During the development of a function block type, its declarations may be in an intermediate state which, if compiled, could produce behaviors that would be contrary to the design intent and may even lead to failure of the control system with accompanying damage or unsafe operation of the controlled machine or process. The FBDK provides a validation tool to help you avoid the compilation of such invalid FB types. Errors detected by this tool include:

• Invalid or missing declarations in Execution Control Charts (ECCs) of Basic FB types.
• Unused event and data inputs and outputs for Basic, Composite and Service Interface FB Types.
• Unused internal variables for Basic FB types.

As shown in the figure below, access to this tool is provided by the Validate item in the popup menu of the FB type's viewport.

Application of this tool to the Basic FB template produces the result shown below. QI and QO are identified as unused variables because no algorithms or EC transitions using these variables are defined in this template.