PLC software

PLC software consists of system program and user program. System program written by PLC manufacturers design, and in the PLC system memory, the user cannot directly read and write with the change. System program generally includes diagnostic procedures, input processing program, the compiler, the information transmission, monitoring program, etc. The PLC user program is the user's use of PLC programming language, the program according to the control requirement. In the application of PLC, the most important thing is to use PLC programming language to write the user program, in order to realize the control aim. Because PLC is developed specifically for industrial control device, its main users are the general electrical technicians, and master the ability to meet their traditional customs, PLC programming language used primarily than computer language is relatively simple, and easy to understand, image of special-purpose language. PLC programming languages are varied for different manufacturers, different series of PLC products adopt the programming language expression way is different, but basically can be summarized two types: one is to use character expression of programming languages, such as the statement table, etc. ; The second is to use graphic symbol expression programming language, such as ladder diagram. Following a brief introduction to several common PLC programming language. 1. Ladder diagram language ladder diagram language is commonly used in the traditional electric control system of the contactor, relays and other graphic expression has evolved on the basis of symbols. It is similar to electric control circuit diagram, inherited the traditional electrical control logic used in frame structure, logic operation way and the form of input and output, has the characteristics of the image, intuitive, practical. Therefore, this kind of programming language for the general electrical technical personnel, is the most widely used PLC controller programming language, is the first of its kind in the PLC programming language. As shown in figure 1 is the traditional electrical control circuit diagram and PLC ladder diagram. Figure 1 electric control circuit diagram and ladder diagram a) The electric control circuit diagram b) PLC ladder diagram can be seen from the picture, two kinds of basic graph represent thought is consistent, the specific expression has a certain difference. PLC ladder diagram using the internal relay, timer/counter, etc. , are all realized by software, easy to use, flexible modification, is the original electric control line hard wiring. 2. Statements table this programming language is a kind of similar mnemonics to assembly language programming. Usually used in the applications of PLC, simple programming, the programmer no CRT screen display, or no larger LCD screen display. Therefore, use of a series of PLC operation command statements table described ladder diagram, and then through a simple programmer input to the PLC. Although each PLC controller manufacturer statement table form is not the same, but the basic functions. The following is a ladder diagram in figure 1 and the corresponding ( FX series PLC) Statements table procedures. Step number order data 0 LD X1 1 OR 2 Y0 ANI X2 3 OUT Y0 4 LD X3 5 OUT Y1, statement which is the basic unit of the table program, each statement as well as microcomputer by address ( Step number) , operation code ( Instructions) And the operands ( Data) Of three parts. 3. Logic diagram language logic diagram is similar to the digital logic circuit structure of the programming language, and gate, or gate, not gate, timer, counter, the trigger logic symbols, etc. A digital circuit basis electrical technician is easy to grasp, as shown in figure 2. Figure 2 4 logic diagram programming language. Function table figure language function chart ( SFC language) Is a relatively new programming method, also known as the state transition diagram language. It will be a complete control process is divided into several stages, each stage has different actions, has the certain transformation between the phase condition, transition conditions meet the implementation phase transfer, on the one stage movement ended, the next stage action began. Is to use function table figure expression of a process control, is especially for sequential control system. 5. High-level language with the development of PLC technology, in order to enhance operation, data processing and communication function of PLC and programming language cannot meet these requirements. PLC is carried out in recent years, especially the large PLC, can be a high-level language, such as BASIC language, C language, C + + programming. After using a high-level language, users can like using common microcomputer PLC operation, make the various function of the PLC controller into better play.
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