1. A data processing apparatus comprising: at least one data input for receiving data, a processor for processing the data, the processor having at least one input, a data supply suppression unit connected between the data input and the at least one input suitable for suppressing or permitting supply of the data from the data input to the at least one input, and a control unit coupled to the data supply suppression unit for producing a control signal representing at least one operating condition or a quiescent condition for the processor, wherein the data supply suppression unit suppresses supply of the data from the data input to the at least one input when the control signal represents a quiescent condition for the processor.