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296 Rockwell Automation Publication 2080-UM002N-EN-E - November 2022
Appendix C User Interrupts
Specifically, if the controller program is executing normally and an interrupt event occurs:
1. The controller stops its normal execution.
2. Determines which interrupt occurred.
3. Goes immediately to the beginning of the POU specified for that User Interrupt.
4. Begins executing the User Interrupt POU (or set of POU/function blocks if the specified
POU calls a subsequent function block).
5. Completes the POU.
6. Resumes normal execution from the point where the controller program was
interrupted.
When Can the Controller Operation be Interrupted?
The Micro830 controllers allow interrupts to be serviced at any point of a program scan. Use
UID/ UIE instructions to protect program block that should not be interrupted.
Priority of User Interrupts
When multiple interrupts occur, the interrupts are serviced based on their individual priority.
When an interrupt occurs and another interrupt(s) has already occurred but has not been
serviced, the new interrupt is scheduled for execution based on its priority relative to the
other pending interrupts. At the next point in time when an interrupt can be serviced, all the
interrupts are executed in the sequence of highest priority to lowest priority.
If an interrupt occurs while a lower priority interrupt is being serviced (executed), the currently
executing interrupt routine is suspended, and the higher priority interrupt is serviced. Then
the lower priority interrupt is allowed to complete before returning to normal processing.
If an interrupt occurs while a higher priority interrupt is being serviced (executed), and the
pending bit has been set for the lower priority interrupt, the currently executing interrupt
routine continues to completion. Then the lower priority interrupt runs before returning to
normal processing.
Table 71 - Priorities From Highest to Lowest
User Fault Routine Highest Priority
Event Interrupt0
Event Interrupt1
Event Interrupt2
Event Interrupt3
High-Speed Counter Interrupt0
High-Speed Counter Interrupt1
High-Speed Counter Interrupt2
High-Speed Counter Interrupt3
High-Speed Counter Interrupt4
High-Speed Counter Interrupt5
Interrupt Operation Example
POU 2 is the main control program.
POU 10 is the interrupt routine.
• An Interrupt Event occurs at rung 123.
• POU 10 is executed.
• POU 2 execution resumes immediately after POU
10 is scanned.
rung 0
rung 123
rung 275
POU 2
POU 10