Allen-Bradley 1756-L65 ControlLogix 5565, Programming Manual

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82 Rockwell Automation Publication 1756-PM004D-EN-P - September 2012
Chapter 4 Data Access Control
Add-On Instructions Constant
Value Considerations
The Constant attribute applies only to InOut parameters. The default setting of
the property will be
not a Constant Value .
The Constant attribute will not apply to Input, Output, EnableIn and EnableOut
Add-On Instruction parameters. It will not apply to Add-On Instruction Local
tags.
By denoting an InOut parameter of an Add-On Instruction as a constant, it
means that within the Add-On Instruction, that parameter cannot be written to.
The project will fail verification if this type of write is attempted.
Appropriate usage of Constant tags is monitored by logic verification.