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1 Communication master station DP interface circuit design Profibus field bus belongs to the master-slave polling mechanism, through the Profibus field bus to connect a series of master stations and slave station network nodes, using RS*485 balanced differential transmission and a shielded layer Twisted-pair cable for data transmission, to reduce the noise of industrial sites and to avoid the indirect level difference of multiple network nodes.
The physical layer includes coding types and transmission standards. The design of the hardware circuit is mainly the design of the interface circuit. Because the data link layer chip and the physical layer chip cannot be directly connected in the DP interface circuit design of the communication master station, an isolation circuit must be provided between the data link layer and the physical layer, and the bus over-current signal can also be prevented from making the data. The link layer chip is damaged. Domestic Profibus-DP communication master station uses 35Mbit/s bus transceiver (SN65ALS176D) to connect with 90Mbit/s single-channel digital isolator (ADUM1301CRW) to improve the anti-jamming ability of communication master's physical layer. Communication master interface circuit structure shown in Figure 1. 
2 software measures Profibus-DP field bus communication Master station software antijamming ability mainly refers to software fault tolerance. The data link layer is the core of the entire system. It establishes, maintains, and tears down link connections and implements error-free transmission. In order to make the DP communication master station program have higher anti-jamming capability, establish confirmation signals for the communication between the master station and the slave station; the communication master station communicates with the slave station through 3 kinds of state machines (SlaVe_Handler, Scheduler_Handler and Service_Handler). After the main program of the slave station stops running, it will start to process the interrupt service; after the master station receives the data frame, it calls the data management subprogram in the main program; after the communication master station completes the analysis and processing of the data, it calls The transmission program in the main program; the slave sends the response data or short reply to the master station. At this point, the Profibus-DP fieldbus communication master completed the processing of a message cycle (Figure 2).
In the process of data exchange between the master and slave stations, attention should be paid to the check sum of the packets sent by the user, that is, the sum of DA/SA/FC/DU (without carry). The master station checks the packet after receiving it. Once the checksum is incorrect, the master station will discard the packet.
3 Conclusion Based on the Profibus data transmission principle of the encoding and protocol analysis Profibus fieldbus communication master station anti-jamming capability, proposed in the data link layer and physical layer isolation circuit, the main station and the slave station to establish both sides of the confirmation signal Other hardware and software measures to mention their anti-jamming capabilities. The Profibus communication master station has been used in Huaneng Qinling Power Plant 2X660MW unit. Its stable and reliable operation meets the requirements of the power industry and Profibus fieldbus standards.
Research on Anti-interference Technology of Profibus-DP Communication Master Station
Profibus-DP communication master station anti-jamming technology research Profibus field bus protocol structure takes ISO/OSI as the reference model From bottom to top is simplified as physical layer, data link layer and application layer 3 layer. The physical layer (including the encoding mechanism) circuit and the data link layer (including the general structure description of the logarithmic protocol, security mechanism settings, etc.) are the key layers to guarantee the anti-interference ability of the Profibus communication master station. Profibus field bus carries on the data transmission between the master station and the slave station, all data transmission must carry on according to the certain code and the agreement carries on. Therefore, according to Profibus fieldbus data transmission principle, the coding and protocol are analyzed and studied respectively to improve the anti-interference ability of Profibus-DP master station.