Rockwell Automation Logix5000 Program Parameters Programming Manual - Manual (Page 16)

Chapter 1 Connecting program parameters
An Output parameter is a parameter that defines the data that is produced as a
direct result of executing a program. Since Output parameters are always passed by
value, their values only change at the end of the scan of a program when the copy
of the parameters has executed.
Tip: If using direct access another program can be a source for an Output parameter.
Output parameter connection types and uses
Output parameters can be connected to one or more Input parameters, Public
parameters, InOut parameters (constants), and controller scope tags, which makes
Output parameters a great option for connecting a code module or object to an
output card. It also is a good option for configuring a code module or object to
invoke operations (such as commands and settings) in other code modules or
objects. Additionally, multiple connections can be configured for an Output
parameter (known as fanning), which allows one code module or object to send
multiple commands to multiple modules or objects using one Output parameter.
General rules for using Output parameters
The following are general rules when using Output parameters.
• Output parameters, including members, can support multiple connections.
For example, assume you have a BOOL Input parameter in Program_A
named Input1a, and a BOOL Input parameter in Program_B named
Input1b. You are allowed to connect a single Output parameter in
Program_C to both Input1a and Input1b. This is known as fanout.
• Output parameter values are refreshed after each scan of a program. They
maintain the value from the previous scan until the program execution is
complete.
• Output parameters connected to Public parameters or controller scope tags
are copied (pushed) at the end of the program execution.
• An Output parameter can only be connected to an InOut parameter if the
InOut parameter is configured as a constant.
Tip: InOut parameters are passed by reference, which means they point to the base tag. That is, when an
InOut parameter is used in logic, the current value of the parameter connected to the InOut parameter
is used.
For more information on the Output parameter connections that can be made, see
Program parameter connection rules on page 28 .
Output parameters
16 Rockwell Automation Publication 1756-PM021A-EN-P - October 2014