Controller port pinout
From Nesdev wiki
The NES controller pinout:
.- GND -- |O\ CLK <- |OO\ -- +5V OUT <- |OO| <- D3 D0 -> |OO| <- D4 '--'
(Directions are relative to the jack on the front of the NES)
1 [oooo|ooo) 7 1:+5V 2:Clk 3:Out 4:D0 5:D1 6: I/O 7:Gnd
An adapter to use Super NES controllers on an NES (or NES controllers on an FC Twin) could be constructed as follows (leaving D3 and D4 unconnected):
.- GND -- |7\ CLK <- |21\ -- +5V OUT <- |3o| -- (D3) D0 -> |4o| -- (D4) '--'
- Buy two controller extension cables, one for NES and one for Super NES, and cut them apart. Strip the cut ends to reveal a small amount of bare wire.
- Using inline splice technique, wrap each wire from one cable with the corresponding wire from the other cable.
- With solder and a soldering iron, glue each wrapped pair together.
- With electrical tape, wrap each joint to insulate it from the other wires.
- Apply heat shrink around the whole assembly.
- The signal read by the CPU is logically inverted from the signal input on the D0-4 lines. A low voltage on D0 will be read as a 1 bit from $4016/4017.
- CLK will be low during reads from the CPU, then immediately return to high. This rising edge transition is used to clock the shift register inside the standard controller.
- OUT is a signal latched and held from the last CPU write to $4016:0. For standard controller reads, the program will write a 1 to load the shift register, then return to 0 before reading the results.