| 摘要 |
PURPOSE:To prevent tapping of a slave machine by giving an alarm at the time of detecting that a master machine cannot obtain the response from the slave machine because of takingaway of the slave machine to the outside of the service area of the master machine. CONSTITUTION:When detecting coming of a call period, a master machine 1 transmits a position confirmation signal. A slave machine receives this signal to transmit a response signal corresponding to the position confirmation signal. The master machine 1 starts a timer after transmission of the position confirmation signal and discriminates whether the timer expires at the time of reception of the response signal from the slave machine or not; and if it expires, an alarm 10 indicating that the position confirmation signal is not received is generated. Thus, the abnormality of the slave machine is detected.
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