NES 2.0 Mapper 512

NES 2.0 Mapper 512 is used for 中國大亨 (Zhōngguó Dàhēng, often incorrectly rendered in Japanese as Chūgoku Taitei), a Chinese board game similar to Game of the Goose by Sachen. It uses an MMC3 clone with both CHR-ROM and at least 4 KiB of CHR-RAM, 4 KiB of additional VRAM, plus 8 KiB of battery-backed WRAM at CPU $6000-&7FFF.

Registers

Mask: $E011

   $8000, $8001, $A000, $A001, $C000, $C001, $E000, $E001: As normal MMC3.

Mask: unknown, but probably $C100

$4100: Set CHR and VRAM mode
        0: CHR-ROM, CIRAM with MMC3-determined mirroring
        1: CHR-ROM, Cartridge VRAM
        2: CHR-RAM, CIRAM with MMC3-determined mirroring
        3: Seemingly identical to 2

Notes

• The game uses four pages of cartridge VRAM for the main game board, plus the two pages of CIRAM for the status bar, for a total of six nametable pages.
• While the fact that cartridge VRAM and CHR-RAM cannot be enabled at the same time might suggest that the same 4 KiB of RAM are used for both purposes, such is not the case, as the game board is expected to retain its content while Chinese characters are written into CHR-RAM.
• Even as the game uses WRAM at CPU $6000-$7FFF, it fails to enable it by writing $80 to $A001. Apparently, the MMC3 clone does not allow disabling WRAM.