CHAPTER 7 INTERRUPTION/EXCEPTION PROCESSING FUNCTION
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7.2
Non-Maskable Interrupts
A non-maskable interrupt request is acknowledged unconditionally, even when interrupts are in the interrupt
disabled (DI) status. An NMI is not subject to priority control and takes precedence over all the other interrupts.
A non-maskable interrupt request is input from the NMI pin. When the valid edge specified by bit 0 (ESN0) of
external interrupt mode register 0 (INTM0) is detected at the NMI pin, the interrupt occurs.
While the service program of the non-maskable interrupt is being executed (PSW.NP = 1), the acknowledgement
of another non-maskable interrupt request is held pending. The pending NMI is acknowledged after the original
service program of the non-maskable interrupt under execution has been terminated (by the RETI instruction), or
when PSW.NP is cleared to 0 by the LDSR instruction. Note that if two or more NMI requests are input during the
execution of the service program for an NMI, the number of NMIs that will be acknowledged after PSW.NP is cleared
to 0 is only one.
Remark
PSW.NP: The NP bit of the PSW register.