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

References

• Disch's Mapper Notes