The Famicom's standard controllers are hardwired to the front of the unit, and a special 15-pin expansion port is commonly used for third-party controllers. The AV Famicom, however, features detachable controllers using the same ports as the NES.
The NES and Famicom have a set of I/O ports used for controllers and other peripherals, consisting of the following:
- One output port, 3 bits wide, accessible by writing the bottom 3 bits of $4016.
- The values latched by $4016/write appear on the OUT0-OUT2 output pins of the 2A03/07, where OUT0 is routed to the controller ports and OUT0-OUT2 to the expansion port on the NES.
- Two input ports, each 5 bits wide, accessible by reading the bottom 5 bits of $4016 and $4017. Reading $4016 and $4017 activates the /OE1 and /OE2 signals, respectively, which are routed to the controller ports and the expansion port.
- On the NES, only D0, D3, and D4 are connected to both controller ports, while all of D0-D4 are connected to the expansion port.
- On the original Famicom, the two ports differ: $4016 D0 and D2 and $4017 D0 are permanently connected to both controllers, while $4016 D1 and all of $4017's D0-D4 are connected to the expansion port.
- On the AV Famicom, only D0 is connected to the controller ports. The expansion port is unchanged.
- Controller port pinout