Abstract: InterBus fieldbus, as one of the IEC 61158 standards, is widely used in manufacturing and machining industries. The material call control system in the automotive production process adopts InterBus fieldbus technology to restructure production logistics on the existing production line, fulfilling the enterprise's need for synchronized logistics. I. Introduction InterBus fieldbus, as one of the IEC 61158 standards, is an open serial bus system with high data transmission speed and efficiency. Its bus controllers and devices possess intelligence and strong fault diagnosis capabilities, making it widely used in manufacturing and machining industries. The material call control system in the automotive production process adopts InterBus fieldbus technology to restructure production logistics on the existing production line, fulfilling the enterprise's need for synchronized logistics. This system enables timely and efficient material supply, saves material storage space on the production line, reduces line-side and storage inventory, automatically calculates the workstations, times, and frequencies of material shortages, and effectively prevents unnecessary delays, waiting times, and line stoppages due to material shortages. The control system has online fault diagnosis capabilities, reducing system fault handling time and improving system reliability and factory production efficiency. II. Control System Composition The material call control system consists of hardware and software. The hardware mainly consists of an industrial control computer, a fieldbus controller, a BK bus coupler module, DIO and SAB digital input/output modules, an LED display screen, light boxes, and buttons. The fieldbus controller uses the RFC430, which has functions such as data acquisition, logic control, information exchange, and automatic diagnostics. The control system software consists of a control program and a fault diagnosis program. The control program functions as follows: According to automobile production requirements, when the production line inventory is below the minimum value, the production worker presses the corresponding button at the workstation. The bus controller, based on the returned process data, sends information such as the material name, workstation number, and quantity to the LED display screen via an InterBus fieldbus-based communication module. Simultaneously, a musical bell sounds and the corresponding indicator light on the light box is activated. After receiving the information, the warehouse staff presses the button below the indicator light on the light box to confirm the information and begin material feeding. Based on the confirmed information, the bus controller changes the indicator light above the workstation button from solid to flashing, indicating that the material is being fed. When the material arrives at the called workstation, the operator presses the button again, ending the material delivery process. Information such as the material name, calling station, calling time, arrival time, and feeder is recorded in the host computer's database and used as an indicator for management personnel to evaluate employees. The fault diagnosis program includes a diagnostic and self-starting program running on the controller and an OPC (OLE for Process Control) application running on the host computer (industrial control computer). Once the control system malfunctions, the bus stops operating. The online fault diagnosis program can quickly diagnose the cause of the fault and uses OPC technology to transmit the diagnostic information from the RFC430 bus controller to the host computer. Based on the diagnostic information transmitted by the controller, the host computer uses expert database technology to provide management with more detailed fault causes and solutions. Therefore, once the control system malfunctions, on-duty personnel can quickly troubleshoot the fault based on the fault diagnosis information and solutions. After the fault is resolved, the system can automatically restart the bus and resume normal operation. III. Diagnostic and Self-Starting Programs The standard registers in the InterBus bus controller RF430 provide bus operation status information and can also be used to operate the bus system through the control program. The standard registers in the bus controller include a diagnostic status register, a diagnostic parameter register, a standard function start register, a standard function status register, and a standard function parameter register. The register addresses can be set in the input or output address area of ​​the control system using the PC WORX configuration software for application in programming. The diagnostic status register is one word long, with each bit reflecting a certain aspect of the bus system's operating status. The diagnostic parameter register provides more detailed information about the status bits of the diagnostic status register. When peripheral devices malfunction or the bus fails, the diagnostic parameter register provides the error location; when the controller and bus fail, the diagnostic parameter register provides the error code. The diagnostic and self-starting programs are developed in the Program Worx functional programming software in PC WORX 2.02, using ST (Structured Text) language, and are then encapsulated into the functional module FCDIAG (see Figure 1). This module takes the diagnostic status register and diagnostic parameter register as inputs, processes them, and assigns the diagnostic information to the global external variables ERRDIAG STATUS and ERRDIAG_PAPA. The self-starting function can detect whether the fault has been cleared. Once the fault has been cleared, the bus is started through the standard function start register. IV. Application 1. OPC Data Access OPC is an object linking and embedding technology in process control. Based on the Component Object Model (COM) and Distributed Component Object Model (DOP) technologies, OPC adopts a client/server model and defines a set of COM objects and their interface standards. It is an interface standard in industrial control and production automation for connecting data sources (OPC servers) and data users (OPC applications). OPC data access methods mainly include synchronous access, asynchronous access, and subscription-based data acquisition. For asynchronous access, the OPC server returns a request from the OPC application almost immediately, and the OPC application does not need to wait and can handle other tasks. When the OPC server completes data access, it triggers an asynchronous access completion event in the OPC application, and the OPC application receives the data transmitted from the OPC server in its VB event handler. For subscription-based data acquisition, the OPC server also transmits data to the OPC application by triggering an event. 2. Diagnostic part of OPC application developed using Visual Basic (1) Variable declarations include OPCServer object, OPCGroups object, OPCCGruop object, OPCItems object and array ServerHandles_Bus() that stores server handles of OPC tags. The declarations are as follows: (2) Connect to the server and establish groups (3) Add tags (4) Data collection using subscription method. With subscription data collection, the OPC application does not need to issue a read request. When the OPC server finds that the data has changed, it automatically notifies and transmits the changed data to the OPC application side through the event objTestGrp_BusDataChange. The VB application obtains more detailed fault causes and their handling methods by querying the database based on the transmitted error information. The handling methods in the database are composed of expert experience knowledge and can be continuously updated and enriched. V. Conclusion Since the material call control system in the automobile production process was put into operation in 2003, it has been operating well and has achieved the expected control requirements. The implementation of this system has raised the company's logistics management to a new level and achieved good economic benefits. Online fault diagnosis in the control system improves the reliability of system operation, can greatly reduce the system's fault handling time, and helps to fully utilize the system's advantages.