Support of Modbus TCP with STEP 7 V11 Service Pack 1 in the S7-1200

The S7-1200 PLC can now communicate to far more third party devices over Ethernet, thanks to enhancements delivered with STEP 7 V11 Service Pack 1.  Modbus TCP is now supported in the S7-1200 and requires no additional hardware.

Modbus TCP (Transmission Control Protocol) is a standard network communication protocol that uses the integrated PROFINET connector on the S7-1200 CPU for TCP/IP communication. Modbus TCP uses client-server connections as a Modbus communication path. Multiple client-server connections may exist, in addition to the already supported connections between other CPU’s, remote IO stations, HMI’s, STEP 7 software station and the CPU. Mixed client and server active connections are supported up to the maximum number of connections allowed by the CPU model.

Within the TIA Portal, Modbus TCP commands are included as standard instructions that require no additional licensing, and the handling is similar to what is already implemented for Modbus RTU.  It supports the following Modbus functions:

  • MB_CLIENT: Makes client-server TCP connection, sends command message, receives response, and controls the disconnection from the server.
  • MB_SERVER: Connects to a Modbus TCP client upon request, receives Modbus message, and sends response.

These enhancements allow for many more third-party gateways to also support this protocol. This is especially important for applications where the S7-1200 PLC needs to communicate to third-party devices that do not support the Profinet or Profibus protocols.

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