Rockwell Automation 1761 MicroLogix 1000 Programmable Controllers - Manual (Page 205)

Using Application Specific Instructions
11–17
Note that STI execution time adds directly to the overall scan time. During the
latency period, the controller is performing operations that cannot be disturbed by
the STI interrupt function.
Interrupt Priorities
Interrupt priorities are as follows:
1. User Fault Routine
2. High-Speed Counter
3. Selectable Timed Interrupt
An executing interrupt can only be interrupted by an interrupt having a 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
Programming