ROMs are based on M5M27C101JK, which he said is EPROM. I'm not seeing a datasheet for that, or any that are similar enough, so just I'm assuming that this pin is a /WE. Most modern 32-pin ROMs have the same pinouts. I guess it's possible that this pin is NOT a /WE. These ROMs are ~20 years old. There is also another pin connected to a +5V supply that usually is NC. MAYBE this is actually /WE. I'm not sure.

Click to expand...

The pinout for memory chips is a JEDEC standard, but that may have been before the standards. The '27C' series is EPROM for every manufacturer with which I am familiar and the M5M would make it a MItsubishi part number. Up until about seven or eight years ago they had the datasheets up on their website, but they took them down a while back. Sigh. Similarly for Toshiba.

A line tied to 5V would make more sense as the WE pin. I think there was a Vpp pin (special voltage required for programming) on some chips which Apple sometimes tied to an address pin. I'm not sure why they would connect Vpp if they tied WE high though.

I have 12 new Atmel AT29C020 ROMs coming, so whenever I can source some cheap DIP32 to PLCC32 adapters and get them from china, I'll give them a go onboard, with A19 patched in via wires. It'll be a cool experiment! The goal is a sampled startup sound from a Mac IIci.

Click to expand...

If you find you need some 040 chips (4 Megabit) let me know. I think I've got a bunch of AT49F040 in the attic. I have some projects in mind for them, but I can certainly spare a handful for interesting ROM module experiments.