User Manual
Table Of Contents
- Logix5000 Controllers I/O and Tag Data
- Summary of changes
- Table of contents
- Preface
- Communicate with I/O modules
- Organize tags
- Force I/O
- Data access control
- Introduction
- External access
- Configure external access
- External access availability
- User-defined type considerations
- Add-on instructions external access considerations
- Tag mapping considerations
- Imported tag behavior
- Constant value tags
- Configure constant tags
- Constant check box availability
- Add-on instructions constant value considerations
- Index
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
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