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Entry type: Application example Entry ID: 109747565, Entry date: 09/12/2017

Library for Modbus RTU (LMRTU)

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The "LMRTU" block library contains blocks for the communication via Modbus RTU with SIMATIC S7-1200 and S7-1500.

It comprises the following functions:

  • Scanning the bus for accessible slaves

  • Redundant communication with two CMs

Scanning the bus for accessible slaves
With the "LMRTU_Scan" function block, a Modbus master can scan the bus for accessible slaves. During operation, the master can thereby determine, if all known slaves are still accessible, or if new slaves have been added.

Redundant communication with two CMs
With the "LMRTU_RedMaster" function block, you can implement a redundant communication via Modbus RTU. For this, you add two CMs and interconnect the Modbus slaves as a ring.

If the bus is interrupted at one point and the slave cannot be accessed by the master CM any more, the FB tries to access the slave via the reserve CM.


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