Allen-Bradley LOGIX 5000 Reference Manual page 135

Process Control Instructions
Execution
Function Block
Condition/State
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
In this example, a PIDE instruction executes in a slow, lower priority task because
it is a slow, temperature loop. The output of the PIDE instruction is a controller-
scoped tag because it becomes the input to an SRTP instruction. The SRTP
instruction executes in a faster, higher priority task so that the pulse outputs are
more accurate
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Action Taken
EnableIn and EnableOut bits are cleared to false.
EnableIn and EnableOut bits are cleared to false.
EnableIn and EnableOut bits are set to true.
The instruction executes.
N/A
HeatOut and CoolOut are cleared to false.
HeatTimePercent and CoolTimePercent are cleared to
0.0.
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 1
135