Allen-Bradley 1756-L61 ControlLogix 5561 Programming Manual page 33

Organizing Tags Chapter 2
Table 4 - Tag Guidelines
Table 5 - Guideline
Using extended properties in logic (continued)
Details
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. If however, 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.
·Restrictions to adding extended properties in logic
The following restrictions apply when you use extended properties in logic.
Extended properties must be used as an input operand
Extended properties can be used 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 can not 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 Properties Pane.
Alias Tags with Extended Properties cannot be accessed in Logic
If alias tag extended properties are used in logic, the routine does not verify.
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