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Rockwell Automation Logix5000 Logix5000 Controllers Quick Start User Manual

Page 95

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Publication 1756-QS001E-EN-P - October 2009

95

Program a Project Offline Chapter 5

Take advantage of program-scoped tags.

If you want multiple tags with the same name, define each tag at the program scope
(program tags) for a different program. This lets you re-use both logic and tag names in
multiple programs.

Avoid using the same name for both a controller tag and a program tag. Within a
program, you cannot reference a controller tag if a tag of the same name exists as a
program tag for that program.

Certain tags must be controller scope (controller tag).

If you want to use the tag

Assign this scope

In more than one program in the project

controller scope (controller tags)

In a Message (MSG) instruction

To produce or consume data

To communicate with a PanelView terminal

None of the above

program scope (program tags)

For integers, use the DINT data type.

To increase the efficiency of your logic, minimize the use of SINT or INT data types.
Whenever possible, use the DINT data type for integers.

• A Logix5000 controller typically compares or manipulates values as 32-bit values

(DINTs or REALs).

• The controller typically converts a SINT or INT value to a DINT or REAL value

before it uses the value.

• If the destination is a SINT or INT tag, the controller typically converts the value

back to a SINT or INT value.

• The conversion to or from SINTs or INTs occurs automatically with no extra

programming. But it takes extra execution time and memory.

Guideline

Details

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