NES expansion port pinout

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Pinout of 48-pin NES expansion port

                                        +-------\
                                 +5V -- |01   48| -- +5V
                                 Gnd -- |02   47| -- Gnd
                            Audio in -> |03   46| -- NC
                                /NMI <- |04   45| -> out 2 ($4016 write data, bit 2)
                                 A15 <- |05   44| -> out 1 ($4016 write data, bit 1)
                                EXP9 ?? |06   43| -> out 0 ($4016 write data, bit 0, strobe on sticks)
                                EXP8 ?? |07   42| ?? EXP0
                                EXP7 ?? |08   41| ?? EXP1
                                EXP6 ?? |09   40| ?? EXP2
                                EXP5 ?? |10   39| ?? EXP3
($4017 read strobe) /OE for joypad 2 <- |11   38| ?? EXP4
                         joypad 1 D1 -> |12   37| -> /OE for joypad 1 ($4016 read strobe)
                         joypad 1 D3 xx |13   36| xx joypad 1 D4 (before inverting buffer)
                                /IRQ <> |14   35| xx joypad 1 D0 (likewise)
                         joypad 2 D2 -> |15   34| -> duplicate of pin 37
                         joypad 2 D3 xx |16   33| <- joypad 1 D2
                 duplicate of pin 11 <- |17   32| <> CPU D0
                         joypad 2 D4 xx |18   31| <> CPU D1
                         joypad 2 D0 xx |19   30| <> CPU D2
                         joypad 2 D1 -> |20   29| <> CPU D3
                           Video out <- |21   28| <> CPU D4
                           Audio out <- |22   27| <> CPU D5
       unregulated power adapter vdd -- |23   26| <> CPU D6
                     4.00MHz CIC CLK <- |24   25| <> CPU D7
                                        +-------/

Extra notes