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
- DIP switch switcher- I use a 27C64 that can hold up to 128 game settings.
- Moon Cresta Hack- a 74LS157 switches some
- 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.
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