Allen-Bradley 1756-L61 ControlLogix 5561 Programming Manual page 32

Chapter 2 Organizing Tags
Table 4 - Tag Guidelines
Table 5 - Guideline
Limit a tag name to 40 characters
Use mixed case
Consider the alphabetical order of tags
Using extended properties in logic
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Details
Here are the rules for a tag name:
·Only alphabetic characters (A-Z or a-z), numeric characters (0...9),
and underscores (_)
·Must start with an alphabetic character or an underscore
·No more than 40 characters
·No consecutive or trailing underscore characters (_)
·Not case sensitive
Although tags are not case sensitive (upper case A is the same as lower case a), mixed case is easier to read.
These tags are easier to read
Tank_1
Tank1
Logix Designer application displays tags of the same scope in alphabetical order. To make it easier to monitor related
tags, use similar starting characters for tags that you want to keep together.
Starting each tag for a tank with
'Tank' keeps the tags together.
Tag Name
Tank_North
Tank_South
...
You can access limit extended properties defined on tags using the .@Min and .@Max syntax. However, you cannot
write to extended properties values in logic.
For example:
In the Ladder Editor, you can use limit extended properties on an instruction's source operand.
Rockwell Automation Publication 1756-PM004D-EN-P - September 2012
Than these tags
TANK_1
TANK1
tank_1
tank1
Otherwise, the tags may end up
separated from each other.
Tag Name
North_Tank
...
Other tags that start with
...
the letters o, p, q, and so
forth.
...
South_Tank