| 摘要 |
PURPOSE:To attain talking with high quality by connecting a circuit with a line as an object the sending of a selection signal via a low impedance circuit only while a selection signal of key telephone system is sent and disconnecting the circuit from the line at the time of other talking. CONSTITUTION:A resistor R2, a diode D2 and a capacitor C1 in a low impedance circuit 10 at talking are disconnected from the line and only R1, D1, C1 forming a high impedance circuit are connected to the line and a minute current flowing to a R1 stores an electric charge to the capacitor C1 gradually. When a talker hooks off and desires dialing to depress a keyboard 9 to send a selection signal, a dialer IC8 detects the key depression, is started by the charge stored in the C1 and the selection signal transmission is started and an XMVTE reaches a GND level. Thus, a Tr1 is turned off, Tr2, Tr3 are turned on and low imped ance R2, D2 are connected to the VDD to acquire the current to operate consecu tively to the dialer IC from the line. |
