NES 2.0 Mapper 542

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NES 2.0 Mapper 542 denotes the unmarked PCB used in 毛泽东诞辰: 一百周年纪念 1893-1993 (Máozédōng Dànchén꞉ Yībǎi Zhōunián Jìniàn 1893-1993, Mao Zedong's Birthday: 100th Anniversary 1893-1993). The game is a modification of 英雄傳 - World Hero, which is assigned either to mapper 23.1 or to 27.

It uses the same VRC4 clone (A0/A1), increases the PRG-ROM size from the original's 128 KiB to 256 KiB, keeps the 512 KiB of CHR-ROM, additionally maps another fixed part of PRG-ROM to $6000-$7FFF, and most interestingly, can map CIRAM into CHR address space.

Banks

  • CPU $6000-$7FFF: 8 KiB PRG-ROM bank, fixed to bank $0F
  • CPU $8000-$9FFF (or $C000-$DFFF): 8 KiB switchable PRG ROM bank (like VRC4)
  • CPU $A000-$BFFF: 8 KiB switchable PRG ROM bank (like VRC4)
  • CPU $C000-$DFFF (or $8000-$9FFF): 8 KiB PRG ROM bank, fixed to the second-last bank (like VRC4)
  • CPU $E000-$FFFF: 8 KiB PRG ROM bank, fixed to the last bank (like VRC4, $1F in this case)
  • PPU $0000-$03FF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $0400-$07FF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $0800-$0BFF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $0C00-$0FFF: 1 KiB switchable CHR bank (like VRC4) or 1 KiB CIRAM bank #1
  • PPU $1000-$13FF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $1400-$17FF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $1800-$1BFF: 1 KiB switchable CHR bank (like VRC4)
  • PPU $1C00-$1FFF: 1 KiB switchable CHR bank (like VRC4)

Registers

Enable CIRAM mapping to PPU $0C00-$0FFF ($D800, write)

Mask: $F800

Once address $D800 is written to, PPU $0C00-$0FFF is mapped to CIRAM bank 1 instead, ignoring the respective VRC4 register. The game uses this CIRAM as pseudo-CHR-RAM to animate the screen showing the next opponent.

Disable CIRAM mapping to PPU $0C00-$0FFF ($E800, write)

Mask: $F800

Once address $E800 is written to, PPU $0C00-$0FFF is no longer mapped to CIRAM bank 1, and the respective VRC4 register applies again.

VRC4 registers ($8000-$FFFF)

Same as on VRC4.