发明授权
US5142571A Digital telephone set having an emergency switching function and communication system having the same 失效
具有紧急切换功能的数字电话机和具有该紧急切换功能的通信系统

Digital telephone set having an emergency switching function and
communication system having the same
摘要:
A digital telephone set includes a digital telephone circuit and an emergency analog circuit. Normally, the digital telephone circuit is made active so that a handset provided in common therewith is connected to a digital transmission line. In an emergency, the emergency analog circuit is made active instead of the digital telephone circuit so that the handset is connected to an analog transmission line. A dial key pad unit and a speaker are provided in common with the digital telephone circuit and the emergency analog circuit.
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