My Homebrew 68000 System

While studying at the University of Stellenbosch in 1987 I built a 68000 computer system. I had very little resources, i.e. I could only get single-sided PCBs made, it was difficult to arrange access to equipment like a logic analyser or digital oscilloscope, even an eprom emulator was out of the question. All of these factors influenced the design.

The system ended up as three separate Eurocards (100x160mm) with DIN41612 A/C connectors. The bus pinouts were chosen to minimise routing problems. All PCBs are single sided, with parallel vertical wire jumpers on the component side. PCB layout was done using smARTWORK.

Card 1 : 68000, Interrupt logic, clock, buffers on all data and address lines.
Card 2 : 64K ram, 192K rom (total of eight 256 kbit devices). This card contains logic to map the rom to $000000 for the first 4 cycles after RESET. This allows the processor to pick up the reset vectors, while the bottom 64K of the memory map contains RAM during normal operation.
Card 3 : 2 x UARTS, Parallel port, Timer.

The software development cycle was fun. (OK, so I'm a masochist :-). I used to write assembler code, hand-compile it, type it into a PC, burn two EPROMs, and then take the EPROMs home and stick them in the system. Single-stepping the 68000 is easy since the whole chip is CMOS. The 68K will wait for the data acknowledge signal DTACK forever. I wire-wrapped a fourth card with LEDs on all data and address lines, and a flip-flop wired to a switch to take DTACK low for one cycle at a time. I got a small monitor working this way, but I wouldn't recommend it :-). I also typed in a crossassembler (in Modula 2) from Dr. Dobbs, and wrote my own disassembler in C. Eventually I got hold of a copy of Dr. Dobbs Tiny Basic for the 68000, which works great. I wanted to put Forth on there, but I got busy with other things, so it never happened.

Some day I might resurrect this system and make something like Peter Stark's SK*DOS run on it.

[Image] Hit Count
hits since 1999-05-27.

Back to Wouter's 68000 Page (This page last modified 2004-02-10)