Installation manual

Publication 1747-RM001G-EN-P - November 2008
Understanding Interrupt Routines 11-11
Interrupt Priorities
An executing interrupt can only be interrupted by an interrupt having higher
priority.
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
Table 11.3 Interrupt Priorities
SLC 5/02 Processor SLC 5/03 and Higher Processors
1. User Fault Routine 1. User Fault Routine
2. Selectable Timed Interrupt
Subroutine
2. Discrete Input Interrupt (DII)
3. Interrupt Subroutine (ISR) 3. Selectable Timed Interrupt
Subroutine
4. Interrupt Subroutine (ISR)
TIP
Under certain conditions, though, it is possible for a lower
priority task to run during the DII execution.