As disclosed in a patent document, Japanese Patent Laid-Open No. JP 2004-326629 A, (patent document 1) listed below, an abnormality monitoring device that monitors an abnormality of the microcomputer is known. The abnormality monitoring device includes an abnormality detector that detects an abnormality during a normal operation of the microcomputer and a standby disorder detector that detects a disorder during a standby time of the microcomputer.
The microcomputer outputs a watch dog pulse during the normal operation, and does not output the watch dog pulse during the standby time. Therefore, the abnormality detector determines that the microcomputer in the normal operation has an abnormality caused therein when the watch dog pulse is not input to the abnormality detector from the microcomputer for more than a preset period of time. The standby disorder detector determines that the microcomputer has a disorder caused therein when the watch dog pulse is input to the standby disorder detector from the microcomputer during the standby time of the microcomputer.
As described above, the standby disorder detector disclosed in the patent document 1 determines that the microcomputer has a disorder caused therein when the watch dog pulse is input to the standby disorder detector from the microcomputer during the standby time of the microcomputer. However, depending on a state of disorder of the microcomputer in the standby time, the microcomputer may possibly not output the watch dog pulse during the standby time (i.e., designated as a low power consumption mode, or a low power mode). Therefore, the abnormality monitoring device in the patent document 1 is not capable of detecting such a disorder of the microcomputer.