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Entry type: Application example Entry ID: 109474714, Entry date: 09/15/2017

Master-Slave Communication with Modbus RTU for S7-300 and ET 200S Systems

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This application demonstrates how the function of a Modbus RTU master as well as of several Modbus RTU slaves can be realized flexibly in an S7-300/ ET ET 200S automation system.

The application demonstrates

  • the configuration of the CP 341 as Modbus RTU master.
  • the configuration of the ET 200S 1SI module as Modbus RTU slave.
  • the technical program implementation of a Modbus RTU master and slave program in the S7-300 CPU in STEP 7 V5.5 and STEP 7 (TIA Portal).

The example is designed such that the RTU master program as well as the RTU slave programs are realized together in one S7-300 CPU. The Modbus RTU master communication module is the CP 341, the Modbus RTU slaves are realized with the 1SI communication modules of the ET 200S. Via the ET 200 S front module, these Modbus RTU slaves are in turn connected to the S7-300 CPU via PROFINET.

The following image shows the hardware structure of the example:

Figure 01

The advantage of this example is that both of the realized program parts, the Modbus master and the Modbus slave, are separable. The quantity structures (number of Modbus RTU slaves, data volume, etc) are also easily adjustable for your own applications.

Last change
Update to TIA Portal V14