INES Mapper 108

NES 2.0 Mapper 108 denotes at least four different PCBs used for FDS-to-cartridge conversions. All have nametable mirroring hard-wired.

Used by Whirlwind Manu’s first release of Taito’s Bubble Bobble (LH31), and is a modified version of Kaiser’s cartridge conversion, originally for INES Mapper 142.

Banks:

• CPU $6000-$7FFF: Switchable 8 KiB bank
• CPU $8000-$FFFF: Fixed to last 32 KiB of PRG-ROM
• PPU $0000-$1FFF: Unbanked 8 KiB CHR-RAM

Registers:

• CPU $F000-$FFFF: Select 8 KiB PRG-ROM bank at CPU $6000-$7FFF. The game retains writes outside this address range, which must be ignored for the game not to crash.

Used by Whirlwind Manu’s later release of Taito’s Bubble Bobble (LH31) that replaces CHR-RAM with CHR-ROM. UNIF board name is UNL-BB.

Banks:

• CPU $6000-$7FFF: Switchable 8 KiB bank
• CPU $8000-$FFFF: Fixed to last 32 KiB of PRG-ROM
• PPU $0000-$1FFF: Switchable 8 KiB CHR-ROM bank

Registers:

• CPU $E000-$FFFF: Select 8 KiB PRG-ROM bank at CPU $6000-$7FFF *and* 8 KiB CHR-ROM bank at PPU $0000-$1FFF. The game retains writes outside this address range, which must be ignored for the game not to crash.

Submapper 1 but with the PRG-ROM switch responding in the full CPU $8000-$FFFF address range, which is required for both games to function:

• Falsion (LH54)
• Meikyuu Jiin Dababa (LH28)

Banks:

• CPU $6000-$7FFF: Switchable 8 KiB bank
• CPU $8000-$FFFF: Fixed to last 32 KiB of PRG-ROM
• PPU $0000-$1FFF: Unbanked 8 KiB CHR-RAM

Registers:

• CPU $8000-$FFFF: Select 8 KiB PRG-ROM bank at CPU $6000-$7FFF

Like Submapper 2, but with the CHR-ROM switch responding in the full CPU $8000-$FFFF address range, and PRG-ROM banks being fixed. UNIF board name is also UNL-BB.

• Pro Wrestling (LE05)

Banks:

• CPU $6000-$7FFF: 8 KiB bank, fixed to last 8 KiB
• CPU $8000-$FFFF: Fixed to last 32 KiB of PRG-ROM
• PPU $0000-$1FFF: Switchable 8 KiB CHR-ROM bank

Registers:

• CPU $8000-$FFFF: Select 8 KiB CHR-ROM bank at PPU $0000-$1FFF

FCEUX and Mesen manage to emulate all four PCBs without disambiguation by heuristically considering the addresses that all games write to:

if((addr & 0x9000) == 0x8000 || addr >= 0xF000){
    //A version of Bubble Bobble expects writes to $F000+ to switch the PRG banks
    _prgReg = _chrReg = value;
} else {
    //For ProWres
    _chrReg = value & 0x01;
}

To disambiguate the four different PCBs in advance:

• CHR-RAM -> Submappers 1 or 3
  • Horizontal Mirroring -> Submapper 1, otherwise 3
• CHR-ROM -> Submappers 2 or 4
  • More than 16 KiB of CHR-ROM -> Submapper 2, otherwise 4

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