| 摘要 |
PURPOSE:To avoid the transmittion of an urging signal in case of limitless short distance call in a public telephone set. CONSTITUTION:With a dial signal from a public telephone set 5, a signal corresponding to charaging signal is incoming from an exchanger 2 to a call line 7a in case of a long distance call. When a signal reception circuit 12 receives this signal, output is given to a discrimination circuit 14 and a gate circuit 15. Since no polarity inversion is made before the response of a called party, no output is given from a line polarity detection circuit 13, but when a charging signal is transmitted after the response, since the circuit 13 causes an output, the charging signal is given to an urging signal detection circuit 16 through the gate circuit 15, and when the residual is lower than the one call's share, an urging signal is transmitted. In case of a limitless short distance call, since no signal corresponding to the charging signal before the polarity inversion is incoming, no output is produced from the circuit 14 and no urging signal is transmitted even if a charging pulse is incoming after the response of the called party. |
