Gte Laboratories Incorporated

David A Perreault

Richard W Sieber

Arnold Paige

In a digital communication system including a central PABX subsystem coupled by a transmission line to a remote telephone subsystem, a method for establishing synchronization between the PABX and the telephone. The data format includes a message transmitted from the PABX to the telephone during the first half of a frame and a response transmitted from the telephone to the PABX during the second half of the frame. The synchronization method includes the steps of recognizing that synchronization has been lost, discontinuing transmission of responses by placing the line driver in a high impedance state while continuing transmission of messages, and detecting a valid message on the transmission line. The valid message is detected by finding in sequence, a message stop bit, the stop bit remaining on the line for one half frame and a message start bit. When a valid message is detected, transmission of responses is resumed.

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Reading, MA, United States of America

David A Perreault