Rockwell Automation AutoMax Enhanced Ladder Language Reference Manual - Manual (Page 215)

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In1 and In2 each can be an array variable or a simple variable/constant. You can place
the result in a simple or array variable.
When EN transitions from false to true, the instruction prepares to carry out the function
specified in Operation by latching (buffering) all parameters. If you have programmed
the array instruction to operate on the array elements over multiple program scans, the
first scan sets up the operation. Then, the operation is performed as programmed over
a series of scans until the operation is done.
As long as EN remains true, the instruction completes the operation on the specific
lengths (Length1 and Lenght2) of the variables in In1 and In2, operating on the number
of elements specified in Elems/Scan with each program scan.
A specified number of elements (Length_Out) is stored in Out. Index acts as a marker
indicating the last element of the array that was operated on during the last scan.