Allen-Bradley Logix5000 Reference Manual page 657

This example is the same as the one above. The value of tagA is stored only once
at the beginning of the routine's execution. The routine uses this stored value
throughout the routine.
Starting with RSLogix 5000 software, version 11, you can use the same tag in
multiple IREFs and an OREF in the same routine. Because the values of tags in
IREFs are latched every scan through the routine, all IREFs will use the same
value, even if an OREF obtains a different tag value during execution of the
routine.
In this example, if tagA has a value of 25.4 when the routine starts executing this
scan, and Block_01 changes the value of tagA to 50.9, the second IREF wired
into Block_02 will still use a value of 25.4 when Block_02 executes this scan. The
new tagA value of 50.9 will not be used by any IREFs in this routine until the
start of the next scan.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Function Block Attributes
Block_01
tagA
Block_02
tagA
Appendix B
657