I never noticed this till I started studding the schematics of the model 1 Megadrive/Genesis which is found here: http://emudocs.org/Genesis/mega1.png . It seems the EXT port found on the back of the early systems has the same pinout as the controller ports in the front. All of them connect to the same chip (315-5309 IC5). The only difference is pin 7 (Select) & pin 9 (Start) don't have resistors on their circuits like the controller ports do. Just wondering,would the Genesis see it as maybe a second,third or forth player or something else completely?