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112 Estimating Network Performance

890 USE 100 00

3.23 Sample Communications Across Networks

Figure 44 shows two controllers on separate Modbus Plus networks

joined by a bridge. Each controller has its own peer processor. The

bridge has a separate peer processor for each network. Each network

has a separate token rotation pattern and timing.

CONTROLLER

PEER

PROCESSOR

CONTROLLER

PEER

PROCESSOR

NETWORK A NETWORK B

PEER

PROCESSOR

PEER

PROCESSOR

BRIDGE

REQUEST >

< RESPONSE

REQUEST >

< RESPONSE

Figure 44 Sample READ Communication Across Networks

During the ladder logic scan in unit A, an MSTR block is executed that

specifies a read request to unit B. At the end of the block execution, the

read request is sent to the peer processor in unit A. The following

events occur:

Step 1 When the peer processor in unit A acquires the network token, it

transmits the read request. The peer processor in the bridge sends an

immediate acknowledgement.

Step 2 When the bridge has the token on network B, it transmits the read

request to unit B. The peer processor in unit B sends an immediate

acknowledgement to the bridge.

Step 3 At the end of the ladder logic scan in unit B, the incoming

transactions are handled. The peer processor in unit B is ready with

the data response to the read request.

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Schneider Electric Modbus Plus Network Bridge Multiplexer none Guia de Instalação Página 127