INES Mapper 164

iNES Mapper 164 denotes the ROM chipset of the 东达 (Dōngdá) PEC-9588 Pyramid Educational Computer that was later also used on the 燕城 (Yànchéng) cy2000-3 circuit board, used for the following games:

• Final Fantasy 太空戰士 V (G-003)
• 大話西游 (Dàhuà Xīyóu, G-004)
• 櫻桃小丸子 (Chibi Maruku-chan, G-005)
• 岳飛傳 (Yuèfēi Zhuàn, G-006)
• Dark Seed - 黑暗之蛊 (G-009)
• 口袋精靈: 金 (Pokémon: Gold Edition, not to be confused with several similarly-named ports of the same name)

Banks

• CPU $6000-$7FFF: 0-8 KiB unbanked PRG-RAM, not battery-backed
• CPU $8000-$BFFF: 16/32 KiB switchable PRG-ROM bank
• PPU $0000-$1FFF: 8 KiB unbanked CHR-RAM
• Nametable mirroring: hard-wired

The circuit board has address lines for 8 KiB of PRG-RAM, though all known carts mount either no or a 2 KiB RAM chip which is then mirrored three times across the respective address range. PRG-RAM is never battery-backed; all games save the game state to a 93C66 512-byte serial EEPROM. The EEPROM's "ORG" pin is tied to GND, selecting a word size of 8 bits.

Registers

All registers are initialized to $00 on reset.

PRG-ROM Bank Low/1 bpp Mode Switch ($5000, write)

Mask: $FF00

D~7654 3210
  ---------
  CSQM PPPp
  ||+|-++++- PRG A18..A14 if M=0
  || | ++++- PRG A18..A15 if M=1
  || +------ PRG banking mode
  ||          0: PRG A14..A18=QPPPp when CPU A14=0 (UxROM, 16 KiB switchable bank)
  ||             PRG A14..A18=11111 when CPU A14=1 and S=0 (fixed bank=1F)
  ||             PRG A14..A18=111p0 when CPU A14=1 and S=1 (fixed bank=1C or 1E)
  ||          1: PRG A14=CPU A14, PRG A15..A18=PPPp (BxROM, 32 KiB switchable bank)
  |+-------- See 'M' bit description
  +--------- 1 bpp video mode: when PPU A13=0 (pattern table) ...
              0: CHR A3=PPU A3, CHR A12=PPU A12 (disable 1 bpp mode)
              1: CHR A3=PPU A0, CHR A12=PPU A9, both latched on
                 last rise of PPU A13 (enable 1 bpp mode)

• 1 bpp mode is an all points-addressable video mode that allows the 8 KiB CHR-RAM to hold just enough data for an entire screen.
• Because this register is initialized to $00 on reset, thus clearing bit 4 which causes UxROM mode, the game's reset vectors will be at the end of 16 KiB bank #31.

PRG-ROM Bank High ($5100, write)

Mask: $FF00

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

Microwire Interface ($5200, write)

Mask: $FF00

D~7654 3210
  ---------
  ...S .C.D
     |  | +- 93C66 EEPROM DAT output
     |  +--- 93C66 EEPROM CLK output
     +------ 93C66 EEPROM CS output

Unknown ($5300, write)

Mask: $FF00

All games just write $00 to this register. Its meaning is certainly not the one seen in INES Mapper 162/163.

Microwire Interface ($5500, read)

Mask: $FF00

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

See also

• NES 2.0 Mapper 558 is a later version which drops UxROM mode and connects the microwire interface to EEPROM differently.