| 摘要 |
PURPOSE:To prevent unnecessary line holding after the end of call due to the hook-on state of the FAX communication, by discriminating the hook state of a telephone set with a false call current even after a line is connected to a facsimile (FAX) device, for attaining automatically the switching to the call state on the way of call. CONSTITUTION:Switches 4, 5 are selected as shown in figure at the call state, and a call current is detected with a hook-off detecting circuit comprising resistors 6a-6d and an inverter 9 and the like. The switches 4, 5 are selected at the call state and the hook state is detected with the false call current. A procedure interruption signal PRI-Q is transmitted under the depression of a telephone call button at the transmission side to receive the procedure interruption negative or affirmative signal PIN or PIP. If the device is failed, the line is changed over to the telephone set independently of the hook state of the telephone set. In receiving the signal PIN or PIP after the depression of call button, the state is monitored for a prescribed time and the line is switched automatically to the telephone set 3 when the hook-off is done. After the tranmission of the signal PIP or PIN at the receiving side, the hook-off state for a prescribed time is monitored and if the hook-off is not detected within a prescribed time, the line is interrupted. |
