| 摘要 |
PURPOSE:To prevent illegal use without connecting an incoming call even if combinations of numbers are leaked by identifying the caller depending on the kind of a pushbutton signal and its sending time. CONSTITUTION:On receiving a call to a telephone line 100, an automatic reply circuit 101 replies the call automatically to urge the caller to send a pushbutton signal. In case of sending the pushbutton signal, a pushbutton signal detection circuit 102 detects its number and sending time and writes it in a storage circuit 3. When number of digits is coincident with the number of digits registered in the storage circuit 104, the storage circuit 104 is retrieved, the transmission time is compared as to the coincident number and when it is within a prescribed error, the connection signal is outputted to the switching circuit 106 to connect the line 100 to a master set circuit 107.
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