[Jeff Tranter] has done a number of retrocomputing projects. But he wanted to tackle something more substantial. So he set out to build a 68000-based single board computer called the TS2 that he found in a textbook. He’s documented it in a series of blog posts (about 30 posts, by our count) and a video that you can see below.
The 68000 had a very rational architecture for its day. A flat memory space was refreshing compared to other similar processors, and the asynchronous bus made hardware design easier, too. While most CPUs of the era assumed bus devices could perform their service in a fixed amount of time, the 68000 used a handshake with devices to allow them to take the time they needed. Most other CPUs had to provide a mechanism for a slow device to stall the bus which was complicated and, in many cases, less efficient.
[Jeff] used KiCAD with an autorouter to lay out some PCBs and all his files are available on GitHub. [Jeff] is actually on his second version, and has substituted some hard-to-find parts with easier-to-source replacements. The detail in the postings is impressive, and the TS2 recalls a time when you couldn’t get your entire system in one IC package.
You didn’t hear it here, but a lot of 68000s escaped into the wild with some defects that affected very particular instructions. For example, if you have one, try doing a long quick add (ADDQ.L) to any indirect address register. It might work, but there is a reasonable chance the CPU will hang mysteriously. In those days, there was no firmware upgrading, either.
We’ve seen 68000s on a breadboard. We’ve even seen the 8-bit version dominated by an Arduino. It would be interesting to see what a modern PC would be like if the 68000 architecture had won the day back them. But we’ll never know.