Abstract: This paper analyzes the basic characteristics and communication protocol of PROFIBUS-DP fieldbus, and introduces a design scheme of PROFIBUS-DP master system based on Hilscher embedded module COM-C, which is successfully applied in DCS system. Currently, the system is running stably and reliably in the field, achieving good practical results. Keywords: PROFIBUS-DP master; fieldbus; DCS system; embedded module 0 Introduction Fieldbus is one of the hot topics in the development of automation technology today, and is hailed as the computer local area network of the automation field. Its emergence marks the beginning of a new era in the field of industrial control technology and will have a significant impact on the development of this field. PROFIBUS (Process Fieldbus), as Europe's leading open fieldbus, has been accepted worldwide and has become an international open fieldbus standard. It is developing rapidly in China and is widely used in automation fields such as manufacturing and processes. Currently, more and more domestic automation equipment manufacturers have developed devices with PROFIBUS slave interfaces, which have gained widespread market recognition. However, there are very few independently developed devices with PROFIBUS master communication interfaces. This paper introduces a design scheme for a PROFIBUS-DP master system based on the embedded module COM-C. Products designed based on this scheme have been successfully applied in the WebField ECS-100 DCS system of Zhejiang Zhongkong. 1 PROFIBUS-DP Communication Protocol 1.1 Composition of PROFIBUS PROFIBUS is an open fieldbus standard launched by Siemens. It is a fieldbus standard of the German standard (DIN19245) and the European standard (EN50170), and has been incorporated into the international standard IEC 61158. PROFIBUS is an open digital communication system with a wide range of applications, particularly suitable for factory automation and process automation. PROFIBUS consists of three compatible parts: PROFIBUS-FMS, PROFIBUS-DP, and PROFIBUS-PA. PROFIBUS-FMS: Used for general control and communication tasks at the shop floor level, it is a token ring architecture, real-time multi-master network. PROFIBUS-DP: A high-speed and optimized communication solution, primarily used for communication between field-level control and distributed I/O and other field devices. PROFIBUS-PA: Designed specifically for process automation, compliant with intrinsic safety specifications, and suitable for applications in explosion-proof areas. These three layers of the PROFIBUS protocol make it the only fieldbus system capable of providing complete solutions for manufacturing automation, engineering automation, building automation, and power automation. 1.2 PROFIBUS-DP The PROFIBUS-DP protocol is designed for rapid data exchange at the field level. A central programmable controller (e.g., PLC, PC, or process control system) communicates with distributed field devices (e.g., I/O, drives, valves, or transmitters) via a fast serial connection. Based on the specific needs of various application areas, the basic functions of PROFIBUS-DP have been gradually expanded with special features. Currently, there are three versions: DP-V0, DP-V1, and DP-V2. Each version has its own dedicated key features, as shown in Figure 1. This difference in versions mainly reflects the chronological order of standardization work completed based on the ever-increasing application requirements. [align=center]Figure 1 Main functions of each version of PROFIBUS-DP[/align] DP-V0 provides basic DP functions, including cyclic data exchange, as well as station diagnostics, module diagnostics, and channel-specific diagnostics. DP-V1 includes functions added based on the needs of process automation, especially non-cyclic data communication for parameter assignment, operation, visualization of intelligent field devices, and alarm handling. In addition, DP-V1 has three additional alarm types: status alarms, refresh alarms, and manufacturer-specific alarms. DP-V2 includes other functions added mainly based on the needs of drive technology. Due to the added functions, such as isochronous synchronous slave mode and slave-to-slave communication, DP-V2 can also be implemented as a drive bus for controlling the rapid movement timing of drive shafts. 2. PROFIBUS-DP Master System Design PROFIBUS is an open standard, and in principle, the protocol can be implemented on any processor. Currently, automation manufacturers mainly use three solutions when developing PROFIBUS-DP master devices: 1. Software PROFIBUS Master: This solution implements the PROFIBUS protocol entirely in software, with a microprocessor running the complete protocol stack. This solution is particularly difficult and risky to develop, has a long development cycle, and requires developers to be extremely familiar with the PROFIBUS protocol and framework. After product development, it needs to be sent to Europe for protocol conformance testing and certification. 2. Dedicated ASIC chip plus extended firmware: This is a commonly used solution. A dedicated ASIC chip implements the media access control function of the PROFIBUS protocol data link layer; while other functions of the data link layer and application layer are implemented by the microprocessor running its extended firmware. However, firmware is currently difficult to purchase in the domestic market. If users write their own firmware, the difficulty increases, the development cycle is long, and it also needs to be sent to Europe for protocol conformance testing and certification. 