Abstract: A game controller is provided for controlling a portable processing system externally. The game controller may connect directly to the portable processing system or may connect to the portable processing system through an interface device. The interface device may patch memory locations of a ROM cartridge which contain a pointer to a memory location of the portable processing system which stores input from the built-in controls of the portable processing system. By matching these locations, input from the external controller may be provided to the portable processing system. Alternatively, a device which includes software executable by the portable processing system and external controls may be provided to operate in conjunction with the portable processing system. The software may be programmed to use input from the external controls instead of the built-in controls of the portable processing system.