Abstract: This paper introduces Profibus-DP and a pure master-slave communication fieldbus network constructed using its communication interface module. The network configuration is achieved through the dedicated networking tool SYCON. Finally, with a minitype boiler as the application object, the Network approaches the monitoring of all the controlled objects in the system. Keywords: Profibus -DP fieldbus; master node; network configuration 0 Introduction The Profibus fieldbus consists of three compatible parts, namely PROFIBUS-DP, PROFIBUS-PA, and PROFIBUS-FMS: (1) PROFIBUS-DP: used for communication between the device-level control system and distributed I/O. Its design is intended for high-speed data transmission at the device level. (2) PROFIBUS-PA: Designed for process automation, it allows sensors and actuators to be connected on a single bus and has intrinsic safety specifications. (3) PROFIBUS-FMS: Used for workshop-level monitoring networks, it is a token-structured, real-time multi-master-slave network. Among them, PROFIBUS-DP adopts the first layer, second layer and user interface in the OSI reference model. The user interface specifies the application functions that users, systems and different devices can call, and details the device behavior of various different PROFIBUS-DP devices; the physical layer transmission uses the RS485 standard. This structure ensures the real-time nature of communication and the low cost of system implementation. The protocol structure is shown in Figure 1. The PROFIBUS-DP system can be composed of the following three types of devices: (1) Level 1 DP Master Station (DPM1): The Level 1 DP Master Station is the central controller, which exchanges information with distributed stations (such as DP slave stations) within a predetermined information cycle. (2) Secondary DP Master Station (DPM2): The secondary DP master station is a programmer, configuration device or operation panel used in the configuration operation of the DP system to complete the system operation and monitoring purposes. (3) DP Slave Station: The DP slave station is a peripheral device for collecting and sending input and output information. Profibus-DP supports single master station or multi-master station systems. Tokens are transmitted between master stations and data is transmitted between master stations and slave stations, which provides high flexibility for system configuration. The master station obtains access rights by acquiring a token and can operate during the token holding period. It communicates with other master stations and slave stations according to the master-master and master-slave communication relationship table. Periodic data transmission between master stations and slave stations adopts a master-slave mode, where the master station sends or retrieves information from the slave station. In a single master station system, there is only one active master station during the operation phase of the bus system. The Profibus-DP data link layer provides the following transmission services: (1) Sending a message requiring acknowledgment (SRD service): Sending a message to a slave station to request acknowledgment. (2) Broadcast messages without acknowledgment (SND service): Sends a message to a group of slave stations to start the corresponding SDN service without requiring slave station acknowledgment. 1 Communication principle of PROFIBUS-DP In the PROFIBUS-DP system, user data transmission between DPM1 and related DP slave stations is automatically performed by DPM1 in a defined recursive order. When configuring the bus system, the user specifies the relationship between DP slave stations and DPM1, determining which DP slave stations are included in the information exchange cycle and which are excluded. Data transmission between DPM1 and DP slave stations is divided into three stages: parameter setting, configuration, and data exchange. In the parameter setting stage, each slave station compares its actual configuration data with the configuration data received from DPM1. Only when the actual data matches the required configuration data does the DP slave station enter the user data transmission stage. Therefore, the device type, data format, length, and number of inputs and outputs must be consistent with the actual configuration. In a practical system, to enable correct network communication between the master node and each slave node, the network must be configured, specifying the relationship between the master and slave nodes, determining which slave nodes are included in the information exchange cycle, and then downloading the network configuration information to the PROFIBUS-DP master station. PROFIBUS devices have different performance characteristics (different existing functions or possible different bus parameters), and these parameters vary for each device type and each manufacturer. To enable simple plug-and-play configuration of PROFIBUS, these characteristics need to be specified in the Device Database (GSD). GSD files are prepared by the manufacturers for each device type and provided to users in the form of a device database list. This file format facilitates the reading of device configuration information for any PROFIBUS DP device, automatically using this information when configuring the bus system; the system automatically checks and verifies data input errors and consistency related to the entire system. 2. Application Design of PROFIBUS-DP Communication in a Boiler System Taking a small boiler system as an example, a pure master-slave communication mode of PROFIBUS-DP is adopted. Five PROFIBUS-DP slave nodes are designed to monitor various controlled objects in the system: the first slave node controls and measures the boiler temperature, the second slave node measures the inlet flow rate, the third slave node controls and measures the liquid level in the furnace, the fourth slave node measures the jacket temperature, and the fifth slave node measures the outlet pressure. 2.1 System Hardware Configuration This system mainly consists of a master node (Class I master station) and field intelligent units (DP slave stations) forming a distributed network data monitoring system. The system structure diagram is shown in Figure 2. After the networking equipment completes the networking, the master and slave stations send or request data through the master station, and the slave stations respond to or confirm the data sent by the master station to complete the data transmission of the PROFIBUS network. 