NES 2.0 Mapper 558

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NES 2.0 Mapper 558 denotes the 燕城 (Yànchéng) YC-03-09 circuit board, used for the following games:

  • 口袋精靈: 水晶 (Pokémon: Crystal Edition)
  • 大話三國 (Dàhuà Sānguó)

A compatible circuit board with an unknown PCB code is used for the original editions of a few games from 外星 (Wàixīng):

  • Pet Family - 宠物大家族: 部落纷争 (ES-1081)
  • Pet Evolve - 宠物进化史 (ES-1085)
  • 口袋妖怪꞉ 鑽石版 (Pokémon: Diamond Edition, ES-1090)
  • 口袋精靈: 紅 and its title screen hack 宠物: 红 (Pokémon: Red Edition, ES-1088)
  • 数码暴龙 4: 水晶版 and its title screen hack 数码宝贝 (Digimon 4: Crystal Edition)
  • 盟军敢死队 - Commandos

The Yànchéng games save the game state to a 93C66 512-byte serial EEPROM, while the Wàixīng games save to 8 KiB battery-backed WRAM. The NES 2.0 Header's PRG-NVRAM field distinguishes between the two board variants.


  • CPU $6000-$7FFF: up to 8 KiB unbanked PRG-RAM, can be battery-backed
  • CPU $8000-$FFFF: 32 KiB switchable PRG-ROM bank
  • PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM bank
  • Nametable mirroring: hard-wired


All registers are initialized to $00 on reset.

PRG-ROM Bank Low ($5000, write)

Mask: $FF00

D~7654 3210
  .... PPPP
       ++++- PRG A18..A15
  • Note that if $5300.0 is 0, the two lowest bits are swapped during writing.

PRG-ROM Bank High ($5100, write)

Mask: $FB00

D~7654 3210
  .... ..PP
         ++- PRG A20..A19
  • Note that if $5300.0 is 0, the two lowest bits are swapped during writing.

Microwire Interface ($5200, write)

Mask: $FF00

D~7654 3210
  .... .SDC
        ||+- 93C66 EEPROM CLK ($5300.0=0)/DAT ($5300.0=1) output
        |+-- 93C66 EEPROM DAT ($5300.0=0)/CLK ($5300.0=1) output
        +--- 93C66 EEPROM CS output

Mode ($5300, write)

Mask: $FF00

D~7654 3210
  .... .AB.
        |+-  0: Swap D0,D1 on all register writes to $5000-$5200.
        |    1: Leave D0,D1 unmodified on register writes to $5000-$5200.
        +--- 0: PRG A15/A16=1
             1: PRG A15/A16 from $5000
  • Writes to this register are not subject to D0/D1 bit-swapping, i.e. the register is not affected by its own bit 0.
  • Because this register is initialized to $00 on reset, thus clearing bit 2 which causes PRG A15/A16 to be held high, the game will boot in 32 KiB PRG-ROM bank #3.
  • Changing the value of $5300.0 without writing to $5000-$5200 afterwards does not change the latched bits.

Microwire Interface ($5500, read)

Mask: $FF00

D~7654 3210
  .... .A..
        +--- 93C66 EEPROM DAT input

Unlike INES Mapper 164, the EEPROM input is not inverted.


  • CPU D0 and D1 are connected in reverse to the mapper blob compared to other circuit boards using this ASIC. This means that setting $5300.0 to 0, not to 1, will effectively swap PRG A15/A16 and PRG A19/A20. Cartridges using this mapper must be dumped with $5300=$07 during dumping to obtain a readout that matches that of a desoldered ROM chip.
  • The Wàixīng games using this mapper were previously set to 162/163 or 164, resulting in incompatibility either because of the different address of the PRG-ROM Bank High register (mapper 162/163) or the different startup bank (164).

See also

  • INES Mapper 162/163 swap the effective meaning of registers $5100 and $5200, the meaning of the D0/D1 bit swap, and use the microwire interface only for protection purposes.
  • INES Mapper 164 is an earlier implementation without D0/D1 swapping, optional UNROM-like bankswitching, and a 1 bpp CHR mode.
  • PCB images and analysis