I decided to start by developing the AVR-based programmer for a couple of reasons. Firstly, I’m somewhat more familiar with AVRs than z80s. Secondly, the z80 parts will be much easier to develop if it can be done without ripping the eeprom out all the time.

It’s coming along nicely, despite some infuriating bugs and kinda awkward birds nests of address lines on the breadboard!

I still intend to try using some shift registers on the address and data lines, but I’ll get it working without then look into that - it should be a relatively simple code change once I get the wiring sorted.

Next I need to write something to receive dats over serial and write it to the eeprom - I’m thinking it might make most sense to just send intel hex format over serial. I actually have some software flow control implemented, so hopefully I won’t lose any bytes!