Abstract: A device for monitoring the operation of a microprocessor and capable of generating an error signal whenever the frequency of a signal derived from the microprocessor crosses an upper or a lower frequency threshold comprises: an oscillator periodically producing a monotonically varying voltage and including a threshold circuit, the oscillator generating an error signal when the monotonically varying voltage crosses a threshold, and including a reset input for returning the monotonically varying voltage to level closer to its starting voltage; and a treatment circuit for treating the derived signal and generating pulses on the input at the frequency of the derived signal so long as the frequency is no greater than the upper threshold, otherwise applying no pulse to the input. When pulses are produced at a lower frequency, the time interval between two reset pulses is greater than the time interval required for the monotonically varying voltage to reach the threshold voltage.