2.1.1 Master Node In this system, the master interface module uses the ANYBUS PROFIBUS-DP Master module from HMS, Sweden. This module is an embedded device. It possesses all the functions of a Class A master station, supporting communication baud rates from 9.6 kbit/s to 12 M bit/s, and can connect up to 124 slave stations. In hardware, it interfaces with the user CPU via 2K of dual-port RAM (DPRAM), which includes system information, hardware information, and handshake flags. Its I/O data transmission and request areas are both up to 512 bytes, and it can also allocate extended buffers. In software, it provides Mailbox Messages for information exchange with the user CPU. In this system, the master node monitors the entire system status through communication relationships established with the slave stations. The master node uses an ATMEL89C52 chip as its CPU, which, together with the PROFIBUS-DPMaster interface module, constitutes the PROFIBUS network master node, enabling the management of network nodes. The CPU and static memory exchange data with the dual-port RAM of the interface module via data lines, address lines, and control lines. The data content mainly includes process data, status information, and buffer configuration information of each slave node. An electrically erasable memory (EEPROM) with watchdog functionality is used to store the operating parameters of the master node, the networking information of the fieldbus network, and the node status information. Static RAM (RAM) is used as the data storage to store the process data of the slave nodes. The structure of the master node is shown in the upper half of Figure 2. 2.1.2 Field Intelligent Unit (DP Slave) In this system, the PROFIBUS-DP slave interface module uses the ANYBUS-SPROFIBUS-DP module from HMS, Sweden. Similar to the master module, it is also an embedded device. Hardware-wise, it interfaces with the user CPU through 2K dual-port RAM (DPRAM). The field intelligent unit uses a 51 series microcontroller as its core processor, mainly responsible for initializing the PROFIBUS slave module, including the allocation of I/O mapping areas—the allocation of mapping area addresses and the setting of lengths, and then implementing I/O data read and write operations according to the address allocation of the interface mapping area. The PROFIBUS slave interface module is embedded in the field intelligent unit, receiving control commands and providing various system parameters required by the master station. The structure of the field intelligent unit is shown in Figure 3. The field intelligent unit collects and processes the working parameters and status parameters of the controlled object, and writes information and data to the input mapping area of ​​the DP slave module for the master station node in the network to read and monitor by the host computer; at the same time, it reads the control information sent by the master station node from the output mapping area, and makes control decisions for the controlled object after judgment. 2.2 System Communication Network Construction There are two methods for network configuration: one is to complete it by writing message information to the master node; the other is to implement it through PROF IBUS-DP networking software. This system uses networking software for networking. As shown in Figure 4, the master module is connected to the PC through a connector, and the network configuration of the master module is performed directly. The networking software HMS SYCON provided by HMS in Sweden is specifically used for PROF IBUS-DP network configuration. It can configure master and slave stations, test network status, directly read the output and input data of master and slave stations, and set the bus data transmission rate, etc. In the system, there are 5 DP slave stations, and the size of the IN and OUT areas opened by each slave module is 20 bytes. During configuration, the IN and OUT areas of each Profibus slave station in the field are mapped one-to-one in SYCON according to their size, and all slave stations in the network are included in the information exchange cycle. An appropriate data communication baud rate is selected, and then the configuration information is downloaded to the master module. In this boiler system, the configuration of the data area in SYCON is shown in Table 1. The master module automatically sends or retrieves data to its assigned slave stations according to the downloaded information. If the configured data matches the actual data, the slave station enters the user data transmission stage, thus realizing data transmission between the Profibus-DP master and slave stations. It should be noted that when the network configuration is complete and the data is correctly mapped, the IN area of ​​the master module corresponds to the OUT area of ​​the slave module, and the OUT area of ​​the master module corresponds to the IN area of ​​the slave module. 3 Conclusion The debugging results show that all communication data is accurate and error-free, and the real-time performance reaches the millisecond level. The Profibus-DP network using SYCON has significant advantages: it does not require any external hardware, the method is flexible and universal, it can achieve offline networking, and the configuration adjustment is convenient. The large I/O mapping area of ​​the DP master and slave stations can fully meet the monitoring needs of the boiler. Following the method described in this paper, the network system constructed using PROFIBUS-DP is high-speed and inexpensive, making it particularly suitable for systems with high accuracy and real-time requirements, and has broad application prospects. References [1] Yang Xianhui. Fieldbus Technology and Its Application [M]. Beijing: Tsinghua University Press, 2000. [2] Xu Wenhui. Overview of Profibus-DP [J]. Aeronautical Electronics Technology, 2000, (1). [3] AnyBus Profibus-DP Master Fieldbus Manual [Z]. Doc.No.PDP-M-1.14 2002-06-15 HMS. [4] AnyBus Profibus-DP Fieldbus Appendix [Z]. Doc.No.ABS-PDP-1.32 2001.08-23 HMS. [5] PROFIBUS System Configurator [Z]. DOC.NO.HMS-SYCON-2.03 200 2-06-15 HMS.