Generic Variables and FDB

rmarco — Mon, 29 Jun 2026 12:12:04 -0000

Hello everyone,

I am running into a highly frustrating issue in the FBD editor regarding a Function Block with generic constants (VAR_GENERIC CONSTANT).

I created a FB using ST, with a generic var, useful for having a variable sized array, as follows:

FUNCTION_BLOCK Coil
VAR_GENERIC CONSTANT
    maxEvents: USINT := 5;
END_VAR
VAR
    events: ARRAY[0..maxEvents-1] OF IEvent;
END_VAR

These FBs have also several methods. I declare them as follows in code:

VAR
    coil1: CDL.Coil<(maxEvents:=1)>;
END_VAR

and when using them in ST, I have no problems. However, when trying to use them in FDB, I do not know how to do that, as some strange misalignment happens.

Here's what happens:
When I add the block to my FBD canvas and assign coil1 as the instance name, the compiler throws this error:
'coil1' is not an instance of 'CDL.Coil<(maxEvents:=1)>'.

Same occurs when I try to instantiate blocks such as 'coil1.turnOn' or similar.

Here is what I have already tried, none of which worked:
- Deleting the <(maxEvents:=1)> parameter from the text inside the FBD box.
- Deleting the block entirely, dropping an "Empty Box", and typing coil1 above it to let the IDE auto-complete and format the block.
- Running a full "Clean All" and rebuilding the code.

I am aware that I could bypass the graphical editor by calling it in Structured Text. However, I need to keep this logic compatible to FBD.

Has anyone encountered this specific FBD parsing bug with generic variables?

Thanks in advance for any insights.

Best regards,
Marco

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