Research And Realization Of Ethernet Interface For Field Devices

With the development of the Industrial Ethernet technology, Ethernet has already permeated through control layer and device layer. So far, almost all main providers of PLC and remote I/O devices can provide products with Ethernet interface. It can be predicted that there will be no market for the products without Ethernet interface in the future. So many field supervisory control devices developed before need to be appended Ethernet interface urgently. The main task of the paper is to research the realization method of linking field supervisory control devices to Ethernet with low cost by experiment. The main contents are as follows. 1. The paper presents the global design scheme and considers the design frame, thought and method of the hardware and software in terms of the overall situation. 2. Using 51 serial MCU and the Ethernet controller RTL8019AS, the paper establishes the experimental platform with simple interface circuit, small volume and low cost. The paper also designs the Ethernet controller's driver according to its operating principle. 3. The paper designs the embedded TCP/IP stack and offers the simple, convenient and practical API(Application Programming Interface). On the basis of guaranteeing to realize the main function of TCP/IP, the paper simplifies the protocol of TCP/IP, reduces the program code and saves the memory space taken up. The embedded TCP/IP stack has the following features: (1) It supports multi TCP connections and multi UDP ports. (2) The API is simple and convenient to be used and easy to be understood. (3) The size of its code and the RAM it uses is moderate. (4) The code is easy to be migrated and cut. (5) The program is easy to be read and maintained. 4. By calling the API functions, the system test of the embedded TCP/IP is performed. The test indicates that the experimental provision has realized the main function of every layer of TCP/IP, has high performance and can be applied to industrial field.