30 Rockwell Automation Publication 1756-PM004D-EN-P - September 2012
Chapter 2 Organizing Tags
Limit a tag name to 40 characters 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
Use mixed case 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 Than these tags
Tank_1 TANK_1
Tan k1 TA NK1
tank_1
tank1
Consider the alphabetical order of tags 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.
Using extended properties in logic 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.
Table 4 - Tag Guidelines
Table 5 - Guideline Details
Starting each tag for a tank with
‘Tank’ keeps the tags together.
Tag Name
Tank_Nort h
Tank_South
…
Otherwise, the tags may end up
separated from each other.
Tag Name
North_Tank
…
…
…
South_Tank
Other tags that start with
the letters o, p, q, and so
forth.
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