25Publication 1756-PM004C-EN-P - October 2009 25
Chapter
2
Organize Tags
Introduction
With a Logix5000 controller, you use a tag (alphanumeric name) to address
data (variables).
The controller uses the tag name internally and doesn’t 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 depend 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.
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.
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