A runtime system can include the implementation of a function block, function, or method (for example, from a library). If you create a POU in your application with the same name by using the “External implementation” without an implementation, then you can execute the existing implementation. Note here that you declare local variables only in an external function block. External functions and methods must not contain local variables.
When the application is downloading, CODESYS searches for and links the associated implementation in the runtime system for each external POU.
Objects with the property “External implementation” are postfixed with (EXT) after the object name in the “Devices” or “POUs” view.
For more information, see: ⮫ “Dialog: Properties: Build ”
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Creating POUs with external implementation
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Creating methods with external implementation