| 摘要 |
PURPOSE:To attain sure automatic incoming processing by providing a line switch disconnecting a telephone set from a telephone line in a short time before the operation of an incoming display ring circuit when a line polarity detector detects the polarity inversion so as to prevent erroneous off-hook of a telephone set. CONSTITUTION:When a call comes from the caller side when a network control unit is set to the automatic incoming mode, the polarity of a telephone line 1 is inverted and the inversion is detected by the line polarity detector 5. When the polarity of line is inverted, a line switch 7 disconnects the telephone set from the telephone line 1 by the switch control of the detector 5 before ringing within 0.3sec Although the telephone set does not ring by the disconnection from the line 1, an incoming display ring circuit 6 informs the presence of an incoming call to a person. After the detection of incoming for 3sec by the detector 5, the switch of the line switch 2 is switched by the control of the detector 5 to connect the line 1 to a MODEM 3 for the automatic incoming processing and a data communication terminal equipment 4 applied data communication.
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