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S > SCIENCE FAIR > Microcomputer Trainer   

Microcomputer Trainer

Peter Crunden-White, the proud owner of this Microcomputer Trainer, sent us some photos along with the following note:

In about 1986, I purchased a Science Fair Microcomputer Trainer (MCT) from my local branch of Tandy (in Cheshire, UK). The machine was sold by Tandy shops, it was one of their 'wire-it-yourself' project kits and ran on 6 penlight batteries.

I recall that my older brother wired it up for me, but we never really had much success with it, although we enjoyed playing the built-in games (including tennis and rat-bashing) and programming tunes in. Ironically, it wasn't until years later that I actually had any success programming it.

It had a set of about 30 commands (15 simple, plus some 'extended'), which were entered through the keyboard. The keyboard suffered badly from switch bounce; increment would sometimes be registered twice, causing much annoyance.

The CPU (or rather MCU – Micro Computer Unit) was a Texas Instruments TMS1100. This was an expanded version of their flagship "computer-on-a-chip"; the TMS1000, which was used in their "Speak and Spell" toy. According to the MCT manual, the clock speed was 400kHz – but this is higher than the specification for the chip! (Were Science Fair guilty of over-clocking!?!). Presumably the monitor was burnt into ROM – the 30 commands the end user uses being interpreted.

There was no bulk storage: programs were lost when power was removed, so had to written down manually. (I did consider driving the keyboard from my Sinclair Spectrum so I could save/edit programs before 'downloading' them to the MCT, but never got around to it).

The most fun I had with it was when I wired three address LEDs to control a toy drum machine. I then wrote a program that would play an eight-note tune (wow!) in time with a beat from the drum machine.

The manual contains instructions for the built-in games and example programs (complete with flowcharts). Some of the example programs are quite complicated (given how tedious entering them would have been). A ‘Slot Machine’ game comes with a disclaimer: This “slot machine” behaves very much like those that you see at amusement arcades. But you can only play it for fun – the Microcomputer Trainer has not been programmed to give cash prizes. – no kidding!

Javier Perez comments:
I think they overclocked the TMS1100. I checked the internet and it's top speed was 300khz it was an expanded version of the TMS 1000. Made in early 1975 it's memory was ROM 2KB RAM 64 bits. It was a PMOS or MCU . it took 43 standard instructions and 1024 micro instructions.So truly i think they overclocked it by mistake or to sell it but anyone i've only had a chance to see one open but not play with it.tooo bad looked intresting.

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Sam (UK), Interesting the way that you describe this trainer''s method of simulating a simple 4-bit microprocessor. I think this may be one of the simplest examples of what we call a bytecode interpreter. This is the technology that famous languages such as Smalltalk and Java are built on top of. $)

Monday 27th June 2022
Carl Gundel (United States)

Sorry to double-post but... Duncan, that video of yours is certainly interesting! Kind of weird but I suppose instructive to have the user, some naive kid, have to wire up stuff like the display, that should be connected permanently.

Then again... there were only so many I/O pins available. Were there any experiments in the manual with connecting up to other circuits? Did it come with other components? Maybe a tie-in with the other Science Fair kits would''ve been good. So you could connect the computer to other circuits and have it do... stuff. Since it is a MCU trainer and that''s what they''re supposed to do. If you wanted to really learn programming you''d be better off with a BBC Micro or ZX Spectrum with an assembler and a decent book. "ZX Spectrum Machine Language For The Absolute Beginner" by William Tang was great. Started off explaining memory locations as cardboard boxes with numbers written on bits of paper in them. You know the drill! But pretty quickly moved to writing real programs and interfacing with the operating system.

This little box of tricks is a great curiosity but to be honest I think would have disappointed a lot of kids. For less money you could get a box that''d let you control relays and read switches from a computer in BASIC or machine code. The BBC and Commodore machines had built-in user ports for just that, the BBC even having an ADC!

You''d be able to get a lot more done, and learn more about the subject, like that. Of course you''d need the computer too but you''d want that anyway for the games!

Friday 21st February 2020
Sam (UK)

Tor, I imagine the LEDs aren''t labelled in binary for two reasons. One is simplicity and user-friendliness. The other is that the TMS1000 didn''t expose it''s bus to the outside world. Only a few I/O ports, like an Arduino or other microcontroller, since it is a microcontroller.

Sounds like this thing ran a sort-of "emulator", interpreting a program written in a very terse binary format. Could a TMS1000 switch to running code from RAM? I don''t think it could since RAM is 4-bit and I think code was 8-bit. So that would leave storing the program in RAM and interpreting it.

It''s fair enough, it still gives an impression of machine code programming, and is probably less mind-bending than the TMS''s own ASM would be! 48 steps! Just enough for 1 or 2 loops to do a bit of beeping.

A user couldn''t program the TMS series. Instead your company, that was making an alarm clock or calculator or whatever, would write the program in a text editor on a minicomputer or mainframe. Stacks of cards are mentioned although hopefully that''s just as an abstraction!

Then your programmer and TI would work together to ensure it would work, and test it on a software emulator. Eventually, when it was ready, TI would make a mask and produce you a few prototype chips with your program in the ROM, real immutable ROM.

If that went well, it went on to production and off come your thousands of chips!

The chip was like many MCUs intended for calculators, etc, in that it had some support for LED or VFD displays built into the hardware. So you wouldn''t have to bit-bash as much as you might with a modern MCU. OTOH a modern MCU does very well at bit-bashing, with onboard timers, counters, and a high enough clock speed to be able to do all that.

I wonder about stuff like Astro Wars and the many other VFD home arcade games of the early ''80s. As well as the LED and LCD ones. But VFD mostly cos they were so interesting, and produced the best display for a game.

Were these 4-bit? Must''ve been hell to program! Or at least you''d need to be very methodical and keep everything organised on paper, doing actual coding in small blocks that fit to the plan. Or did they use 8-bit MCUs? Were PICs about then?

Some of the early LCD games I think would''ve worked as custom state machines. And there were dozens of cheap ones where the gameplay was identical, only the LCD was changed, from aliens to horses and cowboys.

The early Nintendo programmers, I think Gunpei Yokoi, RIP, talked about re-purposing calculator chips to produce Game And Watch. Each screen element was a unit that would otherwise have been a segment of a 7-segment number!

Anyway... interesting machine!

Friday 21st February 2020
Sam (UK)


NAME  Microcomputer Trainer
TYPE  Home Computer
YEAR  Unknown
BUILT IN LANGUAGE  Assembler-style mnemonics, entered as hex codes
KEYBOARD  20 keys (hex 0-F, reset, run, increment and address set)
CPU  TI TMS-1100 an expanded version of the TMS 1000
SPEED  400kHz?
RAM  128 nibbles (only 16 addressable from user program, some used by operating system)
ROM  Unknown
TEXT MODES  7 LEDs showing address, 7-segment LED showing data
SOUND  Built in speaker producing 'beep' tones & effects
OS  Hexadecimal monitor
POWER SUPPLY  9V DC (6 AA batteries)
PRICE  About £18 in 1986

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