| 摘要 |
PURPOSE:To input a hook-off simply to a microcomputer, by providing a hook- off detecting circuit at each subscriber. CONSTITUTION:In a subscriber 1, a handset is picked up and a hook switch 22 is hooked off, then a current flows to the 3rd relay coil 70 and relay contacts 72 and 73 are closed. Thus, terminals 40 and 41 go to 0V and this information is inputted to a central controller (MC) via an I/O circuit 11. The MC12 detects it and makes connection up to an outgoing register 9. After the connection, a terminal 27 goes to 0V with the outgoing register 9 and a current flows to the 2nd relay coil 60. Then, the 4th relay 80 is operative and the 3rd relay 70 is restored. In this case, the terminal 40 goes to 0V with a contact 84. When the subscriber 1 hooks on, since terminals 23 and 24 are opened, the 4th relay 80 is restored and the terminal 40 is returned to an open state. |
