Siemens PLC programming language - Solutions - Huaqiang Electronic Network

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Different businesses have different programming languages ​​for plc, but for a certain business, PLC programming languages ​​are just a few. Below, take the programming language of Siemens PLC as an example to illustrate the similarities and differences of various programming languages.

1. Sequential function chart (SFC-SeauentialFuctionChart)

This is a graphical language on top of other programming languages ​​for programming sequential control programs (eg, robotic control programs). At the time of writing, the process is divided into several sequential steps, each of which includes the action of controlling the output, and the conversion from one step to the other is controlled by the conversion conditions, and is particularly suitable for the manufacturing process.

The programming language in Siemens STEP7 is S7 Graph.

2, ladder diagram (LAD-LAdderDiagram)

This is the most used PLC programming language. Because it is very similar to the relay circuit, it is easy to understand by the electrical personnel familiar with the relay control, and is especially suitable for digital logic control.

The ladder diagram consists of contacts, coils, and instructions represented by squares. The contacts represent logic input conditions, the coils represent logical operation results, commonly used to control the indicator lights, switches and internal flags. The instruction box is used to indicate additional instructions such as timers, counters, or math operations.

In the program, the leftmost is the main signal flow, and the signal flow always flows from left to right.

Not suitable for writing large control programs.

3, statement table (STL-STatementList)

It is a text programming language similar to microcomputer assembly language. It consists of multiple statements and a program segment. The language table is suitable for experienced programmers and can implement functions that some ladder diagrams cannot.

4, function block diagram (FBD-FunctionBlockDiagram)

Function block diagrams use graphical logic symbols similar to Boolean algebra to represent control logic. Some complex functions are represented by instruction blocks and are suitable for programmers with digital circuit foundations. The function block diagram uses a block diagram similar to the AND gate or OR gate to represent the logical operation relationship. The left side of the box is the input variable of the logic operation, the right side is the output variable, and the small circle at the input and output ends indicates the "non" operation. The frames are connected together by "wires" and the signals are from left to right.

5, structured text (ST-StructuredText)

Structured Text (ST) is a specialized high-level programming language created for the IEC61131-3 standard. Compared to ladder diagrams, it implements complex mathematical operations, and the programs written are very simple and compact.

STEP7's S7SCL structured control language, programming structure and C language and Pascal language are similar, especially suitable for people accustomed to programming with high-level language.