| 摘要 |
A conventional watchdog timer circuit is arranged to judge a microcomputer to be normal as long as a pulse signal is being outputted from the microcomputer. Therefore, an abnormal condition cannot be detected when an operating frequency of the microcomputer lowers, for example. As a solution, the watchdog timer circuit is provided with a function for detecting the frequency. If the frequency of the pulse signal deviates from a predetermined frequency range, a reset signal is outputted indicating that the microcomputer is abnormal, even if the pulse signal is being outputted. A solenoid-operated gate valve is thereby closed to stop the supply of gas to a gas burner.
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