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CHAPTER 12 INTERRUPT FUNCTIONS
User’s Manual U15104EJ2V0UD
12.4 Interrupt Servicing Operations
12.4.1 Non-maskable interrupt request acknowledgement operation
A non-maskable interrupt request is unconditionally acknowledged even if in an interrupt request acknowledgement
disabled state. It does not undergo interrupt priority control and has the highest priority over all other interrupts.
If a non-maskable interrupt request is acknowledged, the acknowledged interrupt is saved to the stack, the program
status word (PSW) and the program counter (PC), in that order, the IE and ISP flags are reset to 0, and the vector
table contents are loaded into PC and branched.
A new non-maskable interrupt request generated during execution of a non-maskable interrupt servicing program
is acknowledged after the current execution of the non-maskable interrupt servicing program is terminated (following
RETI instruction execution) and one main routine instruction is executed. If a new non-maskable interrupt request
is generated twice or more during non-maskable interrupt servicing program execution, only one non-maskable
interrupt request is acknowledged after termination of the non-maskable interrupt servicing program execution.
Figure 12-7 shows the flowchart from generation of the non-maskable interrupt request to acknowledging it. Figure
12-8 shows the timing of acknowledging the non-maskable interrupt request, and Figure 12-9 shows the operation
performed if a more than one non-maskable interrupt request occurs.