MMC3 pinout

Nintendo MMC3: 44-pin 0.8mm pitch QFP (Canonically mapper 4)

                             / \
                            / O \
                    n/c -- /01 44\ -> CHR A16 (r)
           (r) CHR A10 <- /02   43\ -> CHR A11 (r)
          (n) PPU A12 -> /03     42\ -> PRG RAM /WE (w)
         (n) PPU A11 -> /04       41\ -> PRG RAM +CE (w)
        (n) PPU A10 -> /05         40\ -- GND
               GND -- /06         \ 39\ <- CPU D3 (nrw)
      (r) CHR A13 <- /07           \ 38\ <- CPU D2 (nrw)
     (r) CHR A14 <- /08         \  _\ 37\ <- CPU D4 (nrw)
    (r) CHR A12 <- /09         \ \|    36\ <- CPU D1 (nrw)
 (n) CIRAM A10 <- /10           \ \     35\ <- CPU D5 (nrw)
  (r) CHR A15 <- /11         \  _\    o  34\ <- CPU D0 (nrw)
  (r) CHR A17 <- \12       /\ \|         33/ <- CPU D6 (nrw)
      (n) /IRQ <- \13        \ \        32/ <- CPU A0 (nrw)
    (n) /ROMSEL -> \14   /    \        31/ <- CPU D7 (nrw)
             GND -- \15  |_   /       30/ -> PRG RAM /CE (w)
              n/c -- \16   |         29/ <- M2 (n)
           (n) R/W -> \17  |/       28/ -- GND
        (r) PRG A15 <- \18         27/ -- VCC
         (r) PRG A13 <- \19       26/ -> PRG /CE (r)
          (n) CPU A14 -> \20     25/ -> PRG A17 (r)
           (r) PRG A16 <- \21   24/ <- CPU A13 (n)
            (r) PRG A14 <- \22 23/ -> PRG A18 (r)
                            \ O /
                             \ /

01, 16: both officially no connection. sometimes shorted to pin 02, 15 respectively

Note the orientation of the text: "MMC3" when viewed upright specifies pin 1 is bottom face, leftmost.

Mappers 37 and 47 connect pins 42 and 30 to a 74161

iNES Mapper 118 connects pin 12 to CIRAM A10, and pin 10 is n/c.

iNES Mapper 119 connects pin 44 to a 7432 and to the CHR RAM's +CE pin.

Pirate versions (600 mil 40-pin DIP package)

             .--\/--.                              .--\/--.                           .--\/--.
       M2 -> |01  40| -- VCC            /ROMSEL -> |01  40| -> WRAM /CE    CHR A13 <- |01  40| <- PPU A10
 WRAM /CE <- |02  39| -- NC             PRG /CE <- |02  39| -- VCC         CHR A14 <- |02  39| <- PPU A11
   CPU D7 -> |03  38| -> PRG /CE       WRAM /WE <- |03  38| -> WRAM +CE    CHR A12 <- |03  38| <- PPU A12
   CPU A0 -> |04  37| -> PRG A17        CPU A14 -> |04  37| <- CPU R/W   CIRAM A10 <- |04  37| -> CHR A10
   CPU D6 -> |05  36| <- CPU A13        CPU A13 -> |05  36| -> PRG A13     CHR A15 <- |05  36| -> CHR A16
   CPU D0 -> |06  35| -> PRG A18         CPU A0 -> |06  35| -> PRG A14     CHR A17 <- |06  35| -> CHR A11
   CPU D5 -> |07  34| -> PRG A14             M2 -> |07  34| -> PRG A15        /IRQ <- |07  34| -> WRAM +CE
   CPU D1 -> |08  33| -> PRG A16        PPU A12 -> |08  33| -> PRG A16     /ROMSEL -> |08  33| -> WRAM /WE
   CPU D4 -> |09  32| <- CPU A14           /IRQ <- |09  32| -> PRG A17         GND -- |09  32| -- GND
   CPU D2 -> |10  31| -> PRG A13      CIRAM A10 <- |10  31| -> PRG A18     CPU R/W -> |10  31| <- CPU D3
   CPU D3 -> |11  30| -> PRG A15        PPU A10 -> |11  30| -- NC          PRG A15 <- |11  30| <- CPU D2
 WRAM +CE <- |12  29| <- CPU R/W        PPU A11 -> |12  29| -> CHR A17     PRG A13 <- |12  29| <- CPU D4
 WRAM /WE <- |13  28| <- /ROMSEL         CPU D0 -> |13  28| -> CHR A16     CPU A14 -> |13  28| <- CPU D1
  CHR A11 <- |14  27| -> /IRQ            CPU D1 -> |14  27| -> CHR A15     PRG A16 <- |14  27| <- CPU D5
  CHR A16 <- |15  26| -> CHR A17         CPU D2 -> |15  26| -> CHR A14     PRG A14 <- |15  26| <- CPU D0
  CHR A10 <- |16  25| -> CHR A15         CPU D3 -> |16  25| -> CHR A13     PRG A18 <- |16  25| <- CPU D6
  PPU A12 -> |17  24| -> CIRAM A10       CPU D4 -> |17  24| -> CHR A12     CPU A13 -> |17  24| <- CPU A0
  PPU A11 -> |18  23| -> CHR A12         CPU D5 -> |18  23| -> CHR A11     PRG A17 <- |18  23| <- CPU D7
  PPU A10 -> |19  22| -> CHR A14         CPU D6 -> |19  22| -> CHR A10     PRG /CE <- |19  22| -> WRAM /CE
      GND -- |20  21| -> CHR A13            GND -- |20  21| <- CPU D7          VCC -- |20  21| <- M2
             `------'                              `------'                           '------'
            AX5202P #1                      AX5202P #2 / MC-3 (NTDEC's?)                 88

