NES 2.0 Mapper 430

NES 2.0 Mapper 430 denotes the MMC3-based 831031C/T-308 multicart circuit board.

Outer Bank Register ($6000-$7FFF, write)

Mask: $E000

A~FEDC BA98 7654 3210
  -------------------
  011. .... .... MNBb
                 ||++- PRG/CHR A18..A17
                 |+--- 0: CHR A17=MMC3 CHR A17 (256 KiB inner CHR bank)
                 |     1: CHR A17=b (128 KiB inner CHR bank)
                 +---- 0: Normal MMC3 PRG banking mode
                       1: GNROM-like PRG banking mode

The MMC3 can only select 128 KiB of PRG-ROM; the b bit always selects PRG A17.

GNROM mode means that the MMC3’s CPU A14 input is held low, so MMC3 registers 6 and 7 apply to both $8000/$A000 and $C000/$E000,

As it uses the MMC3 clones’s WRAM interface, writing to the outer bank register requires enabling and not write-protecting WRAM in the MMC’s $A001 register.

MMC3-compatible registers ($8000-$FFFF)

Mask: $E001

See MMC3.

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