UNIVERSAL PBX LINE CIRCUIT FOR KEY AND NON-KEY SERVICE

摘要

A UNIVERSAL PBX LINE CIRCUIT FOR KEY AND NON-KEY SERVICE A line circuit for a time division switching PBX is disclosed which can serve conventional non-key telephone sets as well as pick-up key telephone sets having access to other telephone lines that may be served by prior art relay-operated key telephone line circuitry. The line circuit has a port appearance in the time division network and an electronic scan point for reporting the switchhook state of the associated telephone set. The circuit contains two, three-state flip-flops for correctly responding to the busy, idle or hold states that may be imposed by the associated telephone set and for distinguishing conventional A lead potentials when used with one or more conventional pick-up key telephone sets. No adjustment is required for operating with telephone sets that have no pick-up keys regardless of whether or not these sets maintain the A lead open-circuited or grounded.