The Research Of Coding And Resolving Of PLC LD Based On Standard IEC61131-3

IEC61131-3 is the first international standard which provides standardized program language for industrial automatic control system. This standard plays an important role on the development of the software technique of programmable controller, even on the development of the software technique of whole industrial control. There will be no solid base of today's opening system of PLC without the standardization of program language. As LD is often used as program language of PLC, this paper uses LD as the main program language to develop PLC according with the standard IEC61131-3.The paper begins by introducing the proposal, the development and the actuality of PLC and the origin of the standard IEC61131-3. Subsequently, the software model, communication model and common elements are presented, for shadowing the in-depth research to follow.Next, on the basis of research of the standard IEC61131-3, a software structure of PLC software system is proposed and to be explained by the running result of program. Then the paper discusses the configuration elements of PLC software system, especially focusing on the related setting of configuration and resource and on task system and access path of PLC. This establishes the basis for the design of PLC. Last, based on the combination of the functions of traditional PLC and the standard IEC61131-3, the paper proposes all designed functions and function blocks.Thereafter, this paper designs the first-class code and the second-class code of LD language of PLC software system, and elaborates their definitions and structures. As the second-class code needs to be downloaded to PLC, the downloading format of the second-class code is designed. The paper also designs the resolving arithmetic of LD language of PLC software system which is used to transform the first-class code to the second-class code, and an example is presented to explain and validate the arithmetic of coding and resolving.Finally, the whole designed PLC software system is described detailedly to give readers a more clear understanding of this paper. Then upon summarizing the research results and deficiencies, the prospect of PLC based on the standard IEC61131-3 is elaborated.The innovations of this paper are the designings of first-class code and second-class code and the designing of the resolving arithmetic which is used to transform the first-class code to the second-class code. The designing of first-class code mainly bases on the display of LD and the confirmation of correlation of elements of LD. The designing of second-class code accordings to the IL of PLC traditional program languages. And the paper proposes a new form of instructions. The desinging of the resolving arithmetic bases on method of ratiocination, and it proves that the arithmetic is accurate. First, the arithmetic resolves some simple LD networks. Then a complex LD network which is composed of the simple instances can be resolved by the arithmetic accurately.The research of PLC software of this paper is very important to the designing of PLC based on The Standard IEC61131-3.