Microprocessor controlled safety monitor in motor vehicle - re-runs program to avoid erroneous operation due to parasitic disturbances

The program controlled monitoring system, such as a microprocursor system in a motor vehicle, can indicate an apparent failure due to parasitic disturbances. This is resolved by running the program again before operating any safety devices. The microprocessor controlled monitoring system (10) contains a monostable (101) whose inverting output is connected to another monostable (11). A JK bistable (13) acts as a coincidence detector whose output is connected via an OR gate (14) to a safety switch circuit (15). When the monitoring system monostable returns to its original state a short pulse is generated which passes via an RC circuit (18, 19) to a NAND gate (20). This causes the monitoring system to restart its program. An RC tuning circuit (22, 23) is switched from the monitor system to reset the JK bistable.