Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 21)

Chapter 2
Organize tags
With a Logix5000 controller, you use a tag (alphanumeric name) to address data
(variables).
Term Definition
Tag A text-based name for an area of the controller’s memory where data is stored.
• Tags are the basic mechanism for allocating memory, referencing data from logic, and monitoring
data.
• The minimum memory allocation for a tag is four bytes.
• When you create a tag that stores data that requires less than four bytes, the controller allocates
four bytes, but the data only fills the part it needs.
The controller uses the tag name internally and does not need to cross-reference a
physical address.
• In conventional programmable controllers, a physical address identifies each
item of data.
• Addresses follow a fixed, numeric format that depends on the type of
data, such as N7:8, F8:3.
• Symbols are required to make logic easier to interpret.
• In Logix5000 controllers, there is no fixed, numeric format. The tag name
itself identifies the data. This lets you:
• Organize your data to mirror your machinery.
• Document (through tag names) your application as you develop it.
Introduction
Rock well Automati on Publication 1756- PM004E -EN-P - October 2014 21