| 摘要 |
PURPOSE:To obtain the trunk-line trunk circuit of a PBX which can reduce a load on a processor by generating an acquisition signal which never performs unnecessary on-off operation during dial origination or termination. CONSTITUTION:When a ringing signal arrives from a station 1, a photocoupler 7 turns on and off synchronizing with the incoming signal. An interface circuit 8, on the other hand, holds a terminal BUSY at a level L by grounding a chip line 3 to turn on an LED9, thereby holding the driving signal terminal 10 of a relay K1 at a level H. A four-stage shift register 22 receives the output signal of an OR circuit 20 as a signal DATA to perform shifting operation by a signal CLOCK. The period of this signal CLOCK is selected by the output of the photocoupler 7 before the singal DATA moves to a terminal Q4 so that the contents of the shift register 22 are cleared, thereby holding an acquisition signal GDT' active. Dial origination is nearly the same. |
