| 摘要 |
PURPOSE:To easily move a telephone set even during talking by allowing a master equipment side to apply holding automatically when the plug of the telephone set is disconnected and resetting the holding automatically when a telephone receptacle and the plug are connected again. CONSTITUTION:An impedance element 8 such as a resistor is provided to the plug 4 and when the plug 4 is mounted to the telephone receptacle 2, the insertion of the impedance element 8 is sent to a master equipment 6 via a control line 7. It is required to detect the disconnection and the insertion of the plug 4, and the impedance element 8 in the plug 4 and the 1st resistor 9 is the master equipment 6 connected in series with the said impedance element 8 at the insertion of the plug 4 are decided so that a voltage difference between the disconnection and the insertion is caused largest. The master equipment 6 detects the disconnection and connection of the plug 4 automatically by having only to plug in or disconnect the plug having the element to/from the telephone receptacle so as to set or reset the holding of an external line 5.
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