Execution rate controlling device

Abstract

In order to control an execution rate of a central processing unit which carries out a processing operation in synchronism with a clock signal supplied from a clock oscillator, an execution rate controlling device periodically supplies a hold demand signal to suspend the processing operation during reception of the hold demand signal and comprises a data holding unit for holding held data representative of the execution rate. A generating unit generates the hold demand signal in response to the held data and the clock signal so that the hold demand signal may last for a duration which is inversely proportional to the execution rate. The generating unit comprises a counter unit for counting a count in synchronism with the clock signal up to a maximum value defining a period of periodic supply of the hold demand signal, and produces counted data indicative of the count and a carry signal initializing the count to zero when the count reaches the maximum value. A comparing unit compares the held data with the counted data and produces a coincidence signal when the held data and the counted data coincide with each other. A supplying unit supplies the hold demand signal to the central processing unit from a time instant of reception of the coincidence signal to a time instant of reception of a carry signal.