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Modem Resynchronization Procedure for Multidrop Systems

IP.com Disclosure Number: IPCOM000085258D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Desblache, A: AUTHOR

Abstract

In multidrop systems, the modem associated with the master station must have a means of recognizing which tributary station is willing to send a message to the master station, in order to set its receiver before signaling the tributary station to transmit.

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Modem Resynchronization Procedure for Multidrop Systems

In multidrop systems, the modem associated with the master station must have a means of recognizing which tributary station is willing to send a message to the master station, in order to set its receiver before signaling the tributary station to transmit.

In this procedure, identification of the tributary station, resynchronization of the master modem and all associated functions are derived from the changes in a Pi pattern sequence sent by the tributary modem as a preliminary control signal. A Pi pattern sequence is a sequence of 180 degrees phase shifts of the carrier at every signaling period T.

Listed below is an example of such a procedure:

Sequence of operations of the emitter of the tributary modem:

1. Send Pi pattern of duration 15 T, T being the signaling

period.

2. Send a phase reversal of the Pi pattern.

3. Send a Pi pattern of duration (4+n)T; n being the

identification of the tributary station.

4. Send a phase reversal of the Pi pattern.

5. Terminate with a Pi pattern of duration 5T.

Sequence of operations of the receiver of the master modem:

1. 5T for automatic gain control (ACC) fast setting.

2. 10T for clock adjustment using the sinusoidal form of the

envelope.

3. Detect the first Pi pattern reversal and initiate tributary

count (one count per T).

4. Detect the second Pi pattern reversal and stop tributary

counter which provides the station number. Load the

equalizer tap values into the rece...