NES 2.0 Mapper 558

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.

Banks

• 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

Registers

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 1, the two lowest bits are swapped during writing.
• Changing the value of $5300.0 without writing to $5000 afterwards does not change the latched bits.

PRG-ROM Bank High ($5100, write)

Mask: $FB00

D~7654 3210
  ---------
  .... ..PP
         ++- PRG A20..A19

• Note that if $5300.0 is 1, the two lowest bits are swapped during writing.
• Games with 1 MiB PRG-ROM that set $5300.0=1 still use bit 0 to denote PRG A19; they must connect both ASIC PRG A19 and A20 outputs to the ROM chip's A19 pin.

Microwire Interface ($5200, write)

Mask: $FF00

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

Note that if $5300.0 is 1, there are two effects on this register:

• the two lowest bits are swapped during writing before being latched;
• the two latched bits are swapped before being output as long as $5300.0 remains 1.

These two effects counteract each other, so that register $5200 effectively operates identically regardless of the $5300.0 value. When writing to $5300 and changing its bit 0 without writing to $5200 afterwards, ...

• the latched values of B and C remain as when they were written, but
• the choice of which latched bit to be output to the DAT and CLK pins changes;

or in other words, the DAT and CLK pins swap their values until $5200 is written to again.

Mode ($5300, write)

Mask: $FF00

D~7654 3210
  ---------
  .... .A?B
        | +- 0: Leave D0,D1 unmodified on register writes to $5000-$5200.
        |    1: Swap D0,D1 on all 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.

Microwire Interface ($5500, read)

Mask: $FF00

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

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

Notes

• Setting $5300.0=1 will effectively swap PRG A15/A16 and PRG A19/A20. Cartridges using this mapper must be dumped with $5300=$04 during dumping, even if the games run with $5300=$07. Otherwise, PRG A15/A16 and PRG A19/A20 would be swapped both during dumping and emulation, negating the effect; such images will therefore not work with an accurate emulation of this mapper.
• 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 meaning of registers $5100 and $5200, 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.