NEC PD78F9488 - Manual (Page 301)

CHAPTER 16 INTERRUPT FUNCTIONS
User’s Manual U15331EJ4V1UD
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16.4 Interrupt Servicing Operation
16.4.1 Non-maskable interrupt request acknowledgment operation
The non-maskable interrupt request is unconditionally acknowledged even when interrupts are disabled. It is not
subject to interrupt priority control and takes precedence over all other interrupts.
When the non-maskable interrupt request is acknowledged, the PSW and PC are saved to the stack in that order,
the IE flag is reset to 0, the contents of the vector table are loaded to the PC, and then program execution branches.
Figure 16-10 shows the flow from non-maskable interrupt request generation to acknowledgment, Figure 16-11
shows the timing of non-maskable interrupt acknowledgment, and Figure 16-12 shows the acknowledgment operation
when a number of non-maskable interrupts are generated.
Caution During non-maskable interrupt service program execution, do not input another non-maskable
interrupt request; if it is input, the service program will be interrupted and the new non-
maskable interrupt request will be acknowledged.