Non-Maskable Interrupts - HP Vectra Reference Manual

Only one interrupt level may be active for each signal. The
duplicates must be masked off using the 8259A interrupt mask
register.
Non-maskable Interrupts
The non-maskable interrupt is used to process the system
response to a memory parity error, an error signaled by an
expansion card through the I/O CHCK signal, or a hard reset from
the keyboard. The signal is masked from the 80286 at system
reset, and must be enabled by the system software. The NMI
signal is enabled by setting bit 7 of port 70H to 0, or it can be
masked by setting the same bit 7 to 1.
The NMI generates a type 2 interrupt. The vector to the service
routine should be placed at 0000:0008H. Refer to the HP Vectra
Technical Reference Manual Volume
2:
System BIOS
for additional
information regarding programming considerations.
22 Processor Board