NES 2.0 Mapper 271

NES 2.0 Mapper 271 is used for the TXC 4-in-1 multicart (MGC-026). It's basically an oversize GNROM with one of the PRG bits also serving as a mirroring control. Its UNIF board name is BMC-22026.

Data latch

Mask: $8000

Bit 7654 3210
    ---------
    ..PP CCCC
      || ++++- Select 8 KiB CHR-ROM bank at PPU $0000-$1FFF
      ++------ Select 32 KiB PRG-ROM bank at CPU $8000-$FFFF
      +------- Select nametable mirroring
               0: Horizontal
               1: Vertical