ExROM

The generic designation ExROM refers to cartridge boards made by Nintendo that use the Nintendo MMC5 mapper.

The following ExROM boards are known to exist:

Board	PRG ROM	PRG RAM	CHR
EKROM	128,256,512,1024 KB	8 KB	128,256,512,1024 KB ROM
ELROM	128,256,512,1024 KB		128,256,512,1024 KB ROM
ETROM	128,256,512,1024 KB	16 KB (2x 8KB)	128,256,512,1024 KB ROM
EWROM	128,256,512,1024 KB	32 KB	128,256,512,1024 KB ROM

Solder Pad Config

• MMC5 in 'CL mode' (default) : 'CL3', 'CL4', 'CL5' and 'CL6' connected, 'SL3', 'SL4', 'SL5' and 'SL6' disconnected.
• MMC5 in 'SL mode' : 'CL3', 'CL4', 'CL5' and 'CL6' disconnected, 'SL3', 'SL4', 'SL5' and 'SL6' connected.

• RAM chip with data retention (default) : 'CL2' connected, 'SL2' disconnected, with Battery, D1, R5, R6, R8 present.
• RAM chip without data retention : 'CL2' disconnected, 'SL2' connected, with Battery, D1, R5 and R6 removed.

• Second RAM chip (if present) with data retention : 'CL1' disconnected, with battery, D1 and R7, R8 present.
• Second RAM chip (if present) without data retention (default) : 'CL1' connected, 'SL1' disconnected, R7 removed.

• Sound circuitry used : R1, R2, R4, R9, C2, C3 present (NES-ExROM). An American or European NES must be modified to output cartridge audio, even if the audio circuitry is implemented. R1, R2, R3, R4, C2, C3, and C4 present (HVC-ExROM).
• Sound circuitry unused : R1, R2, R4, R9, C2, and C3 not present (NES-ExROM). No Famicom cartridges ever disabled the MMC5 audio.

NES-ExROM boards entirely omitted R3 and C4, and added R9 (nominally 10kΩ) between R4 and the output to the cartridge edge. The silkscreened values on NES-EKROM and NES-EWROM, and Famicom games that actually used the expansion audio, replace R1 with 6.8kΩ. It is not known what signal comes from pin 3, but it seems likely to be the pulse waves. MMC5 pins 1 and 100 are probably an inverter used as an amplifier.

• NES-ETROM additionally provides a solder jumper pair 'CL15' and 'SL15'. It is not known what this does.