leaked away.

The keyboard, its interface and the terminal interface was mounted on a frame that hinged down so that I could get at both sides of the components. Looking at the photos now, my scrawl on the frame suggests that the two switches on the left were for Half/Full Duplex and TTY/Terminal mode but the one on the right is illegible. It looks like it may have been a 3-position switch - one position is definitely marked OFF but I cannot read the rest. Perhaps, if you built the same boards, you can tell me what it is likely to have been as Photo 4 with the keyboard hinged down shows wiring from it to the small grey board adjacent to the keyboard on the right of the sub-assembly.

The photos at here were scanned from 35mm slides; sorry for the meagre resolution. Click the thumbnail to see the full sized version.

Well, there it is; a piece of history which kept me off the streets for quite a while, building and playing with it and providing me with valuable background knowledge. In the end it had to go when I bought a "Trash-80". I sold it to a Uni professor who needed a teaching aid in a computer class. I sometimes wonder if it was useful and if it still exists somewhere in a dusty cupboard; I doubt it; probably thrown out long ago. The TRS-80 too was sold and replaced with a succession of PCs but for fun, Geoff Graham's little miracle, the MaxiMite, is my current obsession. Back to fun(damentals)... and BASIC... bliss (-:
 



Photo 2

A view of the User interface.
 


Photo 3

The daughter board on the left supported a compact tape player to store and retrieve programs.



Photo 4

The terminal unit hinged down to give access to the circuitry and showing the 3 switches beside the keyboard.
 



Photo 5

The power supply, which can probably now be replaced by a single pug pack!