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Allen-Bradley ControlLogix Ethernet Driver Help


Global Tags are Logix Tags that have global scope in the controller. Any program or task can access Global Tags; however, the number of ways a Global Tag can be referenced depends on its Logix data type and the address format being used.

Program Tags

Program Tags are identical to Global Tags except that a Program Tag's scope is local to the program in which it is defined. Program Tags follow the same addressing rules and limitations as Global Tags, but are prefixed with the following notation:

Program: <program name> .

For example, Logix Tag "tag_1" in program "prog_1" would be addressed as "Program:prog_1.tag_1" in a Client/Server Tag address.

Structure Tag Addressing

Logix Structure Tags (Global or Program) are tags with one or more member tags. Member tags can be atomic or structured in nature.

<structure name> . <atomic-type tag>

This implies that a substructure would be addressed as:

<structure name> . <substructure name> .<atomic-type tag>

Arrays of structures would be addressed as:

<structure array name> [dim1, dim2, dim3] . <atomic-type tag>

This implies that an array of substructures would be addressed as:

<structure name> . <substructure array name> [dim1, dim2, dim3] . <atomic-type tag>

Note: The examples above are only a few of the addressing possibilities that involve structures, and are displayed to provide an introduction to structure addressing. For more information, refer to Allen-Bradley or Rockwell documentation.

Internal Tags

Internal Tags are not visible in the server configuration, but can be browsed by the OPC client and found under the <Channel Name>.<Device Name> group. The _CIPConnectionSizeRequested Tag reflects the CIP Connection Size that was requested. The _CIPConnectionSizeActual Tag reflects the actual CIP Connection Size that is in use. Its value will differ from the _CIPConnectionSizeRequested Tag if the value requested is not supported by the device. For more information on the Connection Size, refer to Logix Communications Parameters.

Note: The tags described in the table below are only valid for the ControlLogix 5500 and CompactLogix 5300 device models.


System Tag

Status Tag

Tag Name







Logix models, with the exception of Serial Gateway models.

Read/Writ- e*

Logix models, with the exception of Serial Gateway models.

Read Only

*This tag is Read Only for ENI Logix models.

Changing the CIP Connection Size

The _CIPConnectionSizeRequested Tag allows users to change the CIP Connection Size parameter in real time. Both the Connection Size parameter (located in the Logix Comm. Parameters tab in Device Properties) and the System Tag are configurable while clients are connected. Changes will be applied before the next Read/Write request is performed.

Predefined Term Tags The tags displayed in the table below can be used to obtain general processor information from a PLC.

Tag Name


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