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A project log for The 74's called ... (SUBLEQ)

Yetanother simple CPU of TTL chips.

Michael MöllerMichael Möller 04/13/2020 at 10:470 Comments

It started about 3 years ago with viewing the Ben Eater series on building a simple CPU with just breadboards and TTL. Although the 74's are "relativly cheap", there are lots of them, and the total expenditure kept me back. Ben Eater sells the kit, but that makes it a boring repeat. In autumn 2019 I bought a selection of chips, both to cover that project, and a "suitable" selection of others, and a few to spare.

I want to experiment with the challenges of of doing my own. I know the architecture of CPUs as such, so this is purely fun, as a puzzle. I want to extend the BenEater design with more RAM, an IO subsystem (keypad input, Serial?), something to load RAM, Interrupt handling, and paging. Of course at that point it isn't a "simple CPU" anymore.

As the title picture shows, I have constructed a tray so I can easily take it out to play, and put it back even in mid work. On a wooden base I have a large conductivefoam area to store chips, there is a 5V supply,  and an Arduino to act as a test generator, and bulk storage IO device. Breadboards obviously, and a strip-board bus in the middle (rather than using even more breadboard)

"Walk before you run" - so this first project on my CPU constructor kit simplifies CPU capabilities even further: One instruction, avoid "bus"/Tristate, start with 4bit (address and data).