| 摘要 |
PROBLEM TO BE SOLVED: To provide an interphone system where errors such as a program runaway in a microcomputer can surely be recognized. SOLUTION: This interphone system is provided with a microcomputer 1, that stores programs for various operating processing in its built-in memory and applies timer processing to the programs to provide an output of pulses having a prescribed period, a watchdog circuit 9 that receives the output signal from the microcomputer 1 and outputs a normal signal, when the received signal is a pulse signal outputted from the prescribed period and outputs an abnormity signal, when the received signal is other than the pulse signal, and an LED 10 that makes displays different from those of normal signals or the abnormal signals outputted from the watchdog circuit 9.
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