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Dual master implied token communication system

  • US 4,988,990 A
  • Filed: 12/26/1989
  • Issued: 01/29/1991
  • Est. Priority Date: 05/09/1989
  • Status: Expired due to Fees
First Claim
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1. A method in a communication system in which only first and second master units send messages to and receive messages from at least one slave unit having a unique slave unit address over a common communications link, comprising:

  • for the first master unit;

    sending an initial message comprising the steps of;

    waiting for a clear channel on the communication link;

    setting a link quiet timer;

    enabling transmission of the initial message to the slave unit if a message from the slave unit to the second master unit is detected on the communication link;

    enabling transmission of the initial message if the link quiet timer times out and no transmissions have been detected on the communication link; and

    setting a link grant timer;

    sending subsequent messages comprising the steps of;

    enabling transmission of a subsequent message to the slave unit if the link grant timer times out and no messages from the second master unit have been detected on the communication link;

    setting the link quiet timer if a message from the second master unit is detected on the communication link and;

    enabling transmission of the subsequent message if a message from the slave unit to the second master unit is detected on the communication link;

    enabling transmission of the subsequent message if the link quiet timer times out and no messages have been detected on the communication link;

    setting the quiet timer and repeating the steps of sending subsequent messages;

    whereby as long as the second master unit does not transmit on the communication link, the first master nit transmits subsequent messages with only a delay of waiting for the link grant timer to time out;

    for the second master;

    sending an initial message comprising the steps of;

    waiting for a clear channel on the communication link;

    setting a link quiet timer;

    enabling transmission of the initial message to the slave unit if a message from the slave unit to the first master unit is detected on the communication link;

    enabling transmission of the initial message if the link quiet timer times out and no transmissions have been detected on the communication link; and

    setting a link grant timer;

    sending subsequent messages comprising the steps of;

    enabling transmission of a subsequent message to the slave unit if the link grant timer times out and no messages from the first master unit have been detected on the communication link;

    setting the link quiet timer if a message from the first master unit is detected on the communication link and;

    enabling transmission of the subsequent message if a message from the slave unit to the first master unit is detected on the communication link;

    enabling transmission of the subsequent message if the link quiet timer times out and no messages have been detected on the communication link;

    setting the quiet timer and repeating the steps of sending subsequent messages;

    whereby as long as the first master unit does not transmit on the communication link, the second master unit transmits subsequent messages with only a delay of waiting for the link grant timer to time out.

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