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.
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
Categories: GNROM-like mappers, Multicart mappers