The difference between PLC ladder diagram and structured programming language (SCL)

As we all know, programmable logic controllers (PLCs), hereinafter referred to as PLCs, are often used in electrical control. From various production equipment in the industrial field to various amusement equipment in amusement parks (such as roller coasters, carousels, etc.). In PLC programming, the most commonly used programming method by most PLC programmers is ladder diagrams (LAD), which is also a standard configuration of major PLC manufacturers. At the same time, Botu programming software under Siemens PLC in Germany launched another programming method comparable to ladder diagrams (LAD) very early: structured programming language (SCL).

The following is a brief analysis and comparison between Ladder Diagram (LAD) and Structured Programming Language (SCL). Please correct me if I find any shortcomings.

A ladder diagram (LAD) program consists of individual elements that can be connected in series or in parallel on a segment supply line. Most program elements must be provided with variables. At least one rung leads off the supply line. Segment programming begins at the left edge of the rung. The supply line can be extended by using multiple rungs and branches. For example, the following figure shows a ladder diagram (LAD) program:

1) Power line, 2) Ladder, 3) Branch, 4) Contact, 5) Coil, 6) Function box

The above is a basic introduction to ladder diagram (LAD)!

SCL structured control language is a high-level programming language based on PASCAL. The main elements in PLC control include: input, output, timer, memory bit and expressions, assignment operations, operators in high-level programming languages. In program control, it provides instructions such as creating program branches, loops or jumps. It is mainly used in: data management, process optimization, recipe management, mathematical calculation/statistical tasks.

In the SCL structured control language, the five most basic blocks are also particularly important components. For example: Organization block (OB): The organization block defines the structure of the user program.

Function Block (FC): A function contains a program routine for processing repetitive tasks. A function has no "memory".

Function Block (FB): A block of code that permanently stores values ​​in an instance data block so that the values ​​remain available even after the block has finished executing.

Instance data block: When an instance data block is called to store program data, the instance data block is assigned to a function block.

Global data block: A data area used to store data that can be used by any block.

Relatively speaking, we have talked a lot. Of course, the above content is by no means all. If you want to fully master the ladder diagram (LAD) and SCL structured control language