Apparatus and method for bidirectional data communication in a game port

Abstract

A game port interface is disclosed which permits bidirectional communication between a game port and a peripheral device. In one embodiment, the peripheral device is a digital joystick and the game port sends commands to the digital joystick. The game port interface includes one or more timers whose inputs are coupled to resistances within the joystick. Also coupled to the timer inputs are capacitors such that the resistors in the joystick form a charging network with the capacitors in the game port interface. When an output instruction to the game port is executed, the capacitors coupled to the timer inputs are charged to a predetermined voltage. The timer input is also coupled to an inverter within the joystick. The output of the inverter switches to a low logic level when the timer input is charged above a logic threshold. The output of the inverter is coupled to an interrupt input on a microprocessor within the joystick. The microprocessor interprets one or more interrupts as commands and takes appropriate action. In one embodiment, the first interrupt causes the digital joystick to transmit data corresponding to the position of the joystick. If a second interrupt is transmitted to the joystick while the first interrupt is being processed, the second interrupt is interpreted as a second command. Each interrupt transmitted to the joystick while the joystick is processing the previous interrupt is interpreted as a new command. For example, if the joystick is processing the second interrupt, and a third interrupt request is detected at the interrupt input, this is interpreted as a third command. The digital joystick of the present invention is also capable of operating in an analog emulation mode. The game port can send similar commands using the interrupt circuitry described above to the joystick while in the analog emulation mode.