CHAPTER 7 INTERRUPTION/EXCEPTION PROCESSING FUNCTION
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Figure 7-7. Example of Servicing Interrupt Requests Simultaneously Generated
Default priority
a > b > c
Main routine
EI
Interrupt request a (level 2)
Interrupt request b (level 1)
Interrupt request c (level 1)
Servicing of interrupt request b
.
.
Servicing of interrupt request c
Servicing of interrupt request a
Interrupt request b and c are
acknowledged first according to
their priorities.
Because the priorities of b and c are
the same, b is acknowledged first
according to the default priority.
NMI request
Caution
To perform multiple interrupt servicing, the values of the EIPC and EIPSW registers must be
saved before executing the EI instruction. When returning from multiple interrupt servicing,
restore the values of EIPC and EIPSW after executing the DI instruction.
