656 Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Appendix B Function Block Attributes
Use the table to choose your function block elements.
Latching Data
If you use an IREF to specify input data for a function block instruction, the data
in that IREF is latched for the scan of the function block routine. The IREF
latches data from program-scoped and controller-scoped tags. The controller
updates all IREF data at the beginning of each scan.
In this example, the value of tagA is stored at the beginning of the routine’s
execution. The stored value is used when Block_01 executes. The same stored
value is also used when Blcock_02 executes. If the value of tagA changes during
execution of the routine, the stored value of tagA in the IREF does not change
until the next execution of the routine.
If you want to Use a
Supply a value from an input device or tag Input reference (IREF)
Send a value to an output device or tag Output reference (OREF)
Perform an operation on an input value or values and
produce an output value or values
Function block
Transfer data between function blocks when they are:
·Far apart on the same sheet
·On different sheets within the same routine
Output wire connector (OCON) and an input wire connector
(ICON)
Disperse data to several points in the routine Single output wire connector (OCON) and multiple input
wire connectors (ICON)
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