Rockwell Automation Logix5000 Program Parameters Programming Manual - Manual (Page 24)

Chapter 1 Connecting program parameters
Public parameters are updated as the source updates, so higher priority tasks that
interrupt a program during execution have access to any updated values in the
lower priority task. Additionally, fan-in is supported with Public parameters,
which is useful in situations where a code module or object could receive a
command from many modules or objects. Input parameters can be used, but an
individual Input parameter is required for each connection. In other words, if a
code module or object had a command that could be invoked by 10 different code
modules or objects then 10 input parameters are required. However, if the
command is configured as a Public parameter, then all 10 code modules or objects
could have an Output parameter connected to a single Public parameter.
General rules for using Public parameters
The following are general rules when using Public parameters.
• Public parameters can support multiple connections. You can configure
connections to the base Public parameter or any member of a Public
parameter, including User-defined structures.
• Public parameters are updated when the source is updated. In other words,
when a Public parameter value updates, it is immediately available to any
higher priority tasks that are connected to that parameter.
• While Public parameters cannot be connected to controller scope tags, they
can be aliased to controller scope tags. If this functionality is desired, it is
important to remember that the alias updates asynchronous to program
execution. The Public parameter contains the real-time value of the
controller scope tag.
For more information on the Public parameter connections that can be made, see
Program parameter connection rules on page 28 .
24 Rockwell Automation Publication 1756-PM021A-EN-P - October 2014