| 摘要 |
PURPOSE:To call a caller by separating a calling channel while connecting a caller to the line DC-wise as it is by operating a mute circuit at the time of calling between telephone sets connected to the same line, and separating the calling circuit from the line. CONSTITUTION:When a caller-side telephone set 310 is hooked off, an exchange 101 inverses the polarities of a line 1 and a line 2 respectively to 'negative' and 'positive'. After receiving a dial number, the exchange 101 temporarily turns the said polarities respectively to 'positive' and 'negative' in order to recognize the caller-side telephone set 310. In the telephone 3 a loop same as that for waiting is formed, and the exchange 101 recognizes the telephone 310. When the exchange 101 returns the polarities of the lines 1 and 2 to original ones, the transistor 14 of an erasing circuit 100 turns ON for a prescribed time, and the calling circuit 21 is separated from the line, however, a transistor 18 continues the closing of a DC loop instead of it.
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