A method and apparatus for using a control port in accordance with a variety of different protocols. A main processor communicates a configuration instruction to an interface controller. The interface controller uses the configuration instruction to select a protocol driver and to process signals to a control signal processor. The signals to the control signal processor include an output signal, an input signal, a direction signal, and a modulation enable signal. The control signal processor uses the direction signal to determine whether to output data or input data. The control signal processor uses the modulation enable signal to determine whether to couple a carrier signal on a transition from one digital level to another. The interface controller outputs data in accordance with a selected protocol and processes data input in accordance with the selected protocol.