Rockwell Automation Logix5000 Controllers Function Block Diagram Programming Manual - Manual (Page 13)

Program a Function Block Diagram Chapter 1
The new tagA value of 50.9 is not used by any IREFs in this routine until the start
of the next scan.
Order of execution
The Logix Designer application automatically determines the order of execution
for the function blocks in a routine.
• When you verify a function block routine.
• When you verify a project that contains a function block routine.
• When you download a project that contains a function block routine.
Define the order of execution by wiring function blocks together and indicating
the data flow of any feedback wires, if necessary.
If function blocks are not wired together, it does not matter which block executes
first. There is no data flow between the blocks.
If the blocks are wired sequentially, the order of execution moves from input to
output. The inputs of a block require data to be available before the controller can
execute that block. In this example, block 2 has to execute before block 3 because
the outputs of block 2 feed the inputs of block 3.
Rockwell Automation Publication 1756-PM009E-EN-P - October 2014 13