Midway Multigame

There are 8 major parts to my Midway MultiGame:

• CPU ROM switcher- I use a 27C010 that can hold up to 8 game images, and a 74LS00 for address decoding. I wired everything up to accommodate a 27C020, so I can double the number of games easily.
• Graphics ROM switcher- I use two 27C512s that can hold up to 16 game graphics, and a 74LS00 for address decoding. There's also provision for supporting extended graphics images for Moon Cresta and Pisces.
• Color PROM switcher- I use a 27C64 that can hold up to 256(!) game palettes. Super overkill, but the '64 is cheap, plentiful and easy to work with.
• DIP switch switcher- I use a 27C64 that can hold up to 128 game settings.
• Moon Cresta Hack- a 74LS157 switches some address decoding.
• Scramble Hack- another 74LS157 moves some more memory addresses around, and two 2114 RAM chips have to be piggybacked onto the existing RAM to double its size.
• Obviously, the control panel has to be modified to support some of the games- a 4-way joystick must be substituted for War of the Bugs and Scramble, and Scramble also needs a 'bomb' button.
• Lastly, you need a way to switch between the games. I use a simple rotary switch which is encoded to provide the game select address lines.