NES 2.0 Mapper 534

NES 2.0 Mapper 534 is used for 2-in-1 数独/五子棋 (Sudoku/Gomoku, NJ064) cartridge from Shenzhen Nanjing Technology (深圳市南晶). It uses an MMC3 clone with additional circuitry for changing the MMC3's two fixed banks. Pattern tables are stored in 8 KiB of unbanked CHR-RAM.

MMC3-compatible registers ($8000-$FFFF, write)

These registers function identically to a normal MMC3, except in NROM mode.

NROM Register ($6000, write)

Mask: probably $E003

D~7654 3210
  ---------
  .N.. ...P
   |      +- PRG A14 mode if N=1
   |          0: PRG-ROM A14=CPU A14 (NROM-256)
   |          1: PRG-ROM A14=1 (NROM-128)
   +-------- NROM mode
              0: disabled: PRG-ROM connected normally to MMC3
              1: enabled: MMC3 CPU A14 input held low;
                 PRG-ROM A14 subject to "p" bit

If N=1, the two MMC3 bank registers 6 and 7 specify PRG-ROM's A15-A17 (i.e. the 32 KiB bank) for both CPU $8000-$BFFF and $C000-$FFFF, and the 16 KiB bank in that range is determined by the P bit: If P=0, the 16 KiB bank bit is substituted with CPU address bit 14 to form one 32 KiB bank similar to NROM-256. If P=1, the 16 KiB bank bit is held high to create two mirrored 16 KiB banks. NROM mode requires MMC3 bank registers 6 and 7 specify two continuous 8 KiB banks and PRG A14 inversion in MMC3 register $8000 bit 6 to be disabled.

CHR-RAM Register ($6003, write)

Mask: probably $E003

D~7654 3210
  ---------
  L..P ....
  |  +------ CHR-RAM write-protect
  |           0=disabled, CHR-RAM write-enabled
  |           1=enabled, CHR-RAM write-protected
  +--------- Lock extra registers
              0=disabled, can write to $6000/$6003
              1=enabled, writes to $6000/$6003 ignored until next reset

Note

• The NROM and CHR registers function as a substitute for WRAM and can only be written to if $A001 bit 7 is set and $A001 bit 6 is clear.
• There may be registers at $6001 and $6002 as well, but the only game using this mapper does not access them.