| 摘要 |
PURPOSE:To prevent the wasteful capture of a line wire by releasing a line after the lapse of the prescribed time of the holding warning tone of the line wire to recognize the lapse of holding the line wire. CONSTITUTION:Data is transmitted between a main equipment and a key telephone set 20. A line control circuit 30 connects any one of a telephone circuit network 32, a signal tone generating circuit 32 and a speaker circuit 38 to a line switching circuit 2 based on a signal from a control circuit 52. The control circuit 52, when the line wire holding is not cancelled after the lapse of the prescribed time t1 from the start of the line wire holding, starts the generation of the holding warning tone, gradually shortens the interval of the holding warning tone and releases the line when the line wire holding is not cancelled after the lapse of the prescribed time t2 after the start of the generation of the line wire holding.
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