Jun 8, 2023

PLC Programming Languages

In summary, PLC programming languages are basically of two types: Textual languages and Graphical languages. There are 5 programming languages under those categories:

1. Structured Text (ST)
2. Instruction List (IL)
3. Ladder Diagram (LD)
4. Function Block Diagram (FBD)
5. Sequential Function Chart (SFC) 

The first 2 are Textual languages and the other 3 are Graphical languages.

Now, let's discuss the above PLC programming languages in detail.

PLC Programming Languages


If you've ever wondered how complex industrial processes are automated, the answer lies in Programmable Logic Controllers (PLCs). These robust electronic devices have revolutionized industries by providing a reliable and efficient means of controlling machinery and processes. 

At the heart of PLC programming lies a range of specialized programming languages that enable engineers and technicians to communicate with these powerful controllers. 

In this article, we'll explore different types of PLC programming languages, their significance, and how to choose the right one for your automation needs.

What is a PLC?

A Programmable Logic Controller (PLC) is a digital computer used to control and automate industrial processes. PLCs are widely used in manufacturing plants, power stations, water treatment facilities, and various other applications that require precise control and monitoring. 

These devices are designed to withstand harsh environments, making them ideal for industrial automation.

Importance of PLC Programming Languages

PLC programming languages serve as the interface between human operators and the PLC hardware. 

They allow engineers to develop logic programs that dictate the behavior of the PLC. The choice of programming language directly impacts the automation system's efficiency, readability, and maintainability. 

It is crucial to select the appropriate programming language based on the specific application requirements and the skillset of the programmer.

5 Common PLC Programming Languages

1. Structured Text (ST)

Structured Text (ST) is a high-level programming language that resembles Pascal or C programming. It allows for complex calculations, data manipulation, and advanced control algorithms. 

ST is often preferred for applications requiring extensive mathematical computations or complex data structures.

2. Instruction List (IL)

Instruction List (IL) is a low-level programming language that resembles assembly language. 

It provides direct control over the PLC's internal operations and is often used in performance-critical applications or when optimizing code execution speed is crucial.

3. Ladder Logic

Ladder Logic is the most widely used programming language in the world of PLCs. It derives its name from the ladder-like diagram representation, resembling electrical relay circuits. 

Ladder Logic is intuitive and easy to understand, making it an excellent choice for beginners. It is particularly suitable for discrete control applications.

4. Function Block Diagram (FBD)

Function Block Diagram (FBD) is a graphical programming language that uses interconnected blocks to represent functions and operations. 

It is ideal for visualizing complex control systems and is often used in applications with multiple parallel processes.

5. Sequential Function Chart (SFC)

Sequential Function Chart (SFC) is a graphical programming language that enables the description of sequential processes. 

It is particularly suitable for applications with complex sequences of operations or state-based control systems.


Advantages and Disadvantages of Different PLC Programming Languages

Let's examine the pros and cons of the most commonly used PLC programming languages:

Structured Text (ST)


- Supports complex calculations and data manipulation.
- Resembles high-level programming languages.
- Ideal for applications with advanced control algorithms.


- Steeper learning curve for beginners.
- Requires a good understanding of programming concepts.

Instruction List (IL)


- Provides direct control over the PLC's internal operations.
- Optimizes code execution speed.
- Suitable for performance-critical applications.


- Difficult to read and understand.
- Limited readability and maintainability.

Ladder Logic


- Easy to understand and learn.
- Graphical representation resembles electrical circuits.
- Well-suited for discrete control applications.


- Limited capabilities for complex calculations.
- Not suitable for handling large amounts of data.

Function Block Diagram (FBD)


- Visual representation of interconnected blocks simplifies complex control systems.
- Easy to understand and modify.
- Suitable for applications with parallel processes.


- Limited availability of FBD programming resources.
- May not be the best choice for small-scale applications.

Sequential Function Chart (SFC)


- Enables graphical representation of sequential processes.
- Supports state-based control systems.
- Easy to visualize complex control sequences.


- Not suitable for all types of control applications.
- Requires careful design to avoid excessive complexity.

Choosing the Right PLC Programming Language

When selecting a PLC programming language, several factors should be considered:

Application Requirements

The nature of the automation application plays a vital role in determining the suitable programming language. 

For example, discrete control applications are well-suited for Ladder Logic, while complex calculations may require Structured Text (ST).

Programmer's Skillset

The expertise of the programmer should be taken into account. If the programmer is proficient in a particular programming language, it may be more efficient to use that language for development and troubleshooting.

Industry Standards

In some industries, specific programming languages may be favored due to standardization or compatibility reasons. It is essential to consider industry guidelines and regulations when choosing a PLC programming language.


PLC programming languages form the backbone of automation systems, enabling precise control over industrial processes. By understanding the characteristics and advantages of different programming languages, you can make informed decisions when developing automation solutions. 


FAQ 1: Can I use multiple programming languages in the same PLC?

Yes, some PLCs support multiple programming languages. This can be useful when different parts of an application require specific language features or when integrating existing code written in different languages.

FAQ 2: Is there any free PLC programming software available?

Yes, some manufacturers offer free versions of their PLC programming software, allowing users to practice and develop programs without the need for expensive licenses. However, advanced features may be limited in the free versions.

FAQ 3: Can I convert programs written in one language to another?

In some cases, it is possible to convert programs between PLC programming languages using software tools or manual rewriting. However, the level of automation and ease of conversion may vary depending on the complexity and structure of the original program.

FAQ 4: Which programming language is best for beginners?

Ladder Logic is often recommended for beginners due to its graphical representation and simplicity. However, it is essential to consider the specific application requirements and industry standards when choosing a programming language.

FAQ 5: How can I keep up with the latest trends in PLC programming languages?

To stay updated with the latest trends in PLC programming languages, follow industry publications, attend conferences and webinars, and engage in online communities dedicated to automation and PLC programming. 

Regularly exploring the manufacturer's resources and software updates can also provide insights into new features and capabilities.

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