I know I literally just said that the next log would be about the address decoder, but then I remembered I've been meaning to write a quick log about the EEPROM programmer I hacked together for the m68k project, so here's that instead.
(TL;DR - It's on Github: https://github.com/roscopeco/eeprom-programmer)
Once the address decoder is built, I'm obviously going to need to program the EEPROMS for the m68k build. I could go the easy route and just buy one, but I decided I had enough stuff lying around that I should be able to hack one together. It turns out I did, but I had to make some, ahem, compromises to make it work.
Quoted from the README on Github:
This project uses an ESP8266 dev board (NodeMCU 1.0) along with three 74LS174 hex D-flip flops to program the 64 Kbit EEPROMs I'm using in my m68k breadboard computer. The choice of components may seem a bit odd - the design was driven entirely by what I had available on the bench at the time, and my being too impatient to wait for a ten-quid programmer to arrive in the post. So I just hacked this together quickly to tide me over.
So basically I just built a shift register driven by the NodeMCU and then used some of the spare GPIOs to drive the W/E line on the ROM. Obviously I could have used shift registers instead of the flip-flops, but I didn't have any.
I'll say no more about it here, it's well documented on Github and the code is there too. So I'll just post a picture of it and move on to address decoding (for real, this time).