NES 2.0 Mapper 431

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NES 2.0 Mapper 431 denotes the Realtec GN-91B, used by a multicart consisting of two UNROM games.

Outer Bank Register ($8000-$BFFF)

Mask: $C000

D~7654 3210 (bus conflicts)
  ---------
  ..P. ...M
    |     +- 0: Vertical mirroring
    |        1: Horizontal mirroring
    +--- PRG A17

Inner Bank Register ($C000-$FFFF)

Mask: $C000

D~7654 3210 (bus conflicts)
  ---------
  .... .PPP
        +++- PRG A16..A14 if CPU A14=0
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