Allen-Bradley LOGIX 5000 Reference Manual page 323

Filter
Execution
Function Block
Condition/State Action Taken
Prescan EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false EnableIn and EnableOut bits are cleared to false.
Structured Text: NA
Tag.EnableIn is true EnableIn and EnableOut bits are set to true.
The instruction executes.
Instruction first run N/A
Instruction first scan Recalculate coefficients.
Postscan EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition/State Action Taken
Prescan See Prescan in the Function Block table.
Normal Execution See Tag.EnableIn is true in the Function Block table.
Postscan See Postscan in the Function Block table.
Examples
This example is the minimal legal programming of the DERV function block and
is only used to show the neutral text and generated code for this instruction.
This is for internal purposes only and is not a testable case.
Function Block
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Chapter 3
323