Implementation of Modbus TCP protocol SNC-42 data acquisition device

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Dr. Csubák Tibor
Department of Control Engineering and Information Technology

In the past few years, several generations of industrial data acquisition systems had been developed at the Department of Control Engineering and Information Technology of the Budapest University of Technology and Economics. As a result of the development in the past few years, a highly versatile product line has been created, which is suitable for small data acquisition tasks with some input signals or to create a large, complex data acquisition system.

The main tasks of the SNC-42 device are to integrate the data acquisition systems into the higher level business control system, to provide remote management functionalities to them and to provide supervisory functions to the local technological staff with the use of the integrated HMI interface. The device already has a very wide set of communication abilities, but the used solutions are not standardized. Because of this it was necessary to expand these abilities, with a new standardized and widely used protocol. By these requirements the Modbus TCP protocol was selected. As a result of my developments during this term, the device can be integrated into SCADA systems with the use of the implemented Modbus TCP server.

In the first part of my thesis, I present the most widely used members of the Modbus protocol family. After the review of the internal workings of the SNC, I present the synthesis of the used data structures, and how they can be mapped to Modbus registers. In the next chapters I present the usage of completed Modbus TCP server, and introduce the revealed problems and the used solutions for them. Finally, as an ending of my paper, I write about the improvement possibilities.


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