Rockwell Automation Logix5000 Program Parameters Programming Manual - Manual (Page 20)

Chapter 1 Connecting program parameters
7. (optional) On the Tag Browser, clear one or more of the check boxes to
limit the number of available parameters that appear in the list.
8. In the Show parameters from other program list, choose the program to
which you want to connect this Output parameter.
9. In the list of available parameters, double-click the desired parameter.
10. Click OK.
An InOut parameter is a special usage program parameter that represents a
reference to data that can be used both as input and output during the execution
of a program. Because InOut parameters pass by reference rather than by value,
they are merely a pointer to the original data and closely resemble the behavior of
an alias tag. With that in mind, it is possible that the InOut parameter values
could change during the execution of a program. Depending on your task
structure, this behavior may be necessary.
InOut parameter connection types and uses
InOut parameters can be connected to Input parameters, Public parameters,
Output parameters (if InOut is constant), and controller scope tags.
An example of how InOut parameters are advantageous is an application that
contains multiple tasks with different priority assignments. In this scenario, a
lower priority task is interrupted by a higher priority task. If the higher priority
task is referencing data in the lower priority task, the InOut parameter allows the
higher priority task to point directly to a tag’s value in the lower priority task. This
ensures that the higher priority task is using the most up-to-date value of a tag.
InOut parameters
20 Rockwell Automation Publication 1756-PM021A-EN-P - October 2014