[Donn] wanted know exactly what is going on inside of a processor so naturally he built a CPU out of TTL components. He had previously built a couple of versions of a computer based on the Z80 processor. Using the troubleshooting skills he learned and a second-hand textbook, he set to work using 74LS series chips connected using the wire-wrap method we’re familiar with from other cpu projects.
The finished product runs well at 1.8 megahertz, but he also included a 2 hertz clock and a step clock for debugging. At the slower speeds, the register board (seen at the left in the picture above) lights LEDs and can be used to tell what the CPU is currently working on. Programming is accomplished through either a dumb terminal or a PC running a terminal emulator.
His writeup is from about five years ago but that didn’t prevent us from getting that fuzzy feeling in the geek-center of our brain when we read about it. It is well written and thorough so if you’re into this kind of thing there’s plenty to enjoy.