Abstract: Objective To determine the elements of the communication protocol of Mitsubishi inverters and improve the reliability of the industrial speed control system constructed from them. Methods The communication protocol process of the control unit reading and writing inverter parameters is analyzed. Timing diagrams in Unified Modeling Language are used to describe the timing of communication with the Mitsubishi inverter. An example is given illustrating the communication process in the development of a speed control system composed of an AT89C51 microcontroller and a Mitsubishi inverter. Results The Mitsubishi inverter communication protocol is summarized into three elements: parameter initialization, communication data format, and communication timing, along with their contents and processes. Conclusion Understanding the Mitsubishi inverter communication protocol and clarifying the communication timing from these three elements is beneficial for developing a reliable speed control system. Keywords : Microcontroller; Mitsubishi inverter; Communication data format; Communication timing Mitsubishi inverters adopt the RS-485 bus standard, and their operating selection parameters, general flux control parameters, communication parameters, PID control parameters, and communication protocol are all open. Users can connect multiple frequency converters to fieldbus systems such as PROFIBUS and DeviceNet, and achieve network control through a monitoring computer to monitor their operating status and modify their parameters online, thereby greatly improving the intelligence of the frequency converter controller. Alternatively, a digital processor can be used to perform more complex calculations, resulting in more complete frequency conversion speed control performance and realizing a point-to-point control system composed of a digital processor and frequency converter, thus adapting to low-cost, single-frequency converter control methods. This article, combined with the development process of a Mitsubishi frequency converter control system using the AT89c51 microcontroller L4 as the digital processing core device, comprehensively introduces the specific content of the Mitsubishi frequency converter communication protocol from three aspects: initialization of communication parameters, communication data format, and communication timing between the microcontroller and the frequency converter. Finally, through a development example of a control system composed of a microcontroller and a Mitsubishi frequency converter, the communication process for reading and writing parameters is further described. [b][align=center]For more details, please click: Development and Application of Mitsubishi Frequency Converters Based on Microcontrollers[/align][/b]