IBM Personal System/2 65 SX User Manual

Miscellaneous
System
Functions
and
Ports
Nonmaskable Interrupt
The
Nonmaskable
interrupt
(NMI)
service
signals
the
system
microprocessor
that
a
parity
error,
a
channel
check,
a
system
channel
time-out,
or
a
system
watchdog
time-out
has
occurred.
The
NMI
service
stops
all
arbitration
on
the
bus
until
bit
6
of
the
Arbitration
register
(I/O
address
hex
0090)
is
set
to
0.
This
can
result
in
lost
data
or
an
overrun
error
on
some
I/O
devices.
The
NMI
service
masks
all
other
interrupts,
and
the
IRET
instruction
restores
the
interrupt
flag
to
the
state
it
was
in
before
the
interrupt.
A
system
reset
causes
a
reset
of
the
NMI.
The
NMI
requests
from
system-board
parity
and
channel
check
are
subject
to
mask
control
with
the
NMI
mask
bit
in
the
RT/CMOS
Address
and
NMI
Mask
register.
The
watchdog
timer
and
system
channel
time-out
are
not
masked
by
this
bit.
(See
“RT/CMOS
Address
and
NMI
Mask
Register
(Hex
0070)”
on
page
3-12.)
The
power-on
default
of
the
NMI
mask
is
1
(NMI
disabled).
Before
NMI
service
is
enabled
after
a
power-on
reset,
the
parity-check
and
channel-check
states
are
initialized
by
POST.
Warning:
The
operation
following
a
write
to
hex
0070
should
access
hex
0071;
otherwise,
intermittent
malfunctions
and
unreliable
operation
of
the
RT/CMOS
RAM
can
occur.
3-22
Model
65
System
Board
—
October
1990

IBM Personal System/2 65 SX Specifications

General

Brand	IBM
Model	Personal System/2 65 SX
Category	Desktop
Language	English