Nintendo MMC4

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Nintendo MMC4 is an ASIC mapper, used on the FxROM board set. The iNES format assigns mapper 10 to these boards. The chip first appeared in August 1987.

Contents

[edit] Overview

  • PRG ROM size: 256 KB
  • PRG ROM bank size: 16 KB
  • PRG RAM: 8 KB + battery
  • CHR capacity: 128 KB
  • CHR bank size: 4 KB
  • Nametable mirroring: Vertical or horizontal, controlled by program
  • Subject to bus conflicts: No

[edit] Banks

  • CPU $6000-$7FFF: 8 KB fixed PRG RAM bank
  • CPU $8000-$BFFF: 16 KB switchable PRG ROM bank
  • CPU $C000-$FFFF: 16 KB PRG ROM bank, fixed to the last bank
  • PPU $0000-$0FFF: Two 4 KB switchable CHR ROM banks
  • PPU $1000-$1FFF: Two 4 KB switchable CHR ROM banks

When the PPU reads from specific tiles in the pattern table during rendering, the MMC4 sets a latch that tells it to use a different 4 KB bank number. This has the effect of setting a different bank for all tiles to the right of a given tile.

  • PPU reads $0FD0 through $0FDF: latch 0 is set to $FD
  • PPU reads $0FE0 through $0FEF: latch 0 is set to $FE
  • PPU reads $1FD0 through $1FDF: latch 1 is set to $FD
  • PPU reads $1FE0 through $1FEF: latch 1 is set to $FE

[edit] Registers

[edit] PRG ROM bank select ($A000-$AFFF) 

7  bit  0
---- ----
xxxx PPPP
     ||||
     ++++- Select 16 KB PRG ROM bank for CPU $8000-$BFFF

[edit] CHR ROM $FD/0000 bank select ($B000-$BFFF) 

7  bit  0
---- ----
xxxC CCCC
   | ||||
   +-++++- Select 4 KB CHR ROM bank for PPU $0000-$0FFF
           used when latch 0 = $FD

[edit] CHR ROM $FE/0000 bank select ($C000-$CFFF) 

7  bit  0
---- ----
xxxC CCCC
   | ||||
   +-++++- Select 4 KB CHR ROM bank for PPU $0000-$0FFF
           used when latch 0 = $FE

[edit] CHR ROM $FD/1000 bank select ($D000-$DFFF) 

7  bit  0
---- ----
xxxC CCCC
   | ||||
   +-++++- Select 4 KB CHR ROM bank for PPU $1000-$1FFF
           used when latch 1 = $FD

[edit] CHR ROM $FE/1000 bank select ($E000-$EFFF) 

7  bit  0
---- ----
xxxC CCCC
   | ||||
   +-++++- Select 4 KB CHR ROM bank for PPU $1000-$1FFF
           used when latch 1 = $FE

[edit] Mirroring ($F000-$FFFF) 

7  bit  0
---- ----
xxxx xxxM
        |
        +- Select nametable mirroring (0: vertical; 1: horizontal)

[edit] Hardware

The MMC4 is implemented in a 44-pin TQFP package. Only one revision is known to exist.

[edit] Variants

The Nintendo MMC2, used in PxROM boards, is a similar mapper with 8 KB switchable PRG ROM banks, a 24 KB fixed PRG ROM bank, and no PRG RAM.

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