Well, the first problem is that I failed to verify that the game writes to the MMC3 PRG RAM protection register first. It doesn't.
So you'll need to add a 74'20 / '21 / '138 or something to decode that memory region :/ ( AND4/NAND4(A13,A14,M2,/ROMSEL)
Ice Man wrote:
74'139
Even though I screwed up the above, it's possible you got pins 1 and 3 backwards. One of the MMC3 outputs is supposed to be a positive enable, the other a negative enable, and only one permutation would work.
In any case, you may as well redo it with the AND4/NAND4 output, CPUA0, and R/W.
Quote:
Can I leave A18 PRG unconnected? Since 27c040 have it. Or connect it to PRG A18 to MMC3?
You should tie it to something, inputs shouldn't be left floating.
If you've doubled up the game's original 256 KiB to fill the 512 KiB ROM, it shouldn't matter what you tie it to, just that it not be floating when the CPU's trying to get data out of the ROM.