| 摘要 |
PURPOSE:To prevent the call without charge, by cutting off the call when the charging signal sent from the exchange can not be received. CONSTITUTION:When the toll call incoming detection signal PR produces ''H'' output from the toll call identifying circuit 3, the clock pulse CP is input to the timer circuit 51 through the AND circuit 52. When the charging signal is incoming within the specified time after the operation of the timer circuit 51, one pulse ''L'' as the charging signal incoming detection signal is input to the flip-flop 4 from the signal processing circuit 22, the output is taken as L and the timer circuit 51 is reset. Thus, since the timer output D is not produced, no cut-off output is caused. If no charging signal is input within the specified time, the timer circuit 51 advances the count, the cut-off output is produced and the call channel is disconnected with the relay GS. |
