Abstract : This paper proposes a design concept and specific implementation for the communication part of a multi-frequency converter system composed of a frequency converter controller with the ADMCF328 as the core DSP control chip, using an S7-200 series P1C module for centralized control. The specific communication protocol, key technical problems to be solved during implementation and their solutions, and some implementation code examples are given. Keywords : PLC, frequency converter, communication protocol, RS-485 interface 1 Introduction In industrial applications, a system often consists of multiple motors. Each motor is usually driven by a controller, requiring centralized control of these frequency converter controllers. This system uses a self-developed frequency converter, with the core chip of its control part being the ADMCF328 DSP chip from Analog Devices. It uses the CPU226 module from the SIEMENS SIMATIC S7-200 series PLC for centralized control, employing a custom communication protocol that is simple and reliable. This system has already been used in practical industrial applications. This paper introduces the design and implementation of the communication part of this system. 2 System Structure The structure of the system is shown in Figure 1. 1) The CPU226 module is a SIEMENS PLC module with 24-bit input and 16-bit output. It has two RS-485 ports, one of which connects to the TD200, and the other connects to the RS-485 bus controlling multiple frequency converters. 2) The TD200 is a Chinese text display used to display and modify the control parameters in the CPU226 module. [b][align=center]For details, please click: Design and Implementation of the Communication Section of a Multi-Frequency Converter System Controlled by S7-200[/align][/b]