Method for synchronizing a digital communication system

Details Method for synchronizing a digital communication system Method for synchronizing a digital communication system

1987-11-17

1989-02-21

Griffin, Robert L.

Pulse or digital communications

Spread spectrum

Direct sequence

375109, 371 47, H04L 700

Patent

active

048072583

ABSTRACT:
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.

REFERENCES:
patent: 3813496 (1974-05-01), Maillet
patent: 3866172 (1975-02-01), Caron
patent: 4225960 (1980-09-01), Masters
patent: 4630284 (1986-12-01), Cooperman
patent: 4638473 (1987-01-01), Cooperman et al.
patent: 4691294 (1987-09-01), Humpleman
patent: 4727370 (1988-02-01), Shih
"Experimental Single-Chip PABX," IEEE Journal of Solid State Circuits, vol. SC-21, No. 2, Apr. 1986, pp. 247-251.

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