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CHAPTER 16 INTERRUPT AND TEST FUNCTIONS
User’s Manual U11302EJ4V0UM
16.4 Interrupt Servicing Operations
16.4.1 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 highest priority over all other interrupts.
If a non-maskable interrupt request is acknowledged, the contents of program status word (PSW) and program
counter (PC) are saved in the stacks in that order. Then, 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 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 service program execution, only one non-maskable interrupt
request is acknowledged after termination of the non-maskable interrupt service program execution.
Figure 16-9 shows the flowchart illustrating generation and acknowledgment of a non-maskable interrupt request.
Figure 16-10 shows the timing of acknowledging a non-maskable interrupt request. Figure 16-11 illustrates how
nested non-maskable interrupt requests are acknowledged.