NES 2.0 Mapper 303

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NES 2.0 Mapper 303 is used for Kaiser's ROM cartridge conversion of the Famicom Disk System game アルマナの奇跡 (Almana no Kiseki). Its UNIF board name is UNL-KS7017.


  • CPU $6000-$7FFF: 8 KiB unbanked PRG-RAM
  • CPU $8000-$BFFF: 16 KiB switchable PRG-ROM bank
  • CPU $C000-$FFFF: 16 KiB fixed PRG-ROM bank #2
  • PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM


PRG Bank Latch ($4A00-$4AFF)

Mask: probably $FF00

A~FEDC BA98 7654 3210
  0100 1010 .P.. PP..
             +---++-- Select 16 KiB PRG-ROM bank at CPU $8000-$BFFF

The new PRG bank number is not applied until register $5100 is written to.

PRG Bank Latch Commit ($5100)

Mask: probably $FF00

Mirroring, IRQ ($4020, $4021, $4025 bit 3: write, $4030 bit 0: read)

Identical to their respective equivalents on the Famicom Disk System.


The conversion retains all writes to the FDS sound channel registers, so an emulator could provide the expansion sound channel even though the original Kaiser cartridge did not.