| 摘要 |
PURPOSE:To form quickly a loop of a talking circuit in an off-hook mode and to assure the assured transmission of dial pulses, by controlling the 1st transistor (TR) with the voltage of a talking circuit control terminal of a push- button type DP signal transmitting dial control circuit. CONSTITUTION:In an off-hook instant, a resistance R1 a diode D4 the base of a TR Q2 and then TRs Q1 and Q2 are successively turned on. Then a trunk loop is closed through a talking circuit NW. While an IC completes its resetting when the terminal Vdd exceeds the threshold voltage of the IC and a reset signal received the time control by a reset circuit RS2 is applied to a reset terminal HS. Then a talking circuit control terminal M is set at ''H'', and therefore the base current which is supplied to a diode D2 a resistance R5 a resistance R11 and then a TR Q8 is prevented by the OFF of a TR Q3. The TR Q8 is finally kept off; while both TRs Q1 and Q2 are kept on respectively. |
