MMC6 pinout

                                        ___
                                       /   \
                                      /     \
                      (n) CPU A13 -> / 1  64 \ -> PRG A17 (r)
                              M2 -> / 2    63 \ <- CPU A14 (n)
                 (unknown, GND) -> / 3   O  62 \ -> PRG A18 (r)
                           n/c -- / 4        61 \ -> PRG A14 (r)
                          n/c -- / 5          60 \ -> PRG A15 (r)
                         /M2 <- / 6            59 \ -> PRG A13 (r)
             (unknown, GND) -> / 7              58 \ <- CPU A12 (nr)
             (unknown, 5V) -> / 8                57 \ -- GND
            (unknown, 5V) -> / 9                  56 \ -- VCC/batt
                VCC/batt -- / 10                   55 \ <- CPU A8 (nr)
                    GND -- / 11              ( )    54 \ <- CPU A7 (nr)
         (unknown, 5V) -> / 12                       53 \ <- CPU A9 (nr)
       3.3V Core Bias -- / 13                         52 \ <- CPU A6 (nr)
         (n) PPU A10 -> / 14                           51 \ <- CPU A5 (nr)
        (n) PPU A11 -> / 15                             50 \ -> PRG A16 (r)
PPU /RD || PPU A13 <- / 16                               49 \ <- CPU A4 (nr)    Orientation:
                     /             Nintendo MMC6             \                  --------------------
                     \      Package QFP-64, 0.8mm pitch      /                     48          33
       (r) CHR A10 <- \ 17                               48 / <- CPU A3 (nr)        |          |
        (r) CHR A16 <- \ 18                             47 / -> PRG /CE (r)        .------------.
         (r) CHR A11 <- \ 19                           46 / <- CPU A2 (nr)      49-|            |-32
          (n) PPU A12 -> \ 20                         45 / <> CPU D7 (nr)          |  Nintendo  |
           (r) CHR A13 <- \ 21    ( )                44 / <- CPU A1 (nr)           |O  MMC6B   O|
            (r) CHR A12 <- \ 22                     43 / <> CPU D6 (nr)            |            |
             (r) CHR A14 <- \ 23                   42 / <- CPU A0 (nr)          64-|o           |-17
                      GND -- \ 24                 41 / <> CPU D5 (nr)              \------------'
                  VCC/batt -- \ 25               40 / <> CPU D0 (nr)                |          |
                (r) CHR A15 <- \ 26             39 / <> CPU D4 (nr)                 1          16
               (n) CIRAM A10 <- \ 27           38 / -- VCC/batt
        (nr) CHR /OE, PPU /RD -> \ 28         37 / -- GND             Legend:
         (nr) CHR /CE, PPU A13 -> \ 29       36 / <> CPU D1 (nr)      ------------------------------
                    (r) CHR A17 <- \ 30     35 / <> CPU D3 (nr)       --[MMC6]-- Power
                        (n) /IRQ <- \ 31   34 / <> CPU D2 (nr)        ->[MMC6]<- MMC6 input
                      (n) /ROMSEL -> \ 32 33 / <- CPU R/W (n)         <-[MMC6]-> MMC6 output
                                      \     /                         <>[MMC6]<> Bidirectional
                                       \   /                          ??[MMC6]?? Unknown
                                        \ /                               n      NES connection
                                         V                                r      ROM chip connection

• GND pins (11,24,37,57) are internally connected to each other.
• VCC/batt pins (10,25,38,56) are internally connected to each other.
• All pins have internal protection diodes from GND and to VCC/batt except pins 4 and 5.
• Pins 4 and 5 measure infinite resistance to all other pins.
• Unknown input pins (3,7,8,9,12) are labeled per connections on NES-HKROM PCB.

Battery Circuit from NES-HKROM PCB:

   +------|>|----/\/\/------+------|<|-----O  NES 5V
+  |             1 kohm     |
  ---  3V                   |
 ----- Lithium              +--------------O  MMC6 VCC/Batt
   |   2032
-  |
   +---------------------------------------O  NES GND, MMC6 GND

3.3V Core Bias Circuit from NES-HKROM PCB:

           NES 5V  O----/\/\/----+
                       181 ohm   |
                                 |
                                 +-----O  MMC6 3.3V Core Bias
                                 |
                       470 ohm   |
NES GND, MMC6 GND  O----/\/\/----+

NES-HKROM (Startropics 1) BOM:

R1  1 kohm
R2  181 ohm
R3  470 ohm
C1  22uF 6.3V Electrolytic
C2  10nF Ceramic
C3  10nF Ceramic
D1  Diode (0.6V Forward)
D2  Diode (0.6V Forward)
U1  PRG-ROM
U2  CHR-ROM
U3  CIC
U4  MMC6
Batt 2032 3V Lithium