Logix5000 Controllers General Instructions - SLAC Confluence

642 Function Block AttributesUse the following table to choose your function block elements:zIf You Want Tosupply a value from an input device or tagsend a value to an output device or tagperform an operation on an input value or values andproduce an output value or valuestransfer data between function blocks when theyare:• far apart on the same sheet• on different sheets within the same routinedisperse data to several points in the routineUse ainput reference (IREF)output reference (OREF)function blockoutput wire connector (OCON) and an input wireconnector (ICON)single output wire connector (OCON) and multipleinput wire connectors (ICON)Latching DataIf you use an IREF to specify input data for a function blockinstruction, the data in that IREF is latched for the scan of the functionblock routine. The IREF latches data from program-scoped andcontroller-scoped tags. The controller updates all IREF data at thebeginning of each scan.IREFIn this example, the value of tagA is stored at the beginning of theroutine’s execution. The stored value is used when Block_01executes. The same stored value is also used when Blcock_02executes. If the value of tagA changes during execution of the routine,the stored value of tagA in the IREF does not change until the nextexecution of the routine.Block_01tagABlock_02Publication 1756-RM003I-EN-P - January 2007