When creating a Function Block, you can force the user to bind specific inputs otherwise, they will receive an error message when running Build.

Hi, as I understood your question (“throw a compiler error if a function block instance element variable is not assigned to a external variable from the calling task”), this is not possible as I know. Best regards!

Handling Required Inputs During Function Block Creation

Ask Questions Programming

kovarj (Jaroslav Kovar) December 16, 2025, 9:03am 3

Hi @HansP, I have marked the reply of Alex as an answer on your issue. If you have any additional questions or new findings, feel free to continue the discussion.

Topic		Replies	Views
Incorrect use of function blocks Programming automation-studio	1	140	November 19, 2025
Refresh / update of variable types Programming automation-studio	3	63	March 3, 2026
Incomplete Type Error for Library Function Blocks Programming automation-studio , library	7	274	May 6, 2025
Checking for Null Pointers in IEC Functions and Function Blocks How-To & Wikis automation-studio , structured-text	5	557	January 7, 2025
Optional function arguments Controls & Vision plc	4	149	July 4, 2025

Handling Required Inputs During Function Block Creation

Related topics