FxROM

The generic designation FxROM refers to cartridge boards made by Nintendo that use the Nintendo MMC4 mapper.

Board Types

The following FxROM boards are known to exist:

Board	PRG ROM	PRG RAM	CHR
FJROM	128 / 256 KB	8 KB	16 / 32 / 64 KB ROM
FKROM	128 / 256 KB	8 KB	128 KB ROM

Overview

• PRG ROM size: up to 256 KB
• PRG ROM bank size: 16 KB
• PRG RAM: 8 KB plus optional battery
• CHR capacity: up to 128 KB ROM
• CHR bank size: 4 KB
• Nametable mirroring: Controlled by mapper
• Subject to bus conflicts: No

Solder Pad config

Battery backup

• PRG RAM with data retention : 'SL' disconnected, D1, D2, R1, R2, R3 present.
• PRG RAM without data retention : 'SL' connected, D1, D2, R1, R2, R3 not present.

On the FKROM board, battery backup appears to be compulsary unless there is a hidden solder pad below the MM1026 chip.

Hardware

The FKROM board uses a Mitsumi MM1026 chip dedicated to safe battery backup. It's the only Nintendo board to use a specific chip dedicated to safe battery backup.

See also

• Nintendo MMC4