Importance

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Abstract

A control system for controlling an industrial process includes a network of a plurality of distributed programmable controllers or nodes coupled serially to a communications bus on either a single or dual media by means of a shielded twisted wire pair cable. The programmable controllers are coupled to the bus through a communications module which uses a broadcast method to achieve peer-to-peer communications. One module of the network, designated as an active monitor, exercises exclusive supervisory control of the broadcast activity on the network. The active monitor polls each node coupled to the network and each active node responds by broadcasting unacknowledged data to all nodes in the network. The broadcast message of each node in the network is mapped directly into designated variable memory locations of each programmable controller on the network. The active monitor establishes a list of active nodes based on the responses to the poll and allocates a time slot to each active node to broadcast its data and on a cyclical basis continues to poll a different node each network scan to update the list. Fault tolerance is provided by either an active-passive monitor arrangement for the single medium embodiment or by a redundant medium connection for the dual media embodiment.

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First Claim