             .--\/--.                              .--\/--.
  CHR A10 <- |01  40| -- VCC            PPU A10 -> |01  40| -- VCC
  PPU A12 -> |02  39| -> CHR A16        PPU A11 -> |02  39| -> PRG A18?
  PPU A11 -> |03  38| -> CHR A11        PPU A12 -> |03  38| -> PRG A17?
  PPU A10 -> |04  37| -> WRAM +CE       CHR A10 <- |04  37| -> PRG A16 
  CHR A13 <- |05  36| -> WRAM /WE       CHR A11 <- |05  36| -> PRG A15 
  CHR A14 <- |06  35| <- CPU D3         CHR A12 <- |06  35| -> PRG A14
  CHR A12 <- |07  34| <- CPU D2         CHR A13 <- |07  34| -> PRG A13
CIRAM A10 <- |08  33| <- CPU D4         CHR A14 <- |08  33| <- CPU D7
  CHR A15 <- |09  32| <- CPU D1         CHR A15 <- |09  32| <- CPU D6
  CHR A17 <- |10  31| <- CPU D5         CHR A16 <- |10  31| <- CPU D5
     /IRQ -> |11  30| <- CPU D0        ?CHR A17 <- |11  30| <- CPU D4
  /ROMSEL -> |12  29| <- CPU D6         /ROMSEL -> |12  29| <- CPU D3
  CPU R/W -> |13  28| <- CPU A0         CPU R/W -> |13  28| <- CPU D2
  PRG A15 <- |14  27| <- CPU D7            /IRQ <- |14  27| <- CPU D1
  PRG A13 <- |15  26| -> WRAM /CE       CIR A10 <- |15  26| <- CPU D0
  CPU A14 -> |16  25| <- M2             CPU A0  -> |16  25| ?? ? 
  PRG A16 <- |17  24| -> PRG /CE        CPU A13 -> |17  24| -> PRG /CE
  PRG A14 <- |18  23| ??                CPU A14 -> |18  23| ?? ?
  PRG A18 <- |19  22| -> PRG A17             M2 -> |19  22| ?? ?
      GND -- |20  21| <- CPU A13            GND -- |20  21| ?? ?
             '------'                              '------'
               9112                                7903 9102

Notes:

• Those chips are fully compatible MMC3 clones that can be found in bootleg games (there might be minor differences like the PPU A12 edge on which the scanline counter is clocked).
• The connections to edge connector for single games are the same in both pirate and original version, although some pirate multicarts use those chips in non-standard way with different connections.
• There are reports that some lots of AX5202P contain a large number of factory seconds with the IRQ not working.
• AX5202P #1 and AX5202P #2 are confirmed to enable WRAM at $6000-$7fff at power up but protect them from writes (during CPU write cycle to $6000-$7fff when WRAM is protected, WRAM !CE and WRAM CE are not asserted). When RAM is disabled, open bus behavior is observed.
• NC seems to be not connected internally in both versions (multimeter diode test does not show any conducting voltage between NC and any other pins)
• AX5202P #1 is the one you can still buy nowadays (it has AX5202P marking).
• AX5202P #2 was found in at least one game - Doki Doki Yuuenchi bootleg (the chip does not have any markings)

References

• AX5202P #1: BBS
• AX5202P #2: BBS
• 88 BBS
• 9112 BBS
• 7903 9102 BBS