== Technical ==
Basically, Pin8 needs to be swapped with Pin9 for the second joystick. However, the cable should also contain '''diodes''' in order to prevent conflicts between the two joysticks.
For example, if Player 1 moves UP-''and''-RIGHT then UP and RIGHT are shortcut with each other. In result, without the diodes, Player 2 would UP-''and''-RIGHT whenever trying to move UP-''or''-RIGHT.