Allen-Bradley LOGIX 5000 Reference Manual page 279

Drives
Execution
Function Block
Condition
Prescan
Tag.EnableIn is false
Tag.EnableIn is true
Instruction first run
Instruction first scan
Postscan
Structured Text
Condition/State
Prescan
Normal Execution
Postscan
Example
The PI instruction is a regulating instruction with proportional and integral gain
components. The integral gain component is set by the user in radians/sec; this
sets the basic frequency response of the PI regulator. The proportional gain sets
the overall gain of the block, including the proportional AND integral gain of the
block.
Excluding initialization and holding/clamping functionality, the following
diagram shows the PI block's basic regulating loop while in the linear mode.
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Action Taken
EnableIn and EnableOut are cleared to false.
EnableIn and EnableOut bits are cleared to false.
EnableIn and EnableOut bit is set to true.
The instruction executes.
Out n-1 = 0
The algorithm used to calculate Out will not be
executed.
Out n-1 = 0
The algorithm used to calculate Out will not be
executed.
EnableIn and EnableOut bits are cleared to false.
Action Taken
See Prescan in the Function Block table.
See Tag.EnableIn is true in the Function Block table.
See Postscan in the Function Block table.
Chapter 2
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