AGR Microcontroller
A Ben Eater-inspired 8-bit computer, built from the ground up: starting with individual transistors, then logic gates, then latches and counters — slowly assembling previously-built modules into a full working system.
The approach
Nothing here is a pre-built chip standing in for the interesting part. Every stage is built up from the one before it, on breadboards, before it earns a permanent module:
Bottom-up build order
- Transistors — the switching behavior everything else is built from
- Logic gates — built from those transistors, not off-the-shelf
- Latches & flip-flops — the first bit of memory
- Counters — the program counter's ancestor
- Registers & the activity register — holding state between clock edges
- Full modules — program counter, program memory, and beyond, combining everything above
Why build it this way
- Every module is understood at the transistor level, not just wired in from a datasheet
- Bugs get found at the layer they're introduced, not three modules downstream
- It's the same reason Diagno exists — a build like this needs a tool that can watch a full bus, not just one pin
Build log — modules so far
A running gallery of the modules built and tested so far. Full write-ups for each are on Instructables (linked below).
Sponsors
This build runs on parts and boards from people who backed it before it was proven out.
Eleshop.eu was one of the earliest supporters of this build, back when it was just breadboards and a plan. I went quiet on the project for about three years — that gap was on me, not them, and this build log exists in part to make that right. Thank you for backing this before there was anything to show for it.
PCBWay manufactured the Program Counter module's PCB and delivered prototypes that turned a breadboard design into a real, permanent board.
NextPCB supplied the Program Memory module — turning that stage of the build from a rat's nest of breadboard wiring into a proper board.
ZeroPlus — the logic analyzer that's been essential for watching this build's buses, supplied through Eleshop.eu. It catches exactly the kind of multi-line timing issues a single probe can't.