Allen-Bradley 1756-L61 ControlLogix 5561 Programming Manual page 34

Chapter 2 Organizing Tags
Table 4 - Tag Guidelines
Table 5 - Guideline
Using extended properties in logic (continued)
32
Details
·Array Tags are constrained
A constraint on array tags apply if the array tag uses indirect addressing to access limit extended properties. If an
array tag is using indirect addressing to access limit extended properties in logic, the following conditions apply.
– If the Array Tag has limit extended properties configured, the extended properties are applied to any array
element that does not explicitly have that particular extended property configured. For example, if the MyArray
has Max configured to 100, then any element of the array that does not have Max configured inherits the value
of 100 when being used in logic. However, it will not be visible to you that the value inherited from MyArray is
configured in the tag properties.
– At least one array element must have specific limit extended property configured for indirectly referenced array
logic to verify. For example, if MyArray[x].@Max is being used in logic, at least one array element of MyArray[]
must have Max extended property configured if Max is not configured by MyArray. If this is not done, if you
attempt to access Max in logic on MyArray in logic, the routine does not verify.
– Under the following circumstances a data type default value is going to be used:
- Array is accessed programmatically with indirect reference.
- Array tag does not have the extended property configured.
- Member of array does not have the extended property configured. For example for Array of SINT type, when
max limit is called in logic for a member, the value 127 will be used.
·Removing Extended Properties
You cannot remove extended properties that are accessed in logic when the project is online with the controller.
The Max and Min check boxes in the Extended Properties box in the Tag Editor are unavailable. You have to go
offline in order to remove the extended properties.
Removing extended properties in logic on structure tags is unavailable at the tag level. For example, if MyUDTTag
has 2 members, Mem1 being a DINT and the Mem2 being a SINT, if you define limit extended properties in Logic
on both members, but are only accessing Max extended properties on Mem1, the Max check box is unavailable in
the Extended Properties box in the Tag Properties Pane for both members. You are not able to remove the Max
extended properties for MyUDTTag .Mem2 online.
The same applies for Array tags. If limit extended properties is define on an array element and that element is
accessed in logic, then limit extended properties cannot be removed from any of the array elements.
Rockwell Automation Publication 1756-PM004D-EN-P - September 2012