In this tips and tricks post I will demonstrate the usage of the attribute: ‘instance-path’. The instance path attribute allows you to get the instance path of the containing POU in a string variable. Something I find particularly useful for error-logs and debug messages.
How to use it
1. We need a string variable which will receive the instance path, in this example we call it ‘Path’.
2. We give the variable ‘Path’ the pragma ‘{attribute ‘instance-path’}’, we also give it the pragma ‘{attribute ‘noinit’}’ to let the compiler know that this variable should not be implicitly assigned.
3. The containing POU gets the pragma ‘{attribute ‘reflection’}’ to let the program know it should search for instance-path variables within this POU.
Example:
{attribute 'reflection'}
FUNCTION_BLOCK POU
VAR
{attribute 'instance-path'}
{attribute 'noinit'}
Path : STRING;
Error : STRING;
END_VAR
Error := CONCAT('Error occurred at ', Path);
Running this in the PLC gives us a error message with details about the place where the error occurred:
Conclusion
This short tips and tricks post showed the usage the instance path attribute. A attribute particularly useful for more detailed logs and error messages. More information about the instance path attribute can be found here.
