250 Rockwell Automation Publication 2080-UM002L-EN-E - November 2021
Appendix D User Interrupts
An interrupt must be configured and enabled to execute. When any one of the
interrupts is configured (and enabled) and subsequently occurs, the user
program:
1. suspends its execution of the current POU,
2. performs a predefined POU based on which interrupt occurred, and
3. returns to the suspended operation.
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.
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
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