Process Control Instructions
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 109
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.
Tag.EnableIn is true EnableIn and EnableOut bits are set to true.
The instruction executes.
Instruction first run N/A
Instruction first scan OpenTime and CloseTime are cleared to 0.0.
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
Example 1
In this example, the POSP instruction opens or closes a motor-operated valve
based on the CVEU output of the PIDE instruction. The actual valve position is
wired into the Position input and optional limit switches, which show if the valve
is fully opened or closed, are wired into the OpenedFB and ClosedFB inputs. The
OpenOut and CloseOut outputs are wired to the open and close contacts on the
motor-operated valve.
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