Introduction Programmable Logic Controllers (PLCs) evolved from early relay logic control systems. Since their introduction in the 1960s, PLCs have experienced rapid development, particularly in data processing, network communication, and integration with distributed control systems (DCS). PLCs have become a powerful tool for industrial automation, widely adopted and applied. This article uses a traffic signal control system as an example, focusing on the communication between a PLC and the host computer's industrial control configuration software, KingSCADA. 1. FX-ON-60MR PLC and its programming software MELSEC-F FX Applications The FXON series from Mitsubishi Corporation of Japan is a high-performance micro programmable controller launched in recent years. It features a compact and aesthetically pleasing design, powerful functionality, and flexible system configuration. Users can select various basic units, as well as appropriate expansion units and modules, to flexibly and conveniently configure the system according to control requirements, forming control systems with different I/O points and functions. Various configurations offer excellent performance-price ratios. The FXON series has strong communication capabilities and can communicate with devices with built-in RS-232C communication interfaces. Mitsubishi's FX series programming software, MELSEC-F FX Applications, is a PC programming software that allows programming in both ladder logic and instruction list languages. After programming, the program is transferred to the PLC via a dedicated F2-232C AB type RS232C cable. 2. KingSCADA V6.0: KingSCADA is an integrated Human-Machine Interface (HMI) and monitoring management system that can communicate with various external devices such as programmable logic controllers (PLCs), intelligent modules, smart instruments, and remote data acquisition devices (RTV). Its software system is independent of the user's final field equipment. For different hardware, users only need to follow the installation wizard to configure the I/O devices and install the corresponding hardware drivers for the communication devices. The hardware device drivers then handle the communication between KingSCADA and the I/O devices. During system operation, KingSCADA uses its embedded device management program to exchange data with the I/O devices in real time. 3. Traffic Light Control System: The traffic light control system controls the red, yellow, and green traffic lights at intersections. The control requirements are as follows: When the start button is pressed, the traffic lights begin to operate. The east-west green light illuminates for 56 seconds, while the north-south red light illuminates for 60 seconds. After the east-west green light illuminates for 56 seconds, it flashes for 2 seconds, then transitions to the east-west yellow light, which illuminates for 2 seconds. Afterward, the east-west red light illuminates for 60 seconds, the north-south green light illuminates for 56 seconds, flashes for 2 seconds, and then the yellow light illuminates for 2 seconds before turning off. The I/O allocation is as follows: Input/Output Start X0 East-West Green Light Y1 North-South Red Light Y5 Stop X1 East-West Yellow Light Y2 North-South Green Light Y6 East-West Red Light Y3 North-South Yellow Light Y7 Partial control program is shown in Figure 1. 4. Communication between PLC and Host Computer (KingSCADA Software) Communication between the PLC and the host computer can be achieved using high-level programming languages. However, users must be familiar with the interconnected PLCs and the communication protocols used in the PLC network, and strictly adhere to the communication protocol specifications when writing communication programs for the computer. This places high demands on the user. Using industrial control configuration software to achieve communication between the PLC and the host computer is relatively simpler because industrial control configuration software generally provides communication drivers for relevant devices. For example, Siemens S7 series PLCs can be connected to WinCC industrial control configuration software to achieve communication between the PLC and the host computer. The following describes the steps for implementing communication between KingSCADA 6.0 and the FX-ON-60MR PLC. The FX-ON-60MR PLC uses RS232 or RS422 for communication, occupying one serial port on the computer. Without adding an expansion card, communication with the computer can be achieved using the programming port. First, connect the device using the F2-232CAB RS232C cable (dedicated to PLC and computer). Connect the PLC to the host computer's serial port (COM port) via its programming port for serial communication. The serial communication method uses the serial port of the "KingSCADA computer," and the I/O device is connected to the serial port of the "KingSCADA computer" via an RS-232 serial communication cable. Second, configure the device in the project directory display area of ​​the KingSCADA project browser. Click on the serial port (COM port) connecting the PLC and the host computer under the "Device" outline to set the parameters. For FX series PLC programming port COM port parameter settings: Then, double-click the "New" icon corresponding to the set COM port in the KingSCADA browser directory display area. The "Device Configuration Wizard" dialog box will pop up. Complete the device settings for communication with KingSCADA in this dialog box. The device configuration wizard allows for the installation of serial communication I/O devices; the installation process is simple and convenient. During configuration, users need to select the manufacturer, model, and connection method of the I/O device, assign a logical device name, and set the device address (FX series PLCs do not require a device address when communicating via the programming port). Third, construct the database. The database is the core of the "KingSCADA" software. In the project manager, select "Database\Data Dictionary," double-click the "New" icon, and the "Variable Properties" dialog box will pop up. Define the corresponding registers for the FX-0N-60MR PLC: Italicized words such as dddo, dddd, and ddd represent the variable parts in the format, where d represents a decimal number and o represents an octal number. The range of variation is listed in the value range. KingSCADA reads the corresponding data from the lower-level machine according to the register name. The registers defined in KingSCADA correspond to all registers on the lower-level machine. Defining an illegal register will not be recognized. If the defined register does not exist in the specific lower-level machine model used, no data will be read. Fourth, design the graphical interface and establish animation connections. Create a control diagram of red, yellow, and green traffic lights at a crossroads on the KingSCADA "screen" (see Figure 2). Create start and stop buttons, and associate each control signal light and the start and stop buttons with the corresponding variables to establish animation connections. Fifth, run the system. Start the KingSCADA system TOUCHVIEW and run the traffic light control. Set the PLC switch to the "RUN" state, press the start button, and observe the control results of the traffic light system. Experimental results show that the system runs normally and the animation effect is good. 5. Conclusion. The application of PLC and multi-machine PLC combined with computer network communication is increasing. It combines the advantages of computers and PLCs. The computer, as the host computer, provides a good human-machine interface for monitoring and managing the entire system. The PLC, as the slave computer, performs reliable and effective distributed control. The method of using industrial control configuration software to realize communication between PLC and host computer is simple and easy to implement. It reduces the requirements for users, greatly shortens the design cycle, and has good system inheritance. This advantage is even more prominent for large-scale complex control systems.