| 摘要 |
An industrial control system has a central processing unit and a plurality of remote terminal units coupled to a communication network. Data is exchanged among the network devices in the form of messages which contain a source address, which designates the network address of the device that sent the message, and a destination address. Each of the remote terminal units stores a first network address assigned to the unit, and second network address corresponding to the network address of the originator of messages to which the remote terminal unit is to respond. The remote terminal unit processes only those messages in which both the destination address matches the first network address and the source address in the message matches the second network address. Thus multiple devices can be assigned the same first network address as long as each such device responds to a different source address. This enables more devices to be coupled to the network than the maximum number of allowable network addresses. Similarly multiple central processing units can be coupled to the network with access to a given remote terminal unit being restricted by the second address to messages originating from only one of the central processing units.
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