Rockwell Automation Logix5000 Program Parameters Programming Manual - Manual (Page 21)

Connecting program parameters Chapter 1
Another useful scenario for InOut parameters is for instructions whose tags can
only be placed at the controller scope, such as the Message (MSG) instruction.
InOut parameters can connect directly to the MSG instruction tags in the
controller scope.
Finally, InOut parameters are useful for programs that have a large data structure,
and you do not want to pass the whole structure by value.
General rules for using InOut parameters
The following are general rules when using InOut parameters.
• InOut parameters can only support one connection. You cannot configure
connections to any member of an InOut parameter.
• An InOut parameter can only be connected to an Output parameter if the
InOut parameter is configured as a constant.
• InOut parameters are passed by reference, which means they point to the
base tag. In other words, when an InOut parameter is used in logic, the
current value of the parameter connected to the InOut parameter is used.
• Connections to InOut parameters cannot be changed online, unless using
the Partial Import Online (PIO) functionality.
For more information on the InOut parameter connections that can be made, see
Program parameter connection rules on page 28 .
Rockwell Automation Publication 1756-PM021A-EN-P - October 2014 21