CHAPTER 5 INTERRUPT/EXCEPTION PROCESSING FUNCTION
User’s Manual U13850EJ4V0UM
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5.2 Non-Maskable Interrupt
A non-maskable interrupt is acknowledged unconditionally, even when interrupts are disabled (DI state). An NMI
is not subject to priority control and takes precedence over all other interrupts.
The following two non-maskable interrupt requests are available in the V850/SB2.
•
NMI pin input (NMI)
•
Non-maskable watchdog timer interrupt request (INTWDT)
When the valid edge specified by rising edge specification register 0 (EGP0) and falling edge specification register
0 (EGN0) is detected in the NMI pin, an interrupt occurs.
INTWDT functions as the non-maskable interrupt (INTWDT) only in the state that the WDTM4 bit of the watchdog
timer mode register (WDTM) is set to 1.
While the service routine of the non-maskable interrupt is being executed (PSW.NP = 1), the acknowledgement of
another non-maskable interrupt request is kept pending. The pending NMI is acknowledged after the original service
routine 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 routine for an NMI, the number of NMIs that will be acknowledged after PSW.NP goes to ‘‘0’’,
is only one.
Caution
If PSW.NP is cleared to 0 by the LDSR instruction during non-maskable interrupt servicing, the
interrupt afterwards cannot be acknowledged correctly.