NES 2.0 Mapper 541

NES 2.0 Mapper 541 denotes the Korean 리틀컴 (LittleCom) 160-in-1 multicart.

Address latch ($C000-$FFFF, write)

Mask: $C000

A~FEDC BA98 7654 3210
  -------------------
  11.. .... PPPP PpBM
            |||| |||+- Nametable mirroring
            |||| |||    0: Horizontal
            |||| |||    1: Vertical
            |||| ||+-- Set PRG A14 behavior
            |||| ||     0: PRG A14=CPU A14 (NROM-256)
            |||| ||     1: PRG A14=p (NROM-128)
            ++++-++--- Set 16 KiB PRG-ROM bank (PRG A14..A19)
                       at CPU $8000-$BFFF/$C000-$FFFF,
                       p replaced with CPU A14 if B=0

Notes

CHR pattern data is stored in 8 KiB of unbanked CHR-RAM.
Some games write to the unmapped CPU address range $8000-$BFFF. These writes have no effect.
The mirroring bit works in the opposite way compared to most mappers.

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