TxROM

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

Board Types

The following TxROM boards are known to exist:

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