3. Embedded Module Master Station: This is the most commonly used approach for developing PROFIBUS-DP master station devices. The module integrates a dedicated ASIC chip and firmware. This approach significantly reduces development difficulty and risk, shortens the development cycle, and the protocol has passed conformance testing and certification. This paper adopts the third approach—the embedded module master station—using the COM-CN-DPM (PROFIBUS-DP Master) embedded module from Hilscher Automation Systems GmbH, Germany. This module implements the PROFIBUS-DP master station protocol. The host system communicates with the module through the dual-port memory (DPM) interface provided by the embedded module. Users do not need to concern themselves with the specific implementation of the PROFIBUS protocol; they only need to read/write data to the DPM interface. Therefore, this module functions like a memory module, making it very convenient to use. 2.1 Hardware Design: The COM-CN-DPM embedded module provides users with two pin headers, X1 and X2. The X1 header (50 pins), the dual-port memory interface, includes the necessary control, data, and address lines for communication with the host. The X2 connector (30 pins) is the fieldbus interface, which includes PROFIBUS signal lines and LED status indicators. The embedded module COM-C interface circuit with the host is shown in Figure 2. Since the PROFIBUS protocol is implemented internally by the module, the user application only needs to perform read/write operations on the dual-port memory through the provided API interface and access method. The PROFIBUS signal lines are brought out through the fieldbus interface; simply connect a 9-pin D-Sub connector to the motherboard to connect the module to the PROFIBUS-DP network. The module also provides LED status indicators; the LED signal lines can be brought out to the motherboard for easy diagnosis of the module's communication status. [align=center] Figure 2 Embedded module and host interface circuit[/align] Since this module has integrated all the necessary circuits for implementing the PROFIBUS protocol, the peripheral circuit design is very simple and convenient; its circuit connection is similar to that of the MCU and memory. An Ethernet interface is also designed in this master station system for convenient remote file download. 2.2 Software Design The host interface provided by the embedded module COM-C is the dual-port memory DPM, which the user application accesses through the DPM interface. Meanwhile, to improve the real-time performance and reliability of the entire system, the host system uses the real-time multitasking operating system Linux. Therefore, the main focus of software design is on writing the driver program and application program. 2.2.1 Dual-Port Memory DPM Structure The dual-port memory DPM interface provided by the embedded module COM-C is an 8KByte address space, and its specific structure is shown in Figure 3. [align=center] Figure 3 Dual-Port Memory Address Space[/align] The user application accesses the PROFIBUS-DP master embedded module COM-C through the dual-port memory DPM. This dual-port memory is divided into two parts: protocol-independent (circular data address space) and protocol-dependent (non-circular data address space). Circular data contains the process image input and output data exchanged between the PROFIBUS-DP master and slave stations, while non-circular data contains parameters, messages, commands, status, and other data related to the PROFIBUS-DP protocol. l Process image output data: Output data sent by the host user program to the PROFIBUS-DP slave station. l Process image input data: Output data sent by the PROFIBUS-DP slave station to the host user program. * **Send Mailbox:** Non-cyclic message information sent by the host user program to the PROFIBUS-DP slave, including commands, diagnostics, and configuration file downloads. * **Receive Mailbox:** Non-cyclic message information sent by the PROFIBUS-DP slave to the host user program, including slave alarms, status updates, and configuration file uploads. * **Protocol Parameters:** PROFIBUS-DP protocol parameter information, including baud rate, watchdog time, and cycle time. * **Protocol Status:** PROFIBUS-DP network status information, including network status, errors, and timeouts. * **System Status:** Status information of the operating system running in the embedded module's COM-C and basic module information. * **Status/Handshake Flags:** Device initialization status information, process image input/output data, and mailbox message synchronization bits; writeable to the module, readable by the host application. * **Command/Handshake Flags:** User application status information, process image input/output data, and mailbox message synchronization bits; writeable to the host application, readable by the module. 2.2.2 Driver Design HIS provides Linux device drivers based on PCI, Compact-PCI, and ISA interfaces. In this system, the host CPU directly accesses the embedded module COM-C. Therefore, the provided Linux device driver code can be referenced and ported. The Linux device driver mainly completes the access to the dual-port memory of the embedded module COM-C, providing a general driver interface. User programs access the PROFIBUS master station embedded module COM-C by calling interface functions. The framework of the Linux device driver is shown in Figure 4. The advantage of this is that if other types of fieldbus (such as DeviceNet, CANopen) embedded modules COM-C from HIS are used in the future, the Linux device driver does not need to be changed and can be used directly. [align=center] Figure 4 Device Driver Framework[/align] The main functions implemented by the Linux device driver are shown in Table 1. Table 1 Linux Device Driver Function Table 2.2.3 Application Design The main functions implemented by the application are: remote reception and download of configuration