NES 2.0 Mapper 321

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NES 2.0 Mapper 321 denotes the 820310 MMC3-based multicart circuit board, UNIF MAPR BMC-820310-C. It is basically NES 2.0 Mapper 287 looking at differently-ordered address bits.

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

A~[011. .... ..PP MB..], A001.7=1, A001.6=0
               || |+---- PRG/CHR A17
               || +----- 0=PRG A16..A13 from MMC3
               ||        1=PRG A16..A15 from PP,
               ||          PRG A14..A13=CPU A14..A13
               ||          (NROM-256-like PRG banking)
               ++------- PRG A16..A15 is M=1