TxROM

The generic designation TxROM refers to cartridge boards made by Nintendo that use the Nintendo MMC3 mapper.

The following TxROM boards are known to exist:

Board	PRG ROM	PRG RAM	CHR	Comments
TBROM	64 KiB		16, 32, 64 KiB ROM
TEROM	32 KiB		16, 32, 64 KiB ROM	Supports fixed mirroring
TFROM	128, 256, 512 KiB		16, 32, 64 KiB ROM	Supports fixed mirroring
TGROM	128, 256, 512 KiB		8 KiB RAM/ROM
TKROM	128, 256, 512 KiB	8 KB	128, 256 KiB ROM
TK1ROM	128 KiB	8KiB	128KiB ROM	Uses 7432 for 28-pin CHR ROM
TKSROM	128, 256, 512 KiB	8 KB	128 KiB ROM	Alternate mirroring control
TLROM	128, 256, 512 KiB		128, 256 KiB ROM
TL1ROM	128 KiB		128 KiB	Uses 7432 for 28-pin CHR ROM
TL2ROM			Nonstandard pinout
TLSROM	128, 256, 512 KiB		128 KiB ROM	Alternate mirroring control
TNROM	128, 256, 512 KiB	8 KB	8 KiB RAM/ROM	Famicom only
TQROM	128 KiB		16, 32, 64 KiB ROM + 8 KiB RAM
TR1ROM	128, 256, 512 KiB		64 KiB ROM + 4 KiB VRAM (4-screen Mirroring)	NES only
TSROM	128, 256, 512 KiB	8 KiB (no battery)	128, 256 KB ROM
TVROM	64 KiB		16, 32, 64 KiB ROM + 4 KiB VRAM (4-screen Mirroring)	NES only

Solder pad config

Namco 108 backwards compatibility mode (TEROM and TFROM)

Normal mode

'CL1' connected, 'CL2' connected, 'H' disconnected, 'V' disconnected.

DxROM backward compatibility mode with horizontal mirroring

'CL1' disconnected, 'CL2' disconnected, 'H' disconnected, 'V' connected (for vertical arrangement)

DxROM backward compatibility mode with vertical mirroring

'CL1' disconnected, 'CL2' disconnected, 'H' connected, 'V' disconnected (for horizontal arrangement)

Connecting 'CL1' enables MMC3-controlled mirroring, while connecting 'CL2' enables IRQs. However, the additional bankswitching modes available by the MMC3 that weren't available with the 109 chip used on DEROM boards are still present and activated by bits 7-6 of port $8000.

Battery retention (TNROM, TKROM, and TKSROM)

• PRG RAM retaining data: 'SL' disconnected, Battery, D1, D2, R1 R2 and R3 present.
• PRG RAM not retaining data: 'SL' connected, leave slots for Battery, D1, D2, R1, R2 and R3 free.

Various notes

Boards with 4-screen mirroring uses a 8 KB SRAM chip, but only 4 KB is actually used. The 2 KB VRAM inside of the console is always disabled, and the CIRAM A10 pin of the MMC3 doesn't go to anything.

TLSROM and TKSROM boards have different mirroring control than other MMC3 boards. The mirroring is controlled directly by MMC3's CHR A17 line, and MMC3's CIRAM A10 pin doesn't go to anything. Due to their incompatibility with other MMC3 boards on a software viewpoint, they are assigned to INES Mapper 118 instead of mapper 4.

TQROM board has both CHR ROM and RAM. Bit 6 of the bank number, which appears on MMC3's CHR A16 line, controls whenever CHR RAM or CHR-ROM is enabled. A 74HC32 chip is used to combine this with other chip enable signals for the CHR-ROM and the CHR-RAM chips. Due to this incompatibility with the other MMC3 boards on a software viewpoint, this board is assigned to INES Mapper 119 instead of mapper 4.