As a world-famous enterprise, Mitsubishi Electric automation PLC has a very high market share in China. As far as the programming language is concerned, it currently supports the mainstream programming methods in the market, such as ladder diagram, St, SFC and FBD. In terms of the current usage habits of Asians, ladder diagram is the main, FBD and St are also more, and different programming types are selected according to their preferences.
There is no best programming language, only more suitable! The programming languages of Mitsubishi PLC include instruction table, ladder diagram, step SFC, structured text st and structured ladder diagram FBD. Each programming language has its own characteristics and corresponding application occasions. The selection of programming language is generally related to the model of PLC (Q, l, FX Series), project type (simple project, structured project) and relevant contents of control (sequence control, process control and communication control).
Mitsubishi PLC programming language has the following characteristics:
1. Instruction structure in graphical form: the program is expressed in graphical form, and the instructions are composed of different graphical symbols, which is easy to understand and remember. In the logic operation part, almost all manufacturers adopt ladder diagram similar to relay control circuit, which is easy to accept. More complex arithmetic operations and timing counting are generally represented with reference to ladder diagram or logic element diagram. Although they are not as symbolic as logic operations, they are also popular with users.
2. Simplify the generation process of application software: write programs in assembly language and high-level language, and complete the three processes of editing, compiling and connecting.
3. Simplified program structure: the program structure of Mitsubishi PLC is usually very simple, typically block structure. Different blocks complete different functions, so that the program debugger has a clear concept of the control function and control sequence of the whole program.
4.。 Explicit variable constant: the graphic symbol is equivalent to the operation code, which specifies the operation function, and the operands are filled in by the user, such as k400, T120, etc. The variables and constants in Mitsubishi PLC and their value range are clearly specified, which is determined by the product model. You can refer to the product catalogue manual.
5. Strengthen debugging means: whether it is assembly program or high-level language program debugging, it is a headache for editors. The program debugging of Mitsubishi PLC provides complete conditions. Using the programmer, using the keys, display and internal editing, debugging and monitoring on Mitsubishi PLC and programmer, and with the support of software, the diagnosis and debugging operation are very simple.
Let’s first introduce the characteristics of Mitsubishi programming language:
[instruction table] the way of inputting sequence control instructions through “LD”, “and”, “out” and other instruction languages is the most basic input form in sequence control program.
[ladder diagram] use sequence symbols and software component numbers to draw sequence control ladder diagram on the picture shown in the figure, so that it can be better understood and mastered in the form of contacts and coils. It is very suitable for PLC beginners and personnel with electrician foundation.
[SFC] completes the programming according to the design sequence of mechanical action process, which is suitable for the programming of mechanical action equipment.
[st structure text] a program language with syntax structure and text form similar to C language. Conditional statements can be used to select branches and repeat with circular statements. The program editing is very concise and clear, which is suitable for personnel with computer foundation.
[structured ladder diagram] it can use circuit symbols such as contacts, coils, functions and functional modules to describe the program in the form of graphics, which is easy to understand intuitively. Therefore, it is widely used in sequence control program.
According to the project type, the simple project generally adopts three languages: instruction table, ladder diagram and SFC. Among them, ladder diagram is widely used, and the structured project can adopt ladder diagram, St, SFC and FBD.
1. Select according to the type of PLC. Small computers such as FX series mainly use ladder diagram language for programming. It belongs to integrated PLC, which is integrated with CPU, power supply, IO module and communication module. It is suitable for small-scale production. Medium and large computers are modular, such as IO, communication and positioning modules. The processing of each module part is relatively clear, and the programming is completed for the module. The part program can be saved as a library, which helps to improve the reusability of the program. Therefore, it is mostly completed by using structured programming language. In the past, when programming with simple ladder diagram language, there is no clear interval between all processes. In complex step programs, it is sometimes necessary to check and correct from beginning to end. Therefore, it is necessary to realize efficient programming, standardize and share commonly used programs, and reduce the man hours required for new development.
2. Engineering type, that is, the simple and structured program mentioned above. If we want to control less content, single function and less complex logic, we can choose simple engineering and complete it by using instruction table, ladder diagram and SFC. If it is a large-scale process control or distributed network control with many control objects, it needs to adopt structured programming to shorten the programming time and reduce the time of redistribution of software components through reuse. The most important difference between simplification and structure is the use of “tags”.
3. Control content: three control contents of PLC: 1 sequence control, the most basic logic control, 2 process control is mainly for analog quantity, 3 communication control is mainly related to data processing, network, etc. The complexity is also increasing, and the ladder diagram is somewhat stretched when dealing with these, such as string, database, network and other data processing, which requires a large number of steps to complete. With the complexity of processing content, memory capacity and processing speed will be affected. Therefore, in the face of complex control content, it is necessary to adopt efficient programming languages, such as structured text st, structured ladder diagram module and FBD.