Modbus/TCP Server

The Modbus/TCP server provides the possibility for Modbus/TCP clients to query data from a WinCC OA system and arrange the data within a Modbus data model. The accessible data is defined using a dedicated CNS view.

The server does not support distributed WinCC OA systems. Therefore, it can only connect to data points of the WinCC OA system in which the Modbus server runs.

The Modbus protocol is based on a master/slave topology. The master (client) is the unit which triggers a request. The slave (server) responses to the request and provides the appropriate data or performs the requested action.

The WinCC OA Modbus/TCP server opens a configurable TCP port (default 502) to which clients can connect. Each client connection must be configured since the Modbus/TCP server checks the connecting IP addresses/host names against its known IP address/host name list. This allows an access control mechanism as well as displaying client status data on predefined driver specific data points.

If the host name configured for a connection equals "*" all connecting clients will be accepted.

The WinCC OA Modbus/TCP server runs as a separate manager (WCCOAmodsrv) in the WinCC OA system. Several Modbus/TCP clients can be connected to one server. It is possible to run several Modbus/TCP servers in one project. The use of CNS views allows each server to provide different online data to its clients.

Depending on the memory area where the data is stored, it can be read/written by the appropriate function codes (FC). Refer to the chapters Modbus/TCP server details or How to access data for further information.