The PS and PS2 use a modified full duplex serial port with a 250 kHz clock signal for the controllers. The Gamecube uses a modified N64 half-duplex serial interface, right down to the 3.8 us timing.
Acimods contributor [Blizzrad] has just finished one of the cleanest mods we’ve seen in a while. With minimal modification to the outside of the PSP he was able to add an external PS2 controller. This ...