Allen-Bradley 1756-L65 ControlLogix 5565, Programming Manual

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48 Rockwell Automation Publication 1756-PM004D-EN-P - September 2012
Chapter 2 Organizing Tags
Alias Tags
An alias tag lets you create one tag that represents another tag.
·
Both tags share the same value.
·
When the value of one of the tags changes, the other tag reflects the change
as well.
Use aliases in the following situations:
·
Program logic in advance of wiring diagrams.
·
Assign a descriptive name to an I/O device.
·
Provide a more simple name for a complex tag.
·
Use a descriptive name for an element of an array.
The tags window displays alias information.
A common use of alias tags is to program logic before wiring diagrams are
available.
1.
For each I/O device, create a tag with a name that describes the device,
such as conveyor for the conveyor motor.
2.
Program your logic by using the descriptive tag names.
You can even test your logic without connecting to the I/O.
3. Later, when wiring diagrams are available, add the I/O modules to the I/O
configuration of the controller.
4. Finally, convert the descriptive tags to aliases for their respective I/O
points or channels.
drill_1_depth_limit is an alias for
Local:2:I.Data.3 (a digital input point).
When the input turns on, the alias tag
also turns on.
drill_1_on is an alias for
Local:0:O.Data.2 (a digital output
point). When the alias tag turns on, the
output tag also turns on.
north_tank is an alias for tanks[0,1].
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The (C) indicates that the tag is at the controller scope.