| 摘要 |
PURPOSE:To dispose communication terminals more than the number of terminal connections with a cheap constitution by providing a terminal extending unit capable of selectively connecting plural sets of the communication terminals to the terminal connecting parts of an exchange. CONSTITUTION:The terminal extending unit 5 is connected to a control signal terminal and a sound signal terminal of the terminal connecting part 2 of a main equipment 1 through a cable 3-1 and connected to the three extending communication terminals 7-1-7-3 through cables 6-1-6-3. When a calling is performed to a key telephone set 4 from the communication terminal 7-1, if an off hook is executed in the communication terminal 7-1, it is detected in an off hook detecting circuit 11 and a control circuit 14 in the terminal extending unit 5 transmits an off hook detecting signal to a control circuit 21 in the main equipment 1 through the control signal line of the cable 3-1. The control circuit 21 responds to this signal, if the communication terminals 7-2-7-3 are idle, and instructs to the control circuit 14 through the control signal line of the cable 3-1 so as to form the channel between the communication terminal 7-1 and the key telephone set 4 and switch a changeover switch 13.
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