FILIPOVSKA, M. Investigation of MODBUS protocol latency in server-client scenario [online]. Brno: Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií. 2025.
The topic of this thesis was the optimisation of the implementation of the Modbus RTU communication protocol on a test model designed for controlling aviary windows. The window control system consists of a control unit (master) and up to 14 slave units, which communicate with each other using the mentioned protocol, but for some reason, the transfer speed is limited to 9600 Bd. The student's task was to find out the cause of the speed limitation and suggest a solution. The introduction describes the RS-485 bus and the Modbus RTU protocol, followed by a description of the hardware of the testing setup consisting of a master unit and two client units. This is followed by a description of the libraries for the Modbus protocol and its implementation in the CPU on both the client and server sides. The student designed a test setup to monitor the signals on the RS-485 bus and on the related microcontroller pins. For the measurements, she used a 16-channel Saleae logic analyser with PulseView software, which allows the analysis of various standard signals, including Modbus, and also detects signal jitter, for example. The result of numerous measurements and analysis of the obtained data refuted the original thesis that the low speed limit was caused by the low computing power of the 8-bit ATMEGA328P CPU on the client side. Surprisingly, it turned out that the isolated RS-485 bus driver of the MAX3157 type used on the server side causes a delay in the signals passing through it, resulting in the inversion of the bits of the transmitted messages. In conclusion, the student proposes improvements both at the hardware level and at the level of using other libraries for Modbus communication. During the semester, the student worked proactively and attended several consultations. The thesis is 48 pages long with 18 pages of appendices, which corresponds to the recommended length for a bachelor's thesis. In terms of presentation, the thesis is of a good standard and the text is well structured. From a formal point of view, the thesis deserves more attention, as the text is inconsistent in places and its quality is uneven. Despite the above shortcomings, I consider the assignment to have been fulfilled, as the student demonstrated very good creative abilities. In view of the above, I give a grade of 85 points.
The submitted bachelor thesis explores the latency characteristics of the Modbus RTU protocol in a server-client configuration using RS485 half-duplex communication. The student analysed a test setup consisting of one ESP32 client and two server units using low power Atmega chipset to evaluate the performance of various open-source Modbus RTU libraries across different baud rates. The Introduction chapter clearly outlines the motivation and scope of the thesis. It provides a solid overview of the Modbus protocol, differentiates between RTU and ASCII modes, and explains the rationale behind the hardware and software choices. The structure of the thesis is logical and well thought out: • Chapter 1 introduces the protocol fundamentals. • Chapter 2 presents the hardware setup and toolchain, discusses potential problem areas, and defines the methodology for testing and data collection. • Chapter 3 analyzes the behavior of four different libraries across a range of baud rates, with particular focus on performance degradation above 76800Bd. The practical part of the thesis is well executed. The student demonstrates a strong understanding of embedded systems and communication protocols. The experiments are relevant and lead to meaningful conclusions. The analysis of CRC failures, timeout behavior, and signal integrity at high baud rates is insightful. The student successfully identifies the limitations of both hardware and software components, and the final conclusions are supported by the collected data. However, the formal quality of the thesis is lacking. The text appears rushed in places, with inconsistent formatting, missing paragraph alignment, and insufficient referencing of figures. Several images, especially those showing data streams, are difficult to read and lack proper captions or explanations. These issues detract from the overall clarity and professionalism of the document. Despite these formal shortcomings, the thesis fulfills its objectives and provides valuable practical insights. The student has shown initiative, technical skill, and the ability to reflect critically on the results. Final evaluation: Grade: B (87 points) The thesis is technically sound and meets the requirements of a bachelor-level project, but would benefit from improved presentation and attention to detail.
eVSKP id 170066