Abstract : This paper introduces RS-485 communication between Mitsubishi FX series PLCs and Mitsubishi frequency converters. It analyzes in detail the hardware connection, frequency converter settings, and communication protocol for PLC-inverter communication, and provides application examples and PLC programs. Keywords : Programmable Logic Controller, Frequency Converter, RS-485 In the integrated application of PLCs and frequency converters, the traditional application generally uses the PLC's hard-contact output to control the operation and stop of the frequency converter, and uses multi-speed or D/A outputs to control the speed change of the frequency converter. In this application method, the PLC and frequency converter are connected through external wiring, and internal data transmission is not possible. However, using RS-485 communication control only requires a single communication cable connection, eliminating the need for other external wiring. It can not only perform all the functions of traditional applications but also perform internal data communication, conveniently obtaining various electrical parameters of the driven motor from the frequency converter, such as operating frequency, current, voltage, power, etc. With a human-machine interface (HMI), these electrical parameters can be directly displayed on the HMI. The following describes the RS-485 communication between Mitsubishi's FX series PLC and the Mitsubishi FR-S540 inverter. 1. Hardware Connection for PLC-Inverter Communication The Mitsubishi inverter has a port called PU, used to connect the inverter's operating unit. This PU port is an RS-485 interface. Using this interface, a host computer (PLC or computer) can perform operations such as reading and writing parameters, powering on and off, and changing the operating frequency of the inverter. The RS-485 interface uses differential input and differential output, providing strong anti-interference capabilities and making it very suitable for harsh field environments. Because of the RS-485 connection, one computer can control up to 32 inverters. Most computers only have an RS-232C interface; therefore, a 485 interface card or an RS-232C/RS-485 converter must be configured to connect to the inverter's PU port. [b][align=center]For details, please click: Communication between PLC and Frequency Inverter based on RS-485[/align][/b]