| 摘要 |
A direct inward-outward dialing (DIOD) trunk circuit having a DIOD detecting/sending circuit connected to tip and ring terminals connected to a central office line and a primary coil of a transformer, for detecting a polarity of the voltage potential at the tip and ring terminals and the current flowing therethrough to determine reception of one of an incoming and outgoing telephone call, and a switch, controlled by a relay driver responsive to an interface circuit used for interfacing the DIOD trunk circuit with a switching circuit of a private branch exchange (PBX), for enabling the current to flow between the tip and ring terminals through the DIOD detecting/sending circuit via one of a low or high impedance path, wherein the low impedance path is used to establish a speech path between a central office line subscriber and a corresponding extension subscriber of the PBX.
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