The Research Of Soft Plc Technology Based On Cortex-M3

Programmable Logic controller (PLC for short) has combined advantages of the relaycontroller such as low-in-price、easy-to-use and computers’general、flexible and powerful. Withhigh speed and high reliability, it is welcome in the field of industrial automatic control .But withthe rapid development of computer、network communication and microprocessor technology, theindustrial control process has become more and more complex, the technical requirements forcontrol is getting higher and its development is heading towards diversify and personalized. Thefixed hardware and closed program mode has prevented the development of PLC, in order toovercome these disadvantages of traditional PLC, and on the condition that the internationalprogramming standard IEC61131-3 been issued, soft PLC technology arises at the historic moment.It has greatly promoted the development of PLC towards general and open.By study the soft PLC technology at home and abroad, this project has designed the algorithmsthat used to convert the ladder diagram into standard C language. We chose STM32 which useCortex-M3 for the kernel as the processor of our hardware platform, by compiling the C object codethat the ladder program generated and the low level drivers, and then run them on the hardwareplatform, we realized the basic function of the PLC. Now, almost all of the MCU and ARMprocessor in the market can support C language, so when we want to transplant the ladder programto other platforms to use, we just need to modify a small amount of drivers. According to the factorssuch as hardware demand、cost and so on, the choose of the processor is flexible. The main work ofthis project are as following:1.Introduced the system structure and working principle of the traditional and soft PLC,analyzed the demand of this system and then determined the specific function of each module.2.Designed and realized the interface of this system, provided a good and humanizedprogramming environment for users.3.Introduced the function of the elements, analyzed the complex relation of the branches, anddesigned corresponding data structures for the elements、parallel nodes、series node s and rungs onthis basis.4.Designed and realized the algorithm for specific edit operation ,such as element find、elementadd and so on.5.Designed a kind of intermediate language, and converted the ladder program to it. Thisintermediate language can not only directly convert into C language, but also can convert into otheradvanced programming languages such as C++. It provided good interfaces for system’s subsequent optimization and function expansion.6.Translated the intermediate language into the standard C language, and programmed the lowlevel drivers.7.Designed a small drip irrigation system, validated the function of hardware and softwareplatforms of this system comprehensively.