Expansion port

Both the NES and Famicom have expansion ports that allow peripheral devices to be connected to the system.

See also: Input devices

Famicom

The Famicom has a 15-pin (male) port on the front edge of the console.

Because its two default controllers were not removable like the NES, peripheral devices had to be attached through this expansion port, rather than through a controller port as on the NES.

This was commonly used for third party controllers, usually as a substitute for the built-in controllers, but sometimes also as a 3rd and 4th player.

Pinout

( Female DA-15 on peripheral )

                /\
               |   \
        Gnd -- | 01  \
               |   09 | -> /OE for joypad 2 ($4017 read strobe)
      SOUND <- | 02   |
               |   10 | -> out 2 ($4016 write data, bit 2)
       /IRQ ?? | 03   |
               |   11 | -> out 1 ($4016 write data, bit 1)
joypad 2 D4 -> | 04   |
               |   12 | -> out 0 ($4016 write data, bit 0, strobe on pads)
joypad 2 D3 -> | 05   |
               |   13 | <- joypad 1 D1
joypad 2 D2 -> | 06   |
               |   14 | -> /OE for joypad 1 ($4016 read strobe)
joypad 2 D1 -> | 07   |
               |   15 | -- +5V
joypad 2 D0 ?? | 08  /
               |   /
                \/

Signal descriptions

Digital inputs to the Famicom

Joypad 1 D1, Joypad 2 D1-D4

Digital outputs from the Famicom

Out 0, 1, 2; /OE for both joypads

Depends on cart

/IRQ (Some games use a push/pull driver, which doesn't permit anything else to disagree)

Analog outputs

SOUND (In the original Famicom, before expansion audio is mixed in. In the AV Famicom, after expansion audio is mixed in.)

Depends on model

Joypad 2 D0 (In the original Famicom, permanently connected to player 2 controller, so an output. On the AV Famicom, the player 2 controller could be removed, and allow for this to be an input)

NES

The NES has a 48-pin card edge located on the underside of the NES, beneath a plastic tab which must be cut or broken to expose the connector. The thickness of the connector is exceptionally thick (2.6mm), thicker than standard PCB thicknesses.

Because the NES had controller ports on the front that allowed different devices to be plugged in, the expansion port was a kind of "back up plan" for Nintendo that was never used commercially.

Pinout

                                        +-------\
                                 +5V -- |01   48| -- +5V
                                 Gnd -- |02   47| -- Gnd
                     Audio mix input -> |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
                                /IRQ <> |14   35| xx joypad 1 D0
                         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
                     Amplified audio <- |22   27| <> CPU D5
       unregulated power adapter vdd -- |23   26| <> CPU D6
                     4.00MHz CIC CLK <- |24   25| <> CPU D7
                                        +-------/

Extra notes

• All joypad input lines D0-4 are logically inverted before reaching the CPU. A high signal will be read as a 0 and vice versa.
• xx in above pinout: 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 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.
• /NMI is open-collector.
• /IRQ depends on the cartridge—most ASICs seem to use a push-pull driver instead of relying on the pull-up resistor inside the console.
  • Because of this, a series 1kΩ resistor should be included to safely use the /IRQ signal in the expansion port.
  • This resistor is enough to logically overcome the internal 10kΩ pull-up, and will also limit any ASIC's output-high current to 5mA if your expansion device tries to drive it low at the same time.
• See EXP pins for notes about the ten EXP pins.
• See Standard controller and Controller port pinout for more information about controller connections.