Improving system integration by standardizing and automating the Modbus protocol

University essay from Luleå tekniska universitet/Digitala tjänster och system

Abstract: Communicating devices are on the rise. Fueled by the introduction of Internet-of-Thing (IoT) and Industry 4.0, more and more devices are capable of information sharing. There is a long history of communicating devices in industrial and building management contexts that previously relied on fieldbuses. One of these legacy fieldbuses is the Modbus protocol, originating in serial communication and now adapted for use with Ethernet. It has significant adoption in the fields of industrial automation systems (IAS) and building management systems (BMS) but carries many limitations. Industrial systems often have a long lifespan and fundamental changes are not introduced quickly. This leads to a need for legacy communication protocols to be able to function alongside the new paradigms for the foreseeable future. In order to facilitate this phase, an attempt to improve system integration in the Modbus context is performed in this thesis. By utilizing standardization and automation principles, additional functionality and definitions are proposed to the Modbus protocol to help improve system integration. By using interviews with system integrators and document reviews of available Modbus description documents three iterative development processes are performed to answer the research questions.  A proposed data model is presented, allowing for a standardized way to represent the contents of a Modbus register. Its attributes are clearly defined with descriptions and constraints. A new function code specification (0x47) is defined and presented in the same form as other function codes are described in the current Modbus specification. It allows for Modbus descriptors to be retrieved directly from the slave device. As a proof-of-concept the function code is developed in an existing Modbus implementation (Modbus4J). A client application is created to allow for fully functional demonstrations for a broader audience. The resulting communication is captured in Wireshark and presented as proof-of-concept.

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