Rockwell Automation Publication 1756-PM004D-EN-P - September 2012 23
Chapter
2
Organizing Tags
Introduction
With a Logix5000controller, you use a tag (alphanumeric name) to address data
(variables).
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.
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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