| 摘要 |
PURPOSE:To simplify a circuit, and to reduce the number of parts, by sending out a dial pulse by making intermittently a switching relay by a network control circuit, and detecting the hook state of a telephone set by the network control circuit. CONSTITUTION:In a manual outgoing, an operator transmits a continuous dial signal, and changes a mode to a transmission mode by operating switching relays 20 and 21, when an opposite answers a telephone. In an automatic outgoing, the operator drives the switching relays 20 and 21 by controlling a network control circuit 30, then sets the mode at the data transmission mode. The telephone set is cut off from a line by the operation of the switching relay 21, and a telephone set 5 is connected between +5V and the earth. Therefore, since a potential at a point (x) goes to the earth when the telephone set is set in a hook-off state, and to +5V in a hook-on state, the network control circuit 5 can discriminate the hook-on/off state of the telephone set 5 by the potential at the point (x).
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