Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 27)

Organize tags Chapter 2
Program parameters are similar to tags:
• You create program parameters at the program level, and use them to
manage data.
• Program parameters behave like controller-scope tags in that they can pass
data between programs.
Among other benefits, program parameters allow you to clearly define the inputs
to the routines in a program, and the outputs from those routines. Input and
Output parameters also automatically buffer data, so that you do not have to
create separate tags to buffer IO data.
If you want to restrict data to only the local program scope, you can use local tags.
See Tag scope on page 25 .
For more information on program parameters, refer to the Logix5000 Controllers
Program Parameters Programming Manual , publication 1756-PM021 .
Use the following guidelines to create tags for a Logix5000 project.
Guideline Details
Create user-defined data types User-defined data types (structures) let you organize data to match your machine or process. A user-defined data
type provides these advantages:
• One tag contains all the data related to a specific aspect of your system. This keeps related data together and easy
to locate, regardless of its data type.
• Each individual piece of data (member) gets a descriptive name. This automatically creates an initial level of
documentation for your logic.
• You can use the data type to create multiple tags with the same data layout.
For example, use a user-defined data type to store all the parameters for a tank, including temperatures, pressures,
valve positions, and preset values. Then create a tag for each of your tanks based on that data type.
Program parameter scope
Guidelines for tags
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