CHAPTER 14 INTERRUPT FUNCTIONS
14.4 Interrupt Servicing Operation
14.4.1 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, 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 14-9 shows the flow from non-maskable interrupt request generation to acknowledgement, Figure 14-10
shows the timing of non-maskable interrupt acknowledgement, and Figure 14-11 shows the acknowledgement
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.
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