| 摘要 |
PURPOSE:To transmit quickly and accurately a dial pulse by providing two off- hook detecting circuits independently for both incoming and outgoing calls, therefore preventing a malfunction due to a ringer signal, and also performing the off-hook detection in an outgoing call mode with no delay. CONSTITUTION:If a control circuit 1 of a hook state detecting circuit detects an off-hook state when an external incoming call is detected, the output of a ringer signal generating circuit 2 is produced at the output of an AND gate 12 and outputted to an output terminal 10 via an LPF3 and an insulated transformer 4. In such a case, a switch 17 is turned off by a control line 8 to inhibit the actuation of a photocoupler 11. While a current is supplied to a photocoupler 7 by a ringer signal, and malfunctions are prevented by the output fed from a delay circuit 6. Then the off-hook information is outputted to a transmission line 9. The switch 17 is turned on with a call fed from an own end office. Thus the coupler 11 is actuated. Then the off-hook information is outputted to the line 9 from the terminal 10 via the coupler 11 and an AND gate 16. While the dial information is outputted from a dial pulse control circuit 13. |
