Understanding Function Blocks in Siemens PLC: A Comprehensive Guide

Key Takeaways

What is a function block in Siemens PLC?A block of code that performs specific functions, with parameters stored in a data block for future use.
Why use function blocks?They enhance efficiency, consistency, and simplify troubleshooting by reusing the same code across projects.
How to create a function block?Using Siemens TIA Portal, add a new block, define parameters, and program the logic.
Examples of usePump systems, conveyor belts, motor control, and VFD integration.
Benefits of function blocksReusability, efficiency, consistency, easier maintenance, and troubleshooting.


In the world of industrial automation, Siemens PLCs stand out for their reliability and advanced capabilities. A key feature that enhances the functionality and efficiency of Siemens PLCs is the use of function blocks. But what exactly are function blocks, and why are they so important?

What is a Function Block?

A function block (FB) in Siemens PLC programming is a modular block of code designed to perform specific functions. Unlike a simple function call (FC), a function block retains its input, output, and in-out parameters in an associated data block (DB). This memory retention allows the function block to use these parameters in future executions, making it highly useful for tasks that require consistent state information.

Comparison with Function Calls

Function blocks differ from function calls in that function blocks store data persistently, while function calls do not. This makes function blocks suitable for applications where the state or historical data needs to be retained across different executions of the block.

Creating Function Blocks in Siemens PLC

Step-by-Step Guide

  1. Opening TIA Portal: Begin by opening the Siemens TIA Portal, the integrated automation environment for PLC programming.
  2. Adding a New Block: Navigate to the project tree, right-click on “Program Blocks,” and select “Add New Block.” Choose “Function Block” and give it a meaningful name.
  3. Naming and Setting Parameters: Define the input, output, and in-out parameters for the function block. These parameters will be stored in the associated data block.
  4. Programming the Logic: Implement the desired logic within the function block. Use standard programming constructs and PLC-specific instructions to define the behavior of the block.

Example Application: Pump System

To illustrate the creation and use of a function block, let’s consider a practical example: programming a function block for a pump system.

  • Logic Implementation: The function block, named “Pump_Standard,” will include the necessary logic for controlling a pump, such as starting, stopping, and handling alarms.
  • Inserting into Organizational Block: Once the logic is implemented, the function block can be inserted into an organizational block (OB1) for execution. This involves connecting the local inputs and outputs to real-world inputs and connections.

Practical Applications of Function Blocks

Function blocks can be used in various industrial applications to simplify programming and enhance functionality.

Industrial Examples

  • Conveyor Systems: Function blocks can manage multiple conveyor belts efficiently. Each conveyor can have its function block instance, retaining specific state information and control logic.
  • Motor Control: Function blocks can control motor systems, handling tasks like starting, stopping, speed control, and fault management.
  • VFD Integration: Variable Frequency Drives (VFDs) can be integrated with PLCs using function blocks to manage their parameters, alarms, and data exchange.

Benefits of Using Function Blocks

Using function blocks in Siemens PLC programming offers several benefits:

  • Efficiency and Consistency: Function blocks streamline programming by allowing the reuse of the same logic across different projects, ensuring consistency and reducing programming effort.
  • Reusability: Once created, a function block can be reused in various parts of a program or across multiple projects, saving time and effort.
  • Troubleshooting and Maintenance: Function blocks make it easier to troubleshoot and maintain the system. Changes made to a function block are automatically reflected wherever the block is used, simplifying updates and modifications.

By leveraging function blocks, you can enhance the efficiency, consistency, and maintainability of your Siemens PLC programs, making them a powerful tool in industrial automation.

For more detailed guides on Siemens PLC programming, visit our comprehensive guide to connecting your Siemens PLC with an HMI or our ultimate guide to buying Siemens PLCs.

Expert Tips and Best Practices

Using function blocks effectively can greatly enhance the performance and maintainability of your Siemens PLC programs. Here are some expert tips and best practices to consider:

Programming Tips

  1. Modularity: Break down complex processes into smaller, manageable function blocks. This modular approach simplifies programming and troubleshooting.
  2. Consistent Naming Conventions: Use clear and consistent naming conventions for your function blocks and parameters. This practice improves readability and maintainability.
  3. Documentation: Document your function blocks thoroughly. Include descriptions of their purpose, inputs, outputs, and internal logic. Well-documented code is easier to understand and modify.
  4. Testing: Test function blocks individually before integrating them into the main program. This step helps identify and resolve issues early.

Memory Management

  1. Efficient Use of Data Blocks: Ensure that data blocks associated with function blocks are used efficiently. Avoid unnecessary data storage to optimize memory usage.
  2. Static vs. Temporary Data: Use static data for parameters that need to be retained across executions. Use temporary data for variables that do not require persistent storage.

Common Pitfalls

  1. Overcomplicating Logic: Keep the logic within function blocks as simple as possible. Overcomplicated logic can be difficult to debug and maintain.
  2. Ignoring Reusability: Design function blocks with reusability in mind. Avoid hardcoding specific values or parameters that limit the block’s applicability to other projects.

By following these tips and best practices, you can maximize the benefits of using function blocks in your Siemens PLC programming projects.


Function blocks are a powerful feature of Siemens PLC programming that can significantly enhance efficiency, consistency, and maintainability. By understanding how to create and use function blocks effectively, you can streamline your programming process and ensure the reliable operation of your automated systems.

Summary of Benefits

  • Efficiency: Reduce programming time and effort by reusing function blocks.
  • Consistency: Ensure consistent functionality across different parts of a program or multiple projects.
  • Maintenance: Simplify troubleshooting and updates by centralizing logic within function blocks.

Future Applications

As industrial automation continues to evolve, the use of function blocks will become even more critical. Future applications may include more advanced control systems, integration with IoT devices, and enhanced data analytics capabilities. Staying up-to-date with the latest developments in PLC programming and function block technology will be essential for maintaining a competitive edge.

For more detailed guides and expert insights on Siemens PLC programming, explore our blog and discover a wealth of resources designed to help you master the art of industrial automation.

Additional Resources


What is a function block in Siemens PLC?

A function block is a modular block of code that performs specific functions and retains its parameters in an associated data block for future use.

Why use function blocks instead of function calls?

Function blocks store data persistently, making them suitable for tasks that require consistent state information across different executions.

How do I create a function block in Siemens TIA Portal?

To create a function block, navigate to the project tree, add a new block, define the parameters, and program the logic within the block.

Can function blocks be reused?

Yes, function blocks are designed to be reusable, allowing you to apply the same logic across different projects or parts of a program.

By leveraging the power of function blocks, you can enhance the efficiency, consistency, and maintainability of your Siemens PLC programs, making them an invaluable tool in industrial automation.


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