| 摘要 |
In a ringing control circuit having a plurality of subscriber line circuits (LC0 through LC3) and a single ring trip circuit A (or a ringing loop-current detector) which operates commonly to all the subscriber line circuits (LC0 through LC3), an AND circuit (44) is provided in each subscriber line circuit (LC0 through LC3) for stopping the ringing operation by the subscriber line circuit. The ringing operation is initiated by said subscriber line circuit (LC0 through LC3), and is stopped when the subscriber lifts a handset. The AND circuit (44) stops the ringing operation upon reception of an answer detection signal from the ring trip circuit A indicating the lifting operation of a handset together with the phased ringing signal for the related subscriber. Thus, even when one subscriber lifts a handset, the ringing signals of other subscribers are not stopped, in spite of a single common ring trip circuit A. Thus, a central control unit does not need to re-energize a ringing operation of those subscribers which do not answer, when said ring trip circuit A provides an answer detection signal (a).
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