Patent ID: 8042009

Claim:
An electronic control device comprising: an arithmetic device that is a microprocessor having a watchdog timer circuit built in the microprocessor; and a runaway monitoring circuit that is an integrated IC externally connected to the microprocessor and that monitors the arithmetic device for an operational failure by receiving a pulse output from the arithmetic device; wherein the watchdog timer circuit or the runaway monitoring circuit detects occurrence of a failure of the arithmetic device according to a state of an indication signal which shows an operational state of the arithmetic device, when a runaway of the arithmetic device takes place after the arithmetic device is connected to a power supply and before a predetermined timer value is set in the watchdog timer circuit, the runaway monitoring circuit detects the runaway of the arithmetic device and resets the arithmetic device, the indication signal includes a wakeup signal which is sent from the arithmetic device to the runaway monitoring circuit, and a clear pulse signal which is sent from the arithmetic device to the watchdog timer circuit, and when a runaway of the arithmetic device causes the wakeup signal to be held at a low level and causes the clear pulse signal not to be output from the arithmetic device, operation of the runaway monitoring circuit is terminated while the wakeup signal is held at the low level, and the watchdog timer circuit counts a time while the clear pulse signal is not output and resets the arithmetic device when the counted time exceeds a predetermined time.