1. Introduction With the development of control, computer, communication, and network technologies, a new control technology has emerged in the field of industrial control: fieldbus. Fieldbus is an open, fully digital, bidirectional, multi-station communication system established between the control system and field devices. Fieldbus systems have the following technical characteristics: system openness, interoperability and interchangeability, intelligent and self-sufficient functions of field devices, highly distributed system structure, and adaptability to the field environment. Many industrial control systems are characterized by multiple control points with long and dispersed distribution lines. Using fieldbus technology, the distributed I/O modules equipped in the control room and field consoles can be connected into a bus network, enabling serial transmission of control data digitally. This results in better anti-interference capabilities for the control system and more accurate reference values ​​provided to the frequency converter. A spinning mill adopted distributed control based on CC-Link fieldbus in its automated monitoring system upgrade project for spinning machines. The following section describes the construction of the CC-Link network and its characteristics in application, using a specific project as an example. 2. Spinning Machine Automation Monitoring System 2.1 System Upgrade The original electrical control system of this spinning mill used relays for logic control. Relay control employed hard-wiring, resulting in instability, a high failure rate, and difficulty in troubleshooting. The speed regulation system used analog control, with the rotational speed of each motor set using potentiometers and other analog signals. This resulted in insufficient accuracy, poor anti-interference capabilities, and inconvenient maintenance and debugging. The control system uses a Mitsubishi FX2N series PLC for logic control, enabling high-speed sampling and data processing in the control section. It exchanges data with the frequency converter via an FX2N-16CCL. To meet the needs of production monitoring and management, the system is equipped with a human-machine interface (GOT970). This device monitors production operation, including equipment status, fault alarms, and alarm history records. It also allows for appropriate modification and optimization of system parameters. The spinning machine's transmission system consists of a deacidification roller motor, a lifting shaft motor, and a pump roller motor, each driven by a separate frequency converter. These converters are all from Mitsubishi's FA500 series, possessing excellent static and dynamic characteristics and powerful network communication capabilities. They exchange data with the PLC via a CC-Link network. The CC-Link network allows the PLC to control each frequency converter, including starting, stopping, and setting its speed. Because the chemical gases generated in the spinning workshop can affect the lifespan of the frequency converters, they are initially required to be located outside the workshop, yet close-range operation is necessary inside. The electrical cabinets inside and outside the workshop are relatively far apart, but coordinated operation is required; that is, the operation of the frequency converters outside the workshop needs constant monitoring while operating inside. Using the CC-Link network easily solves this problem. 2.2 System Functional Flowchart This flowchart clearly shows the entire program execution process, thus illustrating the functions of the PLC and the touchscreen interface. The PLC primarily handles the control functions and parameter analysis and calculation of the entire system, while the touchscreen is responsible for setting parameters, dynamically displaying production data, and recording parameters. 3. CC-Link Fieldbus 3.1 CC-Link Characteristics CC-Link, short for Control & Communication Link, is an open fieldbus introduced by Mitsubishi Electric in 1996. It boasts a large data capacity and multi-level selectable communication speeds, up to 10Mbps. It is a composite, open, and highly adaptable network system, capable of accommodating networks ranging from higher management layers to lower sensing layers. CC-Link is a device-layer-based network, with each layer consisting of one master station and sixty-four slave stations. The master station is a PLC, while slave stations can be remote I/O modules, special function modules, local stations with CPUs and PLCs, human-machine interfaces, frequency converters, and various measuring instruments, valves, and other field instruments. Using a third-party gateway, connections from CC-Link to the ASI bus can also be achieved. 3.2 CC-Link Data Communication Methods CC-Link's underlying communication protocol follows RS485. Generally, CC-Link primarily uses a broadcast polling method for communication. CC-Link also supports instantaneous communication between the master station and local stations, as well as between smart device stations. Therefore, CC-Link communication methods can be divided into cyclic communication and instantaneous communication. The specific method of cyclic communication is as follows: The master station sends refresh data RY/RWw to all slave stations, while simultaneously polling slave station 1; slave station 1 responds to the polling from the master station with RX/RWr, and simultaneously informs other slave stations of this response; then the master station polls slave station 2 (while sending refresh data), slave station 2 responds, and informs other slave stations of this response; and so on, continuously cycling. In addition to the broadcast polling cyclic communication method, CC-Link also provides instantaneous information transmission functions between the master station, local station, and smart device stations. Information is transmitted from the master station to the slave station in 150-byte units. If information is transmitted from the slave station to the master station, each batch of information data is a maximum of 34 bytes. Instantaneous transmission requires a special instruction but does not affect the cyclic communication time. 4 System Software Design 4.1 Lower-Level Software Design The system control software was developed using Mitsubishi's GX Developer 7.0, which makes it easy to develop PLC process flow software. Before starting the fieldbus, a communication initialization program must be developed. First, in the parameter setting section, the number of modules connected to the entire system, the number of retries, the number of modules that automatically return, the operating rules (stop) when the CPU fails, and the information of each station are written to the corresponding addresses in the memory. After executing the refresh instruction, the parameters in the buffer memory are sent to the internal register area, thereby starting the data link. If the buffer memory parameters can start the data link normally, it means that the communication parameter settings are correct. At this time, the parameters can be stored in the E2PROM through the register instruction. This is because the parameters in the internal register will not be saved once the power is off, while the parameters in the E2PROM are still saved even if the power is off. At the same time, the communication parameters must be written to the E2PROM once, that is, only executed during initialization. After that, the CPU starts the data link by sending the parameters in the E2PROM to the internal register area. 4.2 Touch screen The touch screen uses GOT970, which is a computer with touch function and RS485 interface. It uses configuration software to configure the operation interface of transmission device and other equipment to be operated. There are four screens on the touch screen: main screen, parameter setting screen, independent operation screen and alarm screen. The main screen displays the number of revolutions of the spinning head, the parameters of the frequency converter and operation instructions of the equipment; the parameter setting screen is used to set the process parameters; the independent operation screen is used when debugging the equipment to display the operation status of each part of the equipment when working independently; the alarm screen displays the fault alarm information of the equipment. After configuration, the connection with the bus can be established by downloading. 5 Conclusion This control scheme based on fieldbus simplifies the system structure and makes the control system superior in design, installation, commissioning to normal production operation and maintenance. The main advantages are as follows: (1) Reduce the installation cost and maintenance cost of the control system. In the equipment production line or the entire control system, various field wiring and maintenance costs are reduced, the installation space of the control box is reduced, and the investment cost of the entire system is reduced. (2) Enhanced field-level information integration capabilities, enabling the acquisition of a wealth of information from field devices. The fieldbus digital communication network not only replaces 4-20mA signals but also transmits equipment status, fault, and parameter information. (3) Openness and interoperability increase the flexibility of system design and development. Products from different manufacturers are interoperable and interchangeable as long as they use a unified bus standard, thus the equipment has excellent integrability. (4) Improved system accuracy and reliability. The fieldbus-based automated monitoring system uses a bus connection method to replace one-to-one I/O connections, reducing unreliable factors caused by connection points. At the same time, the system has online fault diagnosis, alarm, and recording functions for field devices, and can complete remote parameter setting and modification of field devices, which also enhances the maintainability of the system.