| 摘要 |
PURPOSE:To use effectively a telephone set by cutting off forcibly a communicating state between a door phone and a button telephone set after a prescribed time and issuing an alarm to the telephone set in hooking-off so as to eliminate on convenience due to the hook-off after the end of the call with the door phone. CONSTITUTION:A subscriber connected to line terminal L1, L2 and a main trunk channel Ll are connected by a main trunk circuit SLC of a main device KSU and connected to an extension Li via a transformer T01 for talking current supply. Further, the extension INC detects a dial signal land callback tone. Then, the door phone DP and an electric lock EL are connected to the line L1 by a door phone circuit DPC and plural button telephone sets TEL1-TEL4 are connected to the line L1 by interfaces IF1-IF4. The device KSU is provided with amplifiers A01-A02, a calling generator CTG, an alarm tone generator ATG, and switch circuits AS01-AS03 so as to eliminate hook-off of the telephone sets TEL1-TEL4 after the end of a call with the door phone DP. |
