Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 30)

Chapter 2 Organize tags
Guideline Details
Using extended properties in logic (continued) In the Function Block Editor, you can access extended properties in logic by wiring an Input Reference to a block’s
input pins.
In the Structured Text Editor, you can access limit extended properties in logic on the right hand side of an
assignment operation or in a comparison statement. You can also access limit extended properties in logic when you
embed structured text in the Sequential Function Chart Editor.
You need to know which tags have limit extended properties associated with them as there is no indication in the
Tag Browser that extended properties are defined for a tag. However, if you try to use extended properties that have
not been defined for a tag, the editors show a visual indication (that is: a rung error in Ladder Logic, a verification
error X in Function Block Diagrams, and the error underlined in Structured Text) and the routine does not verify.
• The following restrictions apply when you use extended properties in logic.
− You must use extended properties as an input operand.
You can use extended properties on an instruction as long as the input (source) operand is a non-boolean
atomic data type. That is, if an instruction has operands whose data type is non-atomic or BOOL, limit
extended properties cannot be used. For example, the ALMD instruction in Ladder Logic does not support
extended properties because its configurable operands are of type BOOL.
In the Ladder Editor, when limit extended properties is used in logic, the value field associated with the source
operand is unavailable. You can change the tag's extended properties only in the Tag Editor Properties Pane.
− You cannot access alias tags with extended properties in logic.
If you use alias tag extended properties in logic, the routine does not verify.
30 Rockwell Automation Publication 1756-PM004E-EN-P - October 2014