Rockwell Automation Logix5000 Controllers Function Block Diagram Programming Manual - Manual (Page 16)

Chapter 1 Program a Function Block Diagram
This is OK This is NOT OK
In this example, neither wire uses the Assume Data Available indicator.
In this example, both wires use the Assume Data Available indicator.
In this example, only one wire uses the Assume Data Available indicator.
Create a one scan delay
Use the Assume Data Available indicator to produce a one scan delay between
blocks. In this example, block 1 executes first. It uses the output from block 2 that
was produced in the previous scan of the routine.
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.
16 Rockwell Automation Publication 1756-PM009E-EN-P - October 2014