Rockwell Automation Logix5000 Program Parameters Programming Manual - Manual (Page 12)

Chapter 1 Connecting program parameters
User-defined type sub-element connection considerations
User-defined types (UDTs) used as parameters can contain member-specific
connections. To ensure proper data flow, the base Usage can only be specified at
the base of the UDT, and not at the member level, as the following example shows.
An Input parameter is a parameter that defines the data that is passed by value
into an executing program. Since Input parameters are passed by value, their
values cannot change from external sources during the execution of the program.
An Input parameter supports a maximum of one sourcing connection.
Input parameter connection types and uses
Input parameters can be connected to Output parameters, Public parameters,
InOut parameters, and controller scope tags. This makes Input parameters a great
option for connecting input card data to a code module or object. It also is a good
option for code module or object commands that are point-to-point.
General rules for using Input parameters
The following are general rules when using Input parameters.
• Input parameters (including members) can only support one sourcing
connection. This means that only one source can be delivering the value to
the input parameter.
• Input parameter values are refreshed before each scan of a program. The
values do not change during the logic execution, so you do not need to write
code to buffer inputs.
• A program can write to its own Input parameters.
• Data values for Output parameters that are connected to controller scope
tags or Public parameters are copied after the scan of a program. In a project
with multiple tasks, the data copy for a parameter that is of type BOOL,
SINT, INT, DINT, LINT, or REAL will not be interrupted. The data copy
from an Output parameter to a controller scope tag or Public parameter or
any other predefined or user-defined data type may be interrupted by a task
switch.
Input parameters
12 Rockwell Automation Publication 1756-PM021A-EN-P - October 2014