NES 2.0 Mapper 534

NES 2.0 Mapper 534 denotes an MMC3-based multicart mapper with an optional (G)NROM-like mode.

• Atari Flashback Mini 7800
• 2-in-1 数独/五子棋 (NJ064) by Shenzhen Nanjing
• 18-in-1 Educational Computer by Zhuhai S.E.Z. Liming Electronic Co. Ltd.
• 8-in-1 (kk3311) by Waixing
• 8-in-1 (kk3314) by Waixing

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

These registers function identically to a normal MMC3, except that the scanline counter latch register ($C000) takes the inverted value (XOR $FF) compared to a regular MMC3.

Outer Bank/PRG Mask Register ($6800, write)

Mask: $E803

D~7654 3210
  ---------
  .N.C CPPp
   | | |||+- PRG A17 if N=1
   | | |++-- PRG A19..A18
   | +-+---- CHR A17..A18
   +-------- PRG A17 mode
              0: PRG A17=MMC3 PRG A17 (256 KiB inner PRG bank)
              1: PRG A17=p (128 KiB inner PRG bank)

Solder Pad Register ($6801, write)

Mask: $E803

D~7654 3210
  ---------
  .... ...M
          +- 0: CPU $8000-$FFFF reads PRG-ROM
             1: CPU $8000-$FFFF reads solder pad (D0/D1)

Inner CHR Bank Register ($6802, write)

Mask: $E803

D~7654 3210
  ---------
  .... CCCC
       ++++- CHR A16..A13 in GNROM mode,
             ignored otherwise

MMC3's CHR A10..A12 still apply, and therefore should be set up to form a contiguous 8 KiB bank.

Mode Register ($6803, write)

Mask: $E803

D~7654 3210
  ---------
  L..M ??N.
  |  |   +-- PRG A14 mode if L=1
  |  |        0: PRG A14=MMC3 PRG A14 (NROM-128)
  |  |        1: PRG A14=CPU A14 (NROM-256)
  |  +------ Banking mode
  |           0: MMC3 banking
  |           1: GNROM banking
  +--------- Lock registers $6800 and $6803

As was the case with similar mappers, GNROM banking is implemented by holding MMC3 clone's CPU A14 input is low, so that MMC3 registers #6 and #7 apply both to $8000/$C000 and $A000/$E000, and replacing the MMC3's PRG A14 with CPU A14 in NROM-256 mode (N=1).

Note

• Outer bank registers overlay any WRAM, and can only be written to if WRAM is enabled in the MMC3 ($A001=$80).
• Register $6802 is not affected by the Lock bit in register $6803.