INES Mapper 121

iNES Mapper 121 is used for the 卡聖 (Kǎshèng) A9711 and A9713 MMC3-clone-bearing protected boards.

A9711 (256 KiB PRG-ROM):

• MK6 (title screen hack of 幽☆遊☆白書 Final)
• Sonic & Knuckles 5 (hack of Somari, originally released by 哥德 (Gouder) on INES Mapper 116)
• Sonic 3D Blast 6 (hack of Somari, originally released by 哥德 (Gouder) on INES Mapper 116)
• Street Fighter Zero 2 '97 (not Street Fighter Zero 2)
• Super Real Bout 97 (hack of 餓狼伝説 Special, originally released by 哥德 (Gouder) on INES Mapper 116)
• The Panda Prince/Super Lion King 2/熊貓太子 (Xióngmāo Tàizǐ)
• Ultimate Mortal Kombat 3 (hack of Mortal Kombat 3)
• Ultimate Mortal Kombat 4 (hack of Mortal Kombat 3)
• 幽☆遊☆白書 97 V (Yū Yū Hakusho 97 V, title screen hack of 幽☆遊☆白書 Final)

A9713 (512 KiB PRG-ROM):

• 3-in-1: Earthworm Jim 2+4, The Lion King

Registers

Protection Array Read ($5000-$5FFF)

Mask: probably $F000

Returns the value from the four-byte protection array ($83, $83, $42, $00) indexed by the previous write to $5000-$5FFF.

Protection Array Index ($5000-$5FFF)

Mask: probably $F000

D~7654 3210
  ---------
  .... ..II
         ++- Select index into protection array on next $5000-$5FFF read

FCEUX' source code claims that address bit 8 switches between two protection arrays, the second one being $00, $02, $02, $03.

Outer Bank Register ($5180, A9713 only)

Mask: $F180

D~7654 3210
  ---------
  M... ....
  +--------- Select outer 256 KiB PRG-ROM and CHR-ROM bank

CHR A18 Control ($8000-$9FFF, even; A9711 only)

Mask: $E001

D~7654 3210
  ---------
  M... ....
  +--------- Select CHR A18 Mode
              0: CHR A18=inverted PPU A12
              1: CHR A18=PPU A12

On the A9711 board, either sprites or background tiles will come from the the second 256 KiB of CHR-ROM. Note that setting bit 7 will still also activate the MMC3 clone's CHR A12 inversion.

MMC3-compatible registers ($8000-$FFFF)

Mask: $E001, see MMC3.

Protection Latch ($8001)

Mask: $E003

If the previous write to the Protection Index register ($8003) selected indices $26, $28 or $2A, the value written to $8001 --- with the lower six bits reversed -- is immediately applied. Otherwise, it will only be applied upon the next write to the $8003. Regardless of the $8003 setting, the MMC3 clone will always receive the write as well.

Protection Index ($8003)

Mask: $E003

Bits 0-5 select a protection index register. If a valid index has been selected, the value previously written to $8001 --- with the lower six bits reversed --- is applied. If an invalid index has been selected, the $A000/$C000/$E000 banks selected via $8003 expire, and normal MMC3 PRG-ROM banking is restored.

• Index $26: Select 8 KiB PRG-ROM bank at CPU $E000-$FFFF using current bit-reversed $8001 value, and apply subsequent writes to $8001 to this index as well.
• Index $28: Select 8 KiB PRG-ROM bank at CPU $C000-$DFFF using current bit-reversed $8001 value, and apply subsequent writes to $8001 to this index as well.
• Index $2A: Select 8 KiB PRG-ROM bank at CPU $A000-$BFFF using current bit-reversed $8001 value, and apply subsequent writes to $8001 to this index as well.
• Index $2C: Select 8 KiB PRG-ROM bank at CPU $E000-$FFFF using current bit-reversed $8001 value if it is not zero, but do not apply subsequent writes to $8001 to this index.
• Index $2F: Do nothing, but keep the $A000/$C000/$E000 banks previously selected via $8003.
• Indices $20/$29/$2B/$3C/$3F: Select 8 KiB PRG-ROM bank at CPU $E000-$FFFF using current bit-reversed $8001 value, but do not apply subsequent writes to $8001 to this index.
• All other indices: Restore normal MMC3 PRG-ROM banking.

Writing to $8003 also has the side effect of writing the same value to the MMC clone's $8000 register.

Errata

• GoodNES 3.23b has several INES Mapper 121 images erroneously set to 187.

Similar Mappers

• iNES Mapper 187 has the same CHR A18 behavior as the A9711 board, adds an NROM override register, and drops the complex protection.