Due to the lack of NROM carts and the problem of the 28 eight-pin mask ROM's, i decided to rewrite MMC1 (SLROM) for the NROM dev cart (two 32pin DIP socket).
Initially I was going to completely disconnect MMC1 that connections are 100% identical to the original NROM, but I noticed that the launch NROM'a directly on the card works, only problems with the switch mirroring (which MMC1 is controlled by the controller automatically).
I cut only the connections that MMC1 controls mirroring and left them as is the original NROM. Several tested NROM now works perfectly (all NROM-256, 32+8kb)
I wonder now why does it work? PRG ROM A14 is controlled by MMC1, the same CHR ROM A12. Is MMC1 default does not switch banks (If there is no code in PRG ROM forcing the controller to switch the bank) and therefore NROM works without problems?
Initially I was going to completely disconnect MMC1 that connections are 100% identical to the original NROM, but I noticed that the launch NROM'a directly on the card works, only problems with the switch mirroring (which MMC1 is controlled by the controller automatically).
I cut only the connections that MMC1 controls mirroring and left them as is the original NROM. Several tested NROM now works perfectly (all NROM-256, 32+8kb)
I wonder now why does it work? PRG ROM A14 is controlled by MMC1, the same CHR ROM A12. Is MMC1 default does not switch banks (If there is no code in PRG ROM forcing the controller to switch the bank) and therefore NROM works without problems?