NES 2.0 Mapper 270

NES 2.0 Mapper 270 denotes OneBus console multicarts that use the consoles' universal input/output (UIO) register $412C to bankswitch higher-order PRG address lines or several PRG chips, and select CHR-RAM via $4242.

Submapper 0: Combination

Responds to all bank bits of submappers 1-3 at the same time. This is permissible, since the only bit that is used by several submappers has the same function in each of them.

Submapper 1: Game Prince RS-16

Outer PRG Bank ($412C, write)

D~7654 3210
  ---------
  .... ..A.
         +-- PRG/CHR A24

Submapper 2: Family Pocket 638-in-1

Outer PRG Bank ($412C, write)

D~7654 3210
  ---------
  .... ..AB
         |+- PRG/CHR A25
         +-- PRG/CHR A24

Jumper Cartridge Detection ($412C, read)

D~7654 3210
  ---------
  .... B...
       +---- 0: Jumper cartridge not inserted
             1: Jumper cartridge inserted

CHR-RAM enable ($4242, write)

D~7654 3210
  ---------
  .... ...C
          +- 0: Use normal OneBus CHR banking
             1: Use 8 KiB of unbanked CHR-RAM

Submapper 3: Bittboy 300-in-1

Outer PRG Bank ($412C, write)

D~7654 3210
  ---------
  .... .A..
        +--- PRG/CHR A24

Notes

• Any $412C bit can only be read from if the corresponding bit in register $412B (UIO input/output selector) is set to "0" (input).
• Any $412C bit can only be written to if the corresponding bit in register $412B (UIO input/output selector) is set to "1" (output).