INES Mapper 221

iNES Mapper 221 is used for multicarts using the NTDEC N625092 PCB. They have 8 KiB of unbanked CHR-RAM at PPU $0000-$1FFF. Their UNIF board name is BMC-N625092.

Mode/Outer Bank Register ($8000-$BFFF)

A~FEDC BA98 7654 3210
  -------------------
  10.. ..Bp ...O OOPM
         ||    | |||+- Select nametable mirroring type
         ||    | |||    0: Vertical
         ||    | |||    1: Horizontal
         ||    | ||+-- Select NROM-128/Other PRG-ROM modes
         ||    | ||     0: NROM-128 (Inner Bank selects 16 KiB PRG-ROM bank
         ||    | ||        at CPU $8000-$BFFF mirrored at CPU $C000-$FFFF)
         ||    | ||     1: Other mode (decided by bit 8)
         ||    +-++--- Select 128 KiB Outer PRG-ROM bank (PRG A17-A19)
         |+----------- Select PRG-ROM mode if bit 1=1
         |              0: NROM-128 (Inner Bank SHR 1 selects 32 KiB PRG-ROM
         |                 bank at CPU $8000-$FFFF)
         |              1: UNROM (Inner Bank selects 16 KiB PRG-ROM bank at
         |                 CPU $8000-$BFFF, CPU $C000-$FFFF fixed to Inner Bank #7)
         +------------ Select 1 MiB Outer PRG-ROM bank (PRG A20)

Inner Bank Register ($C000-$FFFF)

A~FEDC BA98 7654 3210
  -------------------
  11.. .... .... CIII
                 |+++- 16/32 KiB (depending on PRG-ROM mode) Inner Bank number
                 +---- Select CHR-RAM write-protection
                        0: Disabled, CHR-RAM write-enabled
                        1: Enabled, CHR-RAM write-protected