The Design And Implementation Of The Soft PLC Based On Linux Operating System

The soft PLC technology has become one of hot spots in the world because it overcomes the shortcomings of traditional PLC such as poor openness and poor extendibility. The defects of the soft PLC based on PC are obvious, for example, the high cost and poor suitability. With the rapid development of embedded technology, soft PLC combined with embedded technology solves the above problems and has been a new trend.The structure and principle of the soft PLC system were put forward, and the key technologies and standards related to the soft PLC design were introduced. Soft PLC system can be divided into two parts, development system and running system. The design and implementation of operation system were studied in detail. In this paper, the soft PLC running system was designed based on the embedded hardware platform with PowerPC processor of Freescale, which improved the real-time and stability of the system. Besides, the Linux operating system controlled development cost and improved the flexibility of system development.Cross-platform design was adopted to ensure the smooth transplant between different operating system for application software. In addition, the modular and hierarchical design eliminated the correlation between different levels, which facilitated the upgrading and maintenance of products. The concept of virtual machine running system was put forward to enhance the openness of the system. The virtual machine software realization of the operation system was expounded, mainly including the main running program of virtual machine and the basic logic instructions. Besides, the problem of communication between the development system and running system was studied. A proprietary protocol was set based on TCP/IP protocol. This protocol adopted the sliding window mechanism and solved the problem of the file transfer efficiency and flow control, so as to improve the control efficiency of the soft PLC system.Finally, the system function was verified through a test of an LED control model, and stability and openness was also proved.