NES 2.0 Mapper 339

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NES 2.0 mapper 339 is used for a 21-in-1 multicart. Its UNIF board name is BMC-K-3006.

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

Mask: $E000

A~FEDC BA98 7654 3210
  0110 .... ..PO OIIi
              || |+++- Select 16 KiB inner PRG-ROM bank at CPU $8000-$BFFF and
              || |     $C000-$FFFF (NROM-128) if P=0.
              || |     If P=0 and II=6, i is replaced with CPU A14 (NROM-256).
              |+-+---- Select 128 KiB outer PRG-ROM and CHR-ROM bank
              +------- Select PRG banking mode
                        0: NROM, use OO and IIi bits
                        1: MMC3, use only OO bits

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

Mask: $E001

See MMC3.