Siemens Industry Online Support
Siemens AG
Entry type: Application example Entry ID: 75867147, Entry date: 12/19/2018

Modbus/TCP - Standardized and redundant Communication of PCS 7 with Third-Party Systems

  • Entry
  • Associated product(s)
You can integrate controllers and systems of numerous manufactures with Modbus/TCP in PCS 7. Siemens provides an application example, in which a redundant Modbus/TCP connection is described completely.

Modbus is an open communication protocol that is used worldwide and supported by numerous manufacturers.
The requirement to connect third-party systems to SIMATIC PCS 7 via Modbus arises in particular when

  • legacy systems are expanded or modernized
  • controllers and systems from different manufacturers are connected – also when constructing new plants.

Modbus is based on a master/server or client/slave architecture that can be implemented in various ways within PCS 7.
On the one hand, the choice depends on the Modbus protocols (TCP or PtP) supported by the existing systems and controllers intended to communicate with one another.
On the other hand, the type of connection, i.e. which communication partner is the client and which one is the server, results from the plant network.

We introduce you to a Modbus/TCP library – available in different versions – that allows you to connect third-party systems to PCS 7 via Modbus/TCP.
A general description is followed by a configuration example that completely describes the Modbus/TCP client solutions for redundant connection of third-party systems to PCS 7 via Industrial Ethernet.
The example uses the "Modbus/TCP CP Red V4" Modbus/TCP library.

Video: Overview of the application

Customer benefits
This configuration example enables you to significantly reduce your engineering overhead using PCS 7 standard means and increase performance. You can use this solution for both new configurations and integration into existing projects.
All the necessary hardware and software products are from Siemens and ensure the usual compatibility, up-to-dateness and upgrade options. The solution considers both the PCS 7 standard and the Modbus standard without exception.
In addition, using the Modbus library provides you with the following advantages:

  • Easy connection of systems from different manufacturers to PCS 7 via Industrial Ethernet
  • Step-by-step, cost-effective expansion or modernization of legacy systems over their entire life cycle
  • Reliable support from Siemens
  • No specific Modbus know-how needed
  • Engineering in the familiar PCS 7 environment
  • Block library with online help in German and English
  • Setup in German and English

Main contents of the application description

  • Required hardware and software
  • Installation and setup
  • Configuration
  • Performance data
  • Add-on blocks: (send, receive, job management and diagnose)
  • PCS 7 message library

All Modbus blocks described and used in this application description are released for PCS 7 V9.x, V8.x and V7.1.

 Modbus/TCP Communication of PCS 7 with external systems 

Add-on blocks and PCS 7 message texts
Add-on blocks for Modbus/TCP communication

Further information
Modbus PtP - Redundant connection of third-party systems to PCS 7

Last revision
Update to PCS 7 V9.0

  • Interface changes of the Modbus/TCP blocks
  • New licensing model

Additional keywords

Security information
In order to protect technical infrastructures, systems, machines and networks against cyber threats, it is necessary to implement – and continuously maintain – a holistic, state-of-the-art IT security concept. Siemens’ products and solutions constitute one element of such a concept. For more information about cyber security, please visit