I've posted this up on UKVAC as the board has evolved, but here's a bit of a summary of a single ROM/RAM board I've made for a number of Z80-based games.
At the end of last year I was repairing a load of Galaxian boards, some original, some boots, and found a lot of problems seem to be with the ROM daughterboard (which often goes missing) or the program RAM, so I wanted to design something to make troubleshooting a bit easier.
Buying the already-available single ROM boards for a number of games I own would work out pretty expensive, so I spent some time in January designing my own single ROM/RAM daughterboard that plugs into the Z80 socket and replaces the old ROM board and RAM (RAM is optional). You just need to burn whatever version of Galaxian or clone onto a single chip, choose whether you want to use separate RAM or not and install it if you do, then remove the Z80 and plug it into the daughterboard. Once this was working, it was time to extend to other games.
So rather than it just being dedicated to Galaxian, I tried to make the hardware as generic as possible. The memory addressing for the ROM and RAM is handled by a GAL, and I fed multiple memory address lines plus various control signals into the GAL, so the board isn't restricted to just Galaxian, but other Z80-based games, you just need to reprogram the GAL.
It's so far been tested working with the following games:-
Galaxian (Namco, Midway and bootlegs)
Amidar
Turtles
Pacman (ROM only as the memory addressing is a bit "odd")
Scramble (plus other games on Scramble hardware)
Using a single board does away with the multiple ageing IC sockets that lose their grip over the years, and also reduces power consumption a bit as it uses just one ROM and not the multiple ROMs originally in place.
The final thing is for anyone who does home-brew game coding, or hacking games. Burning a single ROM is a load easier than having to burn multiple ones. Also the RAM on the board can be replaced with a Dallas DS1220 NVRAM module (apart from Pacman), so the home-brew coders can write their own high score save routine.
I plan to get this working with more games as time goes on, and also maybe refresh my old Z80 programming skills...
