Allen-Bradley 1756-L65 ControlLogix 5565, Programming Manual

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Rockwell Automation Publication 1756-PM004D-EN-P - September 2012 27
Organizing Tags Chapter 2
Scope
When you create a tag, you define it as either a controller tag (global data) or a
program tag for a specific program (local data).
A Logix5000 controller lets you divide your application into multiple programs,
each with its own data. There is no need to manage conflicting tag names
between programs. This makes it easier to reuse both code and tag names in
multiple programs.
Controller tags
(Global data)
Task
Program
Project
Other routines
Main routine
I/O data
Program tags (Local
data)
System-shared data
Controller tags (Global data)
Program_A
Other routines
Main routine
Tag_4
Tag_5
Tag_6
Program tags (Local
data)
Tag_1
Tag_2
Tag_3
Program_B
Other routines
Main routine
Tag_4
Tag_5
Tag_6
Program tags (Local
data)
Data at the program scope is isolated from other programs.
· Routines cannot access data that is at the program scope of another program.
· You can reuse the tag name of a program-scoped tag in multiple programs.
For example, both Program_A and Program_B can have a program tag named Tag_4.
Data
All programs have access to data that is at
the controller scope.