Abstract: A highly distributed industrial control system employs a number of separate control modules communicating together on a shared communications medium. Each module emulates one or more basic electrical parts having electrical terminals, such as switches and relays, and transmits production messages indicating the state of the parts, such as conducting current or not. A connection list for each part in each control module defines message identifiers of other parts whose production messages are received by the control module and interpreted as current flow to one or more of its parts. The control system is programmed by generating a schematic on a programming terminal showing connections of terminals on symbols of the parts such as would represent actual wiring of the emulated parts. This schematic is analyzed to determine the immediate upstream neighbors of each part and the message identifiers of those parts in the control modules form the connection lists.

Abstract: Each message carried by a communication network has a packet that contains data, a tag, and a generation count wherein duplicate packets sent in different messages have identical generation counts. A station includes a modem that connects to the communication network in order to receive messages. A fixed screener circuit has a first memory that stores a set of tag values and a fixed screener determines when a packet tag matches a tag value in the first memory. The station also has an interface through which tag values are received from an external device, such as a host computer. A general purpose screener includes a second memory with a plurality of storage locations in which to store tag values from the interface and a generation count associated with each tag value.