NES 2.0 Mapper 364 is used for an early MMC3-based multicart PCB (JY830832C) from J.Y. Company, preceding the J.Y. Company ASIC:
Mask: unknown D~7654 3210 --------- .PSC .... ||+------ CHR A18 |+------- PRG/CHR A17 mode | 0: Preserve MMC3's PRG/CHR A17 | 1: Force PRG/CHR A17 to 0 +-------- PRG A18
This register is accessible regardless of whether WRAM is enabled in the MMC3 clone's A001 register. It may be possible that there is another bit, unused on the only discovered cartridge using this mapper, that selects the bit value which PRG/CHR A17 is forced to when S=1.
Mask: $E001 See MMC3.
NES 2.0 Mapper 361 describes a simpler variant with a fixed outer bank size.
Categories: MMC3-like mappers, Mappers with scanline IRQs, Multicart mappers