INES Mapper 185
iNES Mapper 185 is used for games that use the CNROM board with weak copy protection measures.
Example Games:
- Spy Vs. Spy (J)
- Mighty Bomb Jack (J)
Overview
- PRG ROM size: 16 KiB or 32 KiB
- PRG ROM bank size: Not bankswitched
- PRG RAM: None
- CHR capacity: 8 KiB ROM (copy protected)
- Nametable mirroring: Solder pads select vertical or horizontal mirroring
- Subject to bus conflicts: Yes
Banks
- PPU $0000-$1FFF: 8 KB switchable CHR ROM bank
Registers
Bank select ($8000-$FFFF)
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.
Perhaps this was some sort of copy protection?
Each game has their own value that enables/disables CHR. Rather than failing to attempt to list all the exact values used here (I don't know what all of them are), I can provide some logic:
if C AND $0F is nonzero, and if C does not equal $13: CHR is enabled otherwise CHR is disabled
When CHR is disabled, the pattern tables are open bus. Theoretically, this should return the LSB of the address read, but real-world behavior may vary.
This table has been assembled from nocash and the sources of MESS, Nestopia, and FCEUX.
| if this value is written | ||
|---|---|---|
| Game | Must work | Mustn't work |
| Bird Week | 0x0F | 0xF0 |
| B-Wings | 0x33 | 0x00 |
| Mighty Bomb Jack | 0x11 | 0x00 |
| Sansuu 1 Nen, Sansuu 2 Nen, and Othello | 0x22 | 0x20 |
| Sansuu 3 Nen | 0xFF | 0x00 |
| Spy vs Spy | 0x21 | 0x13 |
| Seicross (v2) | 0x20 | 0x21 |
