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Computer Busses by William Buchanan

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18

Modbus

18.1 Modbus protocol

The Modbus protocol is an industry-standard protocol which allows programmable controllers to communicate over a network or local communications link. It defines a standard message structure that all Modbus-compatible controllers recognise and implement, regardless of the network type. It describes:

 The format of requests to Modbus-compatible devices.

 The format of responses from Modbus-compatible devices.

 The layout and contents of message fields for Modbus-compatible devices. The Modbus protocol provides the internal standard that the Modicon controllers use for parsing messages.

 How each controller knows its own device address and recognizes any messages addressed to it.

 The format of the data and other information ...

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