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
- See Cartridge connector#Signal descriptions for notes about the ten EXP pins
- /NMI is an output because the PPU uses a push-pull driver, not open-drain signalling
- Joypad 1 and 2 D0, D3, and D4 are available as an input if no peripheral is connected to the corresponding joystick port that uses those bits:
- e.g. D0 is unavailable if e.g. a Standard controller or Four score is plugged in, and
- D3 and D4 are unavailable if a Zapper, Arkanoid controller, or Power Pad is plugged in.
