Interrupt Priorities; Status File Data Saved - Allen-Bradley SLC 500 Series Reference Manual
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Interrupt Priorities
Table 11.3 Interrupt Priorities
SLC 5/02 Processor
1. User Fault Routine
2. Selectable Timed Interrupt
Subroutine
3. Interrupt Subroutine (ISR)
An executing interrupt can only be interrupted by an interrupt having higher
priority.
Under certain conditions, though, it is possible for a lower
TIP
priority task to run during the DII execution.
Status File Data Saved
Data in the following words is saved on entry to the STI subroutine and
re-written upon exiting the STI subroutine.
• S:0 Arithmetic flags
• S:13 and S:14 Math register
• S:24 Index register
Understanding Interrupt Routines
SLC 5/03 and Higher Processors
1. User Fault Routine
2. Discrete Input Interrupt (DII)
3. Selectable Timed Interrupt
Subroutine
4. Interrupt Subroutine (ISR)
Publication 1747-RM001G-EN-P - November 2008
11-11
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