Resolve Data Flow Between Two Blocks; Create A One Scan Delay; Summary - Allen-Bradley Logix5000 Reference Manual

Appendix B Function Block Attributes
This is okay
Neither wire uses the Assume Data Available indicator.
Both wires use the Assume Data Available indicator.
660

Resolve Data Flow Between Two Blocks

If you use two or more wires to connect two blocks, use the same data flow
indicators for all of the wires between the two blocks.
Assume Data Available
Indicator

Create a One Scan Delay

To produce a one scan delay between blocks, use the Assume Data Available
indicator. In the following example, block 1 executes first. It uses the output from
block 2 that was produced in the previous scan of the routine.
2

Summary

A function block routine executes in this order.
1. The controller latches all data values in IREFs.
2. The controller executes the other function blocks in the order determined
by how they are wired.
3. The controller writes outputs in OREFs.
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
This is not okay
One wire uses the Assume Data Available indicator while the other wire
does not.
1
Assume Data Available Indicator