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Learning about Naming Logix Tags

Logix tag naming conventions follow IEC 1131-3 identifier rules. Tag names are not case sensitive. Tag names must also:

  • Begin with an alphabetic character (A to Z or a to z) or an underscore (_).
  • Contain only alphabetic characters, numeric characters, and/or underscores.
  • Contain 40 or fewer characters.
  • Avoid using consecutive or trailing underscores.

You may also add tag descriptions. Descriptions may contain:

  • 120 or fewer characters.
  • Any printable character.

Accessing I/O under Controller Scope uses the following format:

Location:SlotNumber:Type.MemberName.SubMemberName.Bit where:

This address variable Specifies
Location Identifies network location:
  • LOCAL=local chassis.
  • ADAPTER_NAME=identifies remote chassis communication adapter or bridge module.
SlotNumber Slot number of I/O module in its chassis.
Type Type of data:
  • I=input
  • 0=output
  • C=configuration
  • S=status
MemberName Specific data from the I/ O module; this depends on what type of data the module can store. For example. Data and Fault are possible fields of data for an I/O module. Data is the common name for values that are sent to, or received from, I/O points.
SubMemberName Specific data related to a MemberName.
Bit (optional) Specific point on the I/O module; this depends on the size of the I/O module (0 to 31 for a 32-point module).

Accessing tags under Controller Scope uses the following format:

TagName.SubTagName where:

This address variable Is:
TagName User-defined tag name.
SubTagName Specific data related to TagName.

Accessing tags under Program Scope uses the following format:

PROGRAM:ProgramName.TagName.SubTagName where:

This address variable Is:
ProgramName Name of user-defined program.
TagName User-defined tag name.
SubTagName Specific data related to TagName.

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