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Deterministic timed bus access method

  • US 5,434,861 A
  • Filed: 02/04/1994
  • Issued: 07/18/1995
  • Est. Priority Date: 02/02/1989
  • Status: Expired due to Fees
First Claim
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1. A method of providing deterministic access to a bus structure having a plurality of nodes coupled thereto, in a data communications network, each node being capable of transmitting and receiving data packets to and from said bus structure respectively, and each node having a physical node address, which is defined as the address for said data packets, said method providing round robin scheduling of all nodes waiting to transmit data packets, and said method comprising the steps of,a) disposing a polling node, capable of generating a polling signal, defined as a timing reference signal, at a suitable point on the bus structure;

  • b) generating said timing reference signal which is independent of any data packets from said polling node to invite transmission of the data packets onto the bus structure after a period of silence;

    c) providing each node coupled to the bus structure with a unique predetermined time delay, defined as the node time delay, said node time delay starting from receipt of said timing reference signal and said time delay being fixed at network configuration time, which is prior to the start of normal transmission of data packets on the network, each said node time delay at a respective node being independent of said physical node address;

    d) detecting said timing reference signal at each said node as said timing reference signal travels along the bus structure, said timing reference signal being used by each of the nodes as the only timing reference signal to control its transmission activity onto the bus structure;

    e) including within each of said nodes two internal flags to control the operation of the node in respect of transmission of data packets, said flags being defined respectively as a Next Slot flag and a Transmit flag, the operation of each said nodes being such that transmission of a data packet onto the bus structure from an active node is permitted if the bus is silent at the expiration of said node time delay, providing that neither said Next Slot flag nor said Transmit flag is set, the method including the further steps of;

    i) setting said Next Shot flag, until the next timing reference signal is received by said node, if either said node does not have a data packet ready to transmit at the time it receives said timing reference signal or, if said node is unable to transmit a data packet when its said node time delay expires, as the bus is busy at that time,ii) setting said Transmit flag when said node starts to transmit a data packet;

    f) arranging that the said polling node generates the next said timing reference signal either;

    i) after said polling node has detected that the bus has gone silent after the end of a data packet orii) after said polling node has detected that a sufficient period of silence has elapsed for said polling node to know that no other nodes are going to transmit a data packet in response to the current timing reference signal;

    g) arranging that each of said Transmit flags in each of said nodes is reset when a said sufficient period of silence has elapsed that no other nodes are going to transmit a data packet in response to the current timing reference signal, andh) supporting communications for said data packets and said timing reference signals over a single shared bus structure such that data packets follow the timing reference signals in same shared data communications channel.

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