Motorola MC6802 repro (early 80s)
Posted: 19 Nov 2020, 00:38
Another 'lockdown 2020' Retro-Computing project
Back around 1980 I worked in BT's Measurement & Analysis Centre, which was a GEC2050 computer that made test-calls and collated results to improve the telephone service. In each exchange, as part of this setup was a TRT302 printer, which contained a 6802 microprocessor board, which we robbed from any faulty printers. I was a Z80 user and this was my first 6800, but I hand-wrote a monitor for it and me & pal Steve made development systems from these boards. 40+ years on, I still have that original board, but its forever breaking and I thought I'd make a reliable reproduction using the same hardware and the same monitor program. It has display memory, modify memory, goto program, a serial loader for 'S' records, breakpoint & register display, NMI handling etc... quite complex for a hand-coded project in 1980. The Repro is much smaller and neater but works exactly like the old one.
The original display on the TRT board was intended to use two TIL311s but they turned out to be too expensive in 1980, hence the homebrew eprom & calculator display arrangement. Today I have a few TIL311s so thats what I used - much neater! I need to find some more, they're so useful.
The noughts-&-crosses game is embarrassingly simple by todays software standards, but its typical of hand-coded, amateur efforts back in the day - of course, its unbeatable, it may be over 40 years old but it never tires of winning!
Getting a micro to play a tune, or to calculate prime numbers was an achievement back then, this was all fascinating new territory for the electronics hobbyist.
Cheers
Phil
Edit: just realised this isnt number 4, its 5 - I forgot the mini CP/M board !
Also, I overestimated the age of the original - it was early 80s, not '78 as I first guessed.