Controller port pinout

The NES controller pinout:

       .-
 GND - |O\
 CLK - |OO\ - +5V
 OUT - |OO| - D3
  D0 - |OO| - D4
       '--'

The FC Twin NES/SNES combo clone uses Super NES controllers, whose pinout is as follows: (source: superfamicom.org)

 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 (leave D3 and D4 unconnected):

       .-
 GND - |7\
 CLK - |21\ - +5V
 OUT - |3O| - D3
  D0 - |4O| - D4
       '--'