Open Programmable Control System

As a kind of important basic equipment in automation industry, PLC plays more and more important role in the field of industry manufacture. However, key technologies of high-end PLC, which processes communication, CNC, data acquisition functions, have been held by foreign such as USA's, European Union's and Japanese enterprises for a long time. These enterprises monopolize Chinese market for all these years. In addition, their sale price is very high and they are not open to consumers. So it is very hard to be widely used. In a word, it is very necessary to develop a new PLC which property right owned by ourselves. Recently, the development of high-performance single chip has made it possible for us to develop PLC in hardware. To develop an exoteric, module and low price PLC is one direction that domestic enterprise should work on.Under these conditions, we summarized the basic structure, principle and features of PLC, constructed structure model of exoteric PLC and selected 51 kernel single chip STC89C51 as the processor of the PLC. After that, we designed and made a mini PLC. This PLC has the function of logic input, logic output and communication. On that basis we researched on the instruction set of 51 single chip and FX2N PLC, set scheme of PLC integrated developement system on C51, and designed the PC software at the use of C++Builder. The software has the functions of editing ladder diagram, doing logical operation, processing data and so on. It also can compile the ladder diagram to the excuteable file which could be excuted by 51 single-chip's CPU.In the thesis, the hardware system of the PLC was analyzed in detail, as well as the achievement of the ladder diagram. We also described how to translate the instruction set of PLC through the complier. Furthermore, we researched on the data format about C51 compile system, discussed the method how to use the C51 complier, linker and converter. At last, it makes it successful in converting the ladder language to machine language. At the end of the thesis, we analyzed the communication principle and structure of the USB. After that, we programmed the fireware and finished the data communication test. As a result, we succeed in applying the USB communication in the PLC field.