| 摘要 |
PURPOSE:To detect the response of a called subscriber independently of the connection polarity of a line by detecting whether the polarity is changed or not before and after a calling operation. CONSTITUTION:A relay contact 10 interrupts a line loop to transmit dial pulses. The output of a photocoupler 14 is sent to a called subscriber response detection signal line 20 through an inverter 16. This output is subjected to sample holding at two points of time of the automatic dialing operation by registers A17 and B18. It is discriminated whether contents of registers A and B coincide or not with each other by a coincidence detector 19, and the coincidence means that the response of the called subscriber does not exist, but the disaccord means that this response exists. Thus, since the response of the called subscriber is detected as a relative polarity change on the line, it is unnecessary to check the polarity at a line connection time, and the work is simplified. |
