| 摘要 |
PURPOSE:To allow even equipment connected to a private branch exchange which does not invert in polarity to detect an answer from the other party by providing a means which starts sending characters, speech, etc., when a ring- back tone is ceased after the ring-back tone is detected. CONSTITUTION:A CPU8 reads the dial number of an subscriber written in a memory 9 and sends the dial signal to a circuit 13 through a select signal generating circuit 11. When the transmission of the dial signal is completed, a connection detection relay 14 is placed in the contact state and a ring-back tone signal of 400Hz is detected by a band-pass filter 20 through a level adjusting circuit 19. The CPU8 detects the ceasing of the signal and knows that the opposite part answers, and turns off the connection detection relay 14 and connects a switch 12 to a modem 17 to start a communication. |
