iNES Mapper 185 is used for games that use the CNROM board with weak copy protection measures.
7 bit 0 ---- ---- ..CC ..CC || || ++---++- Used for CHR copy protection.
These games only have 8k of CHR, and they attempt to disable CHR by writing a specific value to the CHR Reg, then VERIFY that garbage is read back, then they swap back to the actual CHR. If they don't get the expected garbage, they lock up.
Each game has their own value that enables/disables CHR. The correct value may be specified using the submapper field in the NES 2.0 header. If an iNES image's header does not specify a submapper, then a heuristic must be used to allow these games to run. Two heuristics are commonly used by emulators:
When CHR is disabled, the pattern tables are open bus. Theoretically, this should return the LSB of the address read, but real-world behavior varies.
This table has been assembled from nocash and the sources of MESS, Nestopia, and FCEUX; the specific tests were traced from dumps in GoodNES.
bank | PPU addr | test | bank | PPU addr | test | |
---|---|---|---|---|---|---|
Game | Incorrect bank | Must work | ||||
Bird Week | $F0 | $1FF0 | ≠ $0C | $0F | $1FF0 | = $0C |
B-Wings | $00 | $0000 | ≠ $3C | $33 | $0000 | = $3C |
Mighty Bomb Jack (J) | $00 | $0000 | ≠ $00 | $11 | untested | |
Mighty Bomb Jack (U), (E) | $00 | $0001 | ≠ $3C | $11 | untested | |
Sansuu 1 Nen | $20 | $000C | ≠ $BC | $22 | $000C | = $BC |
Sansuu 2 Nen | $20 | $0003 | ≠ $42 | $22 | $0003 | = $42 |
Othello | $20 | $0006 | ≠ $3F | $22 | $0006 | = $3F |
Sansuu 3 Nen | $00 | $0006 | ≠ $34 | $2A | $0006 | = $34 |
Spy vs Spy | $13 | $1F20 | ≠ $55 | $21 | untested | |
Seicross (v2) | $21 | $0700…$0707 | ≠ $20,$60,$70,$70,$70,$40,$08,$38 | $20 | untested |
Categories: INES Mappers, In NesCartDB, Discrete logic mappers, Mappers with bus conflicts, Nintendo licensed mappers, NES 2.0 mappers with submappers