| 摘要 |
PURPOSE:To increase the functions as key telephone sets, by taking the trunk channel as the channel for door phones when the extension channel is in use and informing it to each telephone set when the extension channel and trunk channel are both in use. CONSTITUTION:With a callout switch 42 at a door phone 5, the information of door phone call is given to a control circuit 28 of a main device 2. (i); when the extension is vacant, a door phone channel 41 is connected to an extension channel 4 and a telephone set 6 with the route of SW36 contact 53-1 LPF18 capacitor 16. (ii); when the extension is in use, the door phone channel 41 is connected to a trunk line 3 via the route of SW36 contact 35-1 LPF17 capacitor 15 and connected to a channel 58 via contact 55-1 of the telephone set 6 contact 59-1. (iii); if the extension and the trunk line are both in use, an oscillator 68 in the telephone set 6 and a speaker 63 are connected with an SW69 to make tone call. |
