The software programming language of PLC has distinct characteristics compared to general computer languages. It is different from both high-level languages and general assembly languages, and it must meet the requirements of being easy to write and debug.
Early PLCs only supported ladder diagram programming language and instruction list programming language. Now, according to the International Electrotechnical Commission, five languages that can support PLC programming have been established. Today, I will briefly talk about these languages, their characteristics and applications.
Table of contents
I. Ladder Diagram Delete (LD)
II. Command List: Delete (IL)
III. Functional Module Diagram: Delete (FBD)
IV. Sequential Function Chart (Delete, SFC)
V. Structured Text Delete (ST)
I. Ladder Diagram Delete (LD)
Ladder diagram language is the most commonly used programming language in PLC programming. It is a programming language similar to that used for relay circuits. Because electrical professionals are more familiar with relay control, ladder diagram programming language is widely used.
Features:
1. It is intuitive, visual, and practical, and corresponds to the electrical operation schematic diagram.
2. Ladder diagram programming is similar to relay control systems, making it easy for electrical professionals to learn.
3. The relays used in ladder diagrams are implemented using soft components, making them more flexible and convenient to use and modify.
II. Command List: Delete (IL)
Instruction list programming languages are mnemonic programming languages similar to assembly languages, consisting of opcodes and operands, just like assembly languages.
Features:
1. Mnemonics are often used to represent operational functions, making them easy to remember and master.
2. It corresponds to ladder diagrams and can be converted to each other in PLC programming software. Some software does not have this function (such as Mitsubishi's GXWorks2).
3. Easy to operate: The handheld programmer uses mnemonic symbols on its keyboard, allowing programming and design to be performed even without a computer.
III. Functional Module Diagram: Delete (FBD)
Function block diagram language is a PLC programming language similar to digital logic circuits, and it is relatively easy for people with a background in digital circuits to master.
Features:
1. Analyzing and understanding the control scheme by functional modules is simple and easy.
2. Functional modules express functions in a graphical form, which is highly intuitive and easy to operate.
3. For large-scale applications, the functional module diagram clearly expresses the functional relationships, greatly reducing programming, configuration, and debugging time.
IV. Sequential Function Chart (Delete, SFC)
Sequential Function Chart (SFC) is a programming language designed to meet the requirements of sequential logic control. It features a graphical representation, enabling relatively simple and clear description of all phenomena in concurrent and complex systems. It allows for direct programming based on models, and therefore has gained widespread application.
Features:
1. Organized by function, the program is arranged in a logical and clear manner, facilitating user understanding of the program.
2. For large programs, the design can be divided into tasks, and a more flexible program structure can be adopted, which can save program design and debugging time.
ST)
Structured text programming (SMT) is a programming language that uses structured descriptive text to describe programs. It is similar to a high-level programming language. In large and medium-sized PLC systems, structured text is often used to describe the relationships between various variables in the control system to accomplish the required functions or operations.
Features:
1. Using a high-level programming language allows for the completion of relatively complex control operations.
2. Higher requirements; requires knowledge of high-level computer languages and programming skills.
3. Due to its poor intuitiveness and operability, it is often used for user program development that is difficult to implement in other programming languages.
In PLC control system design, different PLC programming software models support different types of the above five programming languages. Therefore, in addition to understanding the hardware performance of the PLC, it is also necessary to understand the types of programming languages supported by the PLC.
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