Looking through my regular SRAM chips, most have a standby mode with just a few micro amps of current draw and function down to 2 volts. So, a perfect match for one of these and a coin cell. That makes programming from scratch easy, and one can iterate without a ROM programmer. Once a subroutine is verified, it can be transferred to an EEPROM. Then there is no fussing with paged erasure, not that erasure is a big deal. It just requires the subroutine and a 12 volt source.
Anyways, the battery backed SRAM on the board is the plan for tomorrow. I might have expanded the real estate a bit today, and built a custom breadboard for the 68k Hershey bar. I don't know if I will mess with the 68k stuff as all chips I have are NMOS, and I think that means they cannot single step through code. Reading up on the Z80, that thing is really really nice compared to the 6502.
Nice. I remember there used to be some machines with battery backed RAM way back. Like canon x-07 iirc.