Acclaim 55741


Tech Specs:

Max. 256K PRG ROM.
Max. 256K CHR RAM
Weird MMC3 clone


Acclaim was trying to save money apparently, so they had their own version of the MMC3 made. It seems to work the same as the real MMC3. The chip is marked "MC-ACC" / (C) 1991 ACCLAIM" and is in a 40 pin DIP package. The 74HC08 quad AND gate is connected up as a digital pulse filter. Three of the gates are simply chained together, and the output of the chain feeds into the final AND, along with the input signal. The input signal is PPU A12, and the output of this mess runs to the MC-ACC chip. Apparently, some very fine pulses were screwing their counter up. Nintendo had this problem too, but opted for a simple capacitor from PPU A12 to ground.

See the MMC3 documentation for info on the mapper.

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