INES Mapper 206
iNES Mapper 206 is a stripped-down version of MMC3 used by Tengen and Namco. Chips used include "Tengen MIMIC-1" and "Namcot 118", and the boards made by Nintendo of America that used this mapper are NES-DxROM. Many ROMS using this mapper are incorrectly listed as using MMC3, but will usually work if emulated with MMC3, and the mirroring is correct, as if they were on a TEROM or TFROM board.
Compared to MMC3:
- There are no IRQs
- There is no WRAM support
- PRG always has the last two 8KiB banks fixed to the end.
- CHR always gives the left pattern table (0000-0FFF) the two 2KiB banks, and the right pattern table (1000-1FFF) the four 1KiB banks.
- Mirroring is hardwired, one game uses 4-screen mirroring (Gauntlet).
- CHR size limit is 64KiB, PRG size limit is 128KiB.
- The two registers are repeated across the entire address space from $8000-$FFFF, not just $8000-$9FFF
Registers:
- $8000: 00000xxx - Select which internal register gets written by $8001
- $8001: 00xxxxxx - Value written to the internal register. PRG registers use only 4 bits.
Internal registers:
- 0, 1: 2k CHR banks at 0000, 0800. Least significant bit is ignored.
- 2, 3, 4, 5: 1k CHR banks at 1000, 1400, 1800, 1C00.
- 6, 7: 8k PRG banks at 8000, A000.
Variants
Mapper 76 increases CHR to 128KiB by inflating the 1KiB CHR banks to 2KiB and making the originally-2KiB banks inaccessible.
Mappers 88 and 154 increase CHR to 128KiB by connecting PPU's A12 line to the CHR ROM's A16 line, making tiles in $0000 and $1000 come from disjoint sections of ROM.
Mapper 154 additionally adds mapper-controlled one-screen mirroring.
Mapper 95 uses the MSB to control mirroring by connecting CHR A15 to CIRAM A10, much as CHR A17 controls CIRAM A10 in TxSROM.
References
- FCEUX source code
