Abstract: In a data processing system a method and apparatus is provided for discriminating between digital signals of a plurality of different rates by monitoring the pulse width and repetition rate of such signals. The digital signals are continuously monitored to determine whether a single pulse or multiple pulses have been detected within a preselected time period. If only a single pulse or a portion thereof has been detected within the preselected time period a first type of control signal is generated. If multiple pulses or portions of multiple pulses have been detected within the preselected time period a second type of control signal is generated.