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CHAPTER 18
INTERRUPT FUNCTIONS
User’s Manual U12790EJ2V0UD
18.4 Interrupt Servicing Operations
18.4.1 Non-maskable interrupt request acknowledgment operation
A non-maskable interrupt request is unconditionally acknowledged even if in an interrupt request acknowledgment
disabled state. It does not undergo interrupt priority control and has the highest priority of all interrupts.
If a non-maskable interrupt request is acknowledged, the acknowledged interrupt is saved in 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 the PC and branched.
A new non-maskable interrupt request generated during execution of a non-maskable interrupt servicing program
is acknowledged after execution of the current non-maskable interrupt servicing program has finished (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 18-7 shows the flowchart from generation of a non-maskable interrupt request to acknowledgment. Figure
18-8 shows the timing of acknowledging the non-maskable interrupt request, and Figure 18-9 shows the operation
performed if a more than one non-maskable interrupt request occurs.