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Entry type: FAQ Entry ID: 47756141, Entry date: 02/24/2017

How do you establish a MODBUS-RTU communication with STEP 7 (TIA Portal) for the SIMATIC S7-1200?

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  • Associated product(s)
The attached project and description give you a current example of communication via MODBUS RTU between two SIMATIC S7-1200 controllers.

The SIMATIC S7-1200 enables point-to-point communication via the CPU extension with the interfaces RS422/485 and RS232. Using the MODBUS library integrated in STEP 7 (TIA Portal) you can define each communication module as a MODBUS master or slave. If you select MODBUS Master, you can communicate

  • With only one slave using the CM 1241 RS232 (physical limitation).
  • With up to 10 slaves one after the other using the RS422 (via CM 1241 RS422/RS485).
  • With up to 32 slaves one after the other using the RS485 (via CM or CB 1241 RS485).

We will take the sample project to describe the configuration procedure in STEP 7 (TIA Portal)  for communication with multiple slaves using the CM 1241 RS422/485.

Fig. 1


Further Information
you will find in the following table:

Entry typeLink 
ManualSIMATIC S7 S7-1200 Programmable controller - Modbus RTU 
FAQWhich hardware and software components do you need to establish communication between SIMATIC S7 stations and third-party devices using the MODBUS RTU protocol? 
FAQHow can you read input words in the address range from 9999 to 65535 with the SIMATIC S7-1200/S7-1500 via Modbus RTU? 
ApplicationMaster-Slave Communication via a CM PtP using the Modbus RTU Protocol 

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