NES expansion port pinout

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 |13   36| joypad 1 D4 (before inverting buffer)
                                 /IRQ |14   35| joypad 1 D0 (likewise)
                          joypad 2 D2 |15   34| duplicate of pin 37
                          joypad 2 D3 |16   33| joypad 1 D2
                  duplicate of pin 11 |17   32| CPU D0
                          joypad 2 D4 |18   31| CPU D1
                          joypad 2 D0 |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
                                      +-------/