Device for monitoring the operation of a microprocessor system, or the like

A device for monitoring the operation of a microprocessor or the like, the device being capable of generating an error signal when the frequency of a signal derived from said microprocessor crosses a lower frequency threshold or an upper frequency threshold, wherein the device comprises:

• an oscillator capable of producing a periodic voltage which varies monotonically from a starting voltage, and including a threshold circuit to which said monotonically varying voltage is applied and which is capable of generating an error signal on an output of the device each time said monotonically varying voltage crosses a determined voltage threshold, said oscillator also including a reset input which, on receiving a reset pulse, serves to return the monotonically varying voltage to a level closer to its starting voltage;
• and
• a treatment circuit for treating the derived signal and capable of applying reset pulses to said reset input at a frequency equal to the frequency of the derived signal when said frequency is not greater than the upper frequency threshold, and to apply no reset pulse when the frequency of the derived signal exceeds said upper threshold frequency;
• the rate at which said monotonically varying voltage varies being such that when said reset pulses are produced at a frequency lower than said lower frequency threshold, the time interval between two successive reset pulses is greater than the time interval required for the monotonically varying voltage to go from the starting voltage to the threshold voltage.