files, transmission and reception of network data with the remote monitoring system, network monitoring, etc. The network configuration file generated by the network configuration tool SyCon can be exported as a DBM format file and then downloaded to the Flash memory of the embedded module via Mailbox (in message form). The configuration file download process is shown in Figure 5. [align=center] Figure 5 Configuration file download process[/align] Partial code is as follows: /＊＊＊＊＊ Download configuration file＊＊＊＊＊/ memset(&txMsg.data, 0, sizeof(txMsg.data)); /＊ Read relevant information from DBM file＊/ fseek(pfFile, 40, SEEK_SET); fread(&ul, 1, 4, pfFile); ……. usFileLength=＊(unsigned short＊)&txMsg.data[9]; usFileLength=（unsigned short）usFileLength＊2; memcpy(&txMsg.data[17], &abTemp[0], 34); /＊ Create first message＊/ txMsg.rx = 0x00; txMsg.tx = 0xff; txMsg.ln = 51; txMsg.nr = ++bNo; txMsg.a = 0; txMsg.f = 0; txMsg.b = 6; txMsg.e = 4; txMsg.data[0] = 3; if （ SendReceiveMessage（&txMsg, &rxMsg, 10000L）） goto LeaveProgram; fseek（pfFile, 44, SEEK_SET）; iRead=fread（&txMsg.data[0], 1, DOWNLOAD_LEN, pfFile）; usTransmittedLength = 0; /＊ If the maximum length of a message is exceeded, enter the loop and continuously send messages＊/ txMsg.ln = （unsigned char）（iRead）; txMsg.nr = ++bNo; txMsg.e = 8; do { usTransmittedLength+= (unsigned short)iRead; if ( SendReceiveMessage (&txMsg, &rxMsg, 1000L)) goto LeaveProgram; iRead=fread (&txMsg.data[0], 1, DOWNLOAD_LEN, pfFile); txMsg.ln = (unsigned char)iRead; txMsg.nr = ++bNo; txMsg.e = 8; } while (iRead == DOWNLOAD_LEN); /* Send the last message */ txMsg.e = 0xc; usTransmittedLength += (unsigned short) iRead; if ( SendReceiveMessage (&txMsg, &rxMsg, 15000L)) goto LeaveProgram; /＊＊＊＊＊ Download configuration file complete ********/ 3 Application of PROFIBUS-DP Master Station Module in DCS System The WebField series control system is a network-based control system launched by Zhejiang Supcon Technology Co., Ltd. to adapt to the development of network technology, especially Internet and Web technology. This system integrates the latest fieldbus technology, embedded software technology, advanced control technology, and network technology, achieving multi-bus compatibility and comprehensive integration of heterogeneous systems. Various domestic and foreign DCS, PLC, and field intelligent devices can be connected to the WebField series control system to realize the sharing of process control equipment information within the enterprise. The structure of the WebField series control system is shown in Figure 6. [align=center] Figure 6 System Structure Diagram[/align] As can be seen from the figure, the WebField series control system includes a four-layer network: management information network, operation network, process control network, and I/O bus. The management information network adopts general Ethernet technology for factory-level information transmission and management, serving as the information channel for comprehensive plant management. The operation network adopts Fast Ethernet technology to realize data communication between the server and client in C/S mode and time synchronization of operation network nodes. The process control network (SCnetII network) connects operator station nodes to the control station, enabling the transmission and sending of information and control commands. Its dual redundancy design ensures reliable and high-speed information transmission. The I/O bus is the internal communication network of the control station, including fieldbuses such as SBUS, PROFIBUS, Modbus, and DeviceNet. The PROFIBUS-DP master station system, based on a COM-C module, is one of the process control network nodes in the WebField series DCS. It solves the interconnection problem between the system and other manufacturers' measurement and control systems and intelligent devices, connecting standard PROFIBUS-DP slave devices to the system. PROFIBUS-PA devices can also be connected via connectors and couplers. Through the SCnetII communication protocol, process parameters from other manufacturers' measurement and control systems and intelligent devices can successfully communicate bidirectionally with the control station and operator station within the system, enabling configuration, management, display, operation, and calculation functions, thus making dissimilar devices part of the WebField series DCS. The PROFIBUS network configuration tool SyCon can be installed on the engineering workstation. Through the API functions provided by the SyCon configuration software, complete information sharing between PROFIBUS configuration and DCS configuration software can be achieved, thus realizing integrated configuration of the entire control system. The master station card developed based on the PROFIBUS-DP master station module has been successfully applied in the WebField series DCS, and redundant configuration can be performed in both the process control network and the PROFIBUS-DP network, ensuring the reliability of PROFIBUS network information transmission. To date, this PROFIBUS-DP master station card has been successfully applied in hundreds of fields. 4. Conclusion This paper, based on the research of the PROFIBUS-DP fieldbus communication protocol, proposes a highly reliable PROFIBUS-DP master station design scheme, which has been successfully applied in the DCS system and is now in stable and reliable operation, achieving excellent results. Currently, domestic manufacturers are mostly limited to system integration of foreign products and the development of PROFIBUS-DP slave products, with very little research and development on PROFIBUS-DP master station products. Therefore, this paper provides a reference for the development of PROFIBUS-DP master station products.