dl-breadcrumbs__homedl-breadcrumb-item__separatorConfiguration and programmingdl-breadcrumb-item__separatorProgramming with CODESYSdl-breadcrumb-item__separatorCODESYS Development Systemdl-breadcrumb-item__separator...dl-breadcrumb-item__separatorReference, User Interfacedl-breadcrumb-item__separatorObjectsdl-breadcrumb-item__separatorObject 'POU'dl-breadcrumb-item__separatorGeneral
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General

Symbol: _cds_icon_pou

An object of the type “POU” is a Program Organization Unit in a CODESYS project. You write source code for your controller program in POUs.

There are the following types of POUs:

  • Program

  • Function

  • Function block

A “POU” object is inserted by using the command “Project  Add Object” in the Device tree or in the “POUs” view. When adding a POU you define the POU type and the implementation language.

You can also add other programming objects (method, action, etc.) to these objects.

Calling POUs

Certain POUs can call other POUs. Recursions are not permitted.

When calling POUs via the namespace, CODESYS browses the project for the POU to be called in accordance with the following order:

  1. Current application

  2. “Library Manager” of the current application

  3. “POUs” view

  4. “Library Manager” in the “POUs” view

If you want to call a POU that exists with the same name in a library used in the application and as an object in the “POUs” view, note the following: There is no syntax that allows you to call the POU in the “POUs” view only by its name. In this case you must shift the library from the application's library manager to the project's library manager (in the “POUs” view). After that you can call the POU object in the “POUs” view purely by its name. If you add the namespace to the library, you can call the POU of the library.

The term “POU” is also used in CODESYS for the “POUs” view in which CODESYS manages the global objects in the project.

Dialog 'Add POU'

Function: The dialog is used to configure a new POU according to the IEC 61131-3 standard. This means that a POU can be a program, a function, or a function block.

Call: “Project  Add Object” menu; context menu in the “Devices” view when an application is selected; context menu in the “POUs” view

“Name”

Name of POU
Table 464: “Type”

“Program”

“Function Block”

  • _cds_icon_option_activated “Extends”: Specification or selection of a base function module in the sense of object-oriented programming. Specified with the EXTENDS keyword in the function block declaration

  • _cds_icon_option_activated “Implements”: Specification or selection of an interface in the sense of object-oriented programming. Specified with the IMPLEMENTS keyword in the function block declaration. When the POU is created, all methods are created which are defined via the interface.

  • _cds_icon_option_activated “Final”: Derived access is not allowed. This means that you cannot extend the function block with another function block. This allows for optimized code generation.

  • _cds_icon_option_activated “Abstract”: Identifies that the function block has a missing or incomplete implementation and cannot be instantiated. Abstract FBs are used exclusively as base function blocks and the implementation typically occurs in a derived FB. If a non-abstract function block is created, which in turn extends an abstract function block, then all abstract methods of the abstract basic function block are added to the new function block as (non-abstract) methods.

  • “Access specifier”

    • “PUBLIC”: Corresponds to the specification of no access specifier.

    • “INTERNAL”: Access to the function block is restricted to the namespace (library).

  • “Method implementation language”: When you select the “Implements” option, you can select an implementation language here for all method objects that CODESYS generates by means of the implementation of the interface.

    The “Method implementation language” does not depend on the implementation language of the function block.

“Function”

Note: Not available when “Sequential Function Chart (SFC)” is selected as the “Implementation language”.

“Return type:”: Data type of the return value

“Implementation language”

Implementation language of the POU