Development Of A SoftPLC System Based On RTLinux

This project is part of "Development and Application of Open Architecture Software CNC System" which is supported by Sichuan Province Key Research and Development (Grant No. 03GG006-013-1).PLC technology is playing a very important role in the manufacturing automation filed. However, traditional PLC system has many disadvantages, such as in open, modular, scaleable, economical, reliable and maintainable. The key cause of the disadvantages is that traditional PLC system is developed based on proprietary hardware and software. With the development of OMAC and IEC1131-3 standard, realizing PLC based on "de facto" standards and commercial hardware and software is becoming a stream.At the present time, many end user companies have selected Microsoft operating systems as the baseline infrastructure for their control, operator interface, and information technology systems. The key driver behind this selection is the dominant acceptance of Microsoft technologies in the computing and information technology markets. However, Microsoft Windows is not a real time operating system, and the real time extensions of Windows such as RTX, InTime and LP-Win are expensive. RTLinux is a real time operating system with excellence performance. It can be use accomplish real time multi-tasks scheduling without secondary CPU. Its source code is open for end user. Therefore, developing and open SoftPLC system based on RTLinux helps to improve the performance of PLC system. The paper addresses the implementation of an open SoftPLC system based on RTLinux.The software consists of No-real time layer developing system and real time layer running system. Developing system is composed of editor, compiler anddebugger, which be developed in Linux user space. Running system is composed of scanner and driver, which be developed in RTLinux real time kernel space. The details of the software are presented.Based on the research of SoftPLC system, the concepts of programming element, ladder level and class ladder are put forwarded. The details of the data structure of each other are discussed. The algorithms for calculating class ladder, and editing class ladder are given in detail.The software prototype has been built initially and verified the practicability of the theory model. By the system, designers can express their program with Ladder Diagram, can edit, compile, debug, can do fundamental logical calculation such as "AND", "OR", "NOT", "SET" and "RESET" and so on.At present, the prototype system is just completed in the main, so there is still much work to be done in the further development.