iNES Mapper 187 is used for the 卡聖 (Kǎshèng) A98402 and similar boards, an MMC3-clone-bearing board with an NROM-like PRG-ROM register that can override the MMC3 clone's PRG-ROM bank, and supports 512 KiB of CHR-ROM. Used by:
Mask: $F001
D~7654 3210
---------
M.NB BBb.
| |+-+++-- Select 16 KiB PRG-ROM bank at CPU
| | $8000-$BFFF and $C000-$FFFF
| +------- 0: Do not replace bit 1 (NROM-128)
| 1: Replace bit 1 with CPU A14 (NROM-256)
+--------- 0: Use PRG bank from MMC3; ignore $5000 bits 1-4/5
1: Ignore PRG bank from MMC3; apply $5000 bits 1-4/5
Mask: Unknown
The actual values that are returned are unknown; The King of Fighters '96 reads from here and only expects bit 7 of the value being returned to be set.
Mask: $E001
D~7654 3210
---------
M... ....
+--------- Select CHR A18 Mode
0: CHR A18=inverted PPU A12
1: CHR A18=PPU A12
Basically, either sprites or background tiles will come from the second 256 KiB of CHR-ROM. Note that setting bit 7 will still also activate the MMC3 clone's CHR A12 inversion.
Mask: $E001, see MMC3.
Categories: Mappers using $4020-$5FFF, Mappers with scanline IRQs, MMC3-like mappers