| 摘要 |
PURPOSE:To judge the hook-up operation of master equipment in a house from a DC voltage by applying the DC voltage to a speech line only when the handset of the master equipment in the house is put off the hook for a communication between keeper's master equipment and the in-house master equipment. CONSTITUTION:When a keeper performs calling operation for the in-house master equipment 3, a CPU21 sends a call signal to a signal line 5 to perform a switching connection with speech lines 4A and 4B and the call time limiting timer incorporated in the CPU21 is set. The CPU31 of called in-house master equipment 3 connects a relay 32 to the speech lines 4A and 4B on the basis of its own address that said call signal contains and also generates a chime tone. When the handset of the in-house master equipment 3 is put off the hook, the DC voltage is applied to the speech lines 4A and 4B, so the CPU21 of the keeper's master equipment 2 resets the call time limiting timer on the basis of the hook-up detection output of a UD detecting circuit 23. |
