How do I add a function block in Codesys?

To add a function block in CODESYS, you navigate through the project menu by selecting Project → Add Object → POU, and then specify 'Function Block' as the type in the dialog box.

A function block (FB) is a powerful type of Program Organization Unit (POU) in CODESYS that allows for modular, reusable code. Unlike simple functions, a function block can retain its internal state between calls and can yield one or more values when executed. In the device tree or the POUs view, function block POUs are easily identifiable by their (FB) suffix.

Step-by-Step Guide to Adding a Function Block

Adding a new function block to your CODESYS project is a straightforward process. Follow these steps:

1. Open Your CODESYS Project: Launch CODESYS and open the project where you want to add the function block.
2. Access the Project Menu: In the top menu bar of the CODESYS environment, click on Project.
3. Initiate Adding an Object: From the dropdown menu, select Add Object.
4. Choose POU: In the subsequent submenu, click on POU... (Program Organization Unit).
5. Configure the New POU: A "Add POU" dialog box will appear. Here, you'll define the properties of your new function block:
   • Name: Enter a unique and descriptive name for your function block (e.g., MotorControlFB, PID_Controller, DebounceInput).
   • Type: Select Function Block from the dropdown list. This is crucial for defining it as a stateful, reusable component.
   • Implementation Language: Choose the programming language you want to use for the function block's logic. Common choices include:
     • Structured Text (ST): Ideal for complex algorithms and calculations.
     • Function Block Diagram (FBD): Visual representation, good for control flow.
     • Ladder Diagram (LD): Mimics traditional relay logic, common in industrial control.
     • Sequential Function Chart (SFC): For sequential processes and state machines.
     • Continuous Function Chart (CFC): For parallel execution blocks, similar to FBD but allows free positioning.
   • Options: Depending on your CODESYS version or selected language, you might see additional options like "Implement interface automatically." You can usually leave these as default unless you have specific requirements.
6. Confirm Addition: Click the Add button.

Once added, the new function block will appear in the "POUs" section of your CODESYS device tree and project organizer. You can then double-click it to open its editor and begin writing your logic.

Key Considerations for Function Blocks

Function blocks are central to structured programming in industrial automation. Understanding their characteristics is vital:

• Statefulness: The primary differentiator for a function block is its ability to retain values of its internal variables between execution cycles. This makes them perfect for components that need memory, like counters, timers, or state machines.
• Reusability: Function blocks are designed to be instantiated multiple times. Each instance gets its own set of internal variables, allowing you to use the same logic for different physical or logical components (e.g., multiple motors, various PID loops) without duplicating code.
• Encapsulation: They encapsulate specific functionalities, hiding the internal complexity from the calling program. This promotes modularity and makes your code easier to manage and debug.
• Input and Output Variables: You define input and output variables (VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT) to communicate with the calling POU, making the interface clear and well-defined.

Example Scenario

Imagine you are controlling multiple motors in a system. Instead of writing separate start/stop logic, error handling, and status monitoring for each motor, you can create a single MotorControlFB. For each motor, you would then declare an instance of this MotorControlFB in your main program, such as Motor1_FB : MotorControlFB; and Motor2_FB : MotorControlFB;. Each instance operates independently, simplifying development and maintenance.

Benefits of Using Function Blocks

• Modular Programming: Breaks down complex control tasks into smaller, manageable, and isolated units.
• Code Reusability: Reduces development time and effort by allowing you to reuse proven code blocks across different parts of your project or even in other projects.
• Easier Debugging and Maintenance: Isolated logic in FBs makes it simpler to identify and fix issues. Changes to one FB do not inadvertently affect other, unrelated parts of the program.
• Standardization: Promotes consistent programming practices and can lead to the creation of libraries of standard function blocks.

POU Type Comparison

To further clarify, here's a quick comparison of the main POU types in CODESYS:

POU Type	Description	Stateful	Returns Value	Reusability	Suffix (in CODESYS)
Function Block	Reusable block of code that maintains its state between calls.	Yes	Yes (multiple)	Highly Reusable	(FB)
Function	Reusable block of code that does not maintain state and returns a single value.	No	Yes (single)	Highly Reusable	(FUN)
Program	The main execution unit within a task; can instantiate FBs and call functions. Maintains state.	Yes	No	Less Reusable	(PRG)

By following these steps, you can effectively integrate function blocks into your CODESYS projects, enhancing structure, reusability, and overall code quality.