User talk:Zzo38/Mapper C
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Hardware required
- Two NAND gates making an SR latch using PPU A11 and A10, producing CHR A12 or A13
- One NAND gate decoding PPU A12 & A13 to make PRG A15
- One NAND gate decoding two of the three of (/ROMSEL, A12, M2) going to 6264 RAM -CE
- The last of those three signals goes to 6264 +CE
A few complicating factors:
- the PPU always fetches 34 tiles per scanline, so even with a scroll of (256,240) it will fetch from the nametable at $2800 before it fetches the sprites.
- At this precise moment, Visual2C02 is simulating the unused sprite fetches as coming from tile 0, not tile $FF as documented elsewhere.