| 摘要 |
PURPOSE:To correctly perform prevention of collision of incoming and outgoing calls, regardless of the polarity of line connection, by detecting the inversion of polarity at each prescribed time, through a timer for line connection check. CONSTITUTION:A timer 31 for line connection check operates a polarity inversion detection section connection circuit 29 at waiting for each prescribed time. Thus, a contact 20cg is closed and the polarity check of lines is done at a polarity inversion detection section 4. When the polarity is inverted, a switch 32d is operated, and a timer 23 enters a rise incoming signal monitor state with an output of the timer 31. If the polarity inversion is not due to an incoming signal, since no output of an incoming signal detection section 7 is obtained, no switch 17b is activated, a fall signal of the timer 23 is inputted to a latch circuit 25 via an AND circuit 24 to activate a relay 26. Thus, contacts 27f, 28f are contacted and the polarity of lines L1, L2 is replaced. |
