IBM Personal System/2 60 User Manual

Bits 7, 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
These
bits
control
the
fixed-disk
activity
light.
Setting
either
bit
to
1
turns
the
fixed-disk
activity
light
on.
Setting
both
bits
to
0
turns
the
light
off.
The
power-on
reset
condition
of
each
bit
is
0.
Reserved.
This
read-only
bit
indicates
the
Watchdog
Timer
status.
When
this
bit
is
set
to
1,
a
Watchdog
time-out
has
occurred.
For
more
information
about
the
Watchdog
Timer,
refer
to
the
Hardware
Interface
Technical
Reference.
This
bit
provides
the
security
lock
for
the
secured
area
of
RT/CMOS.
Setting
this
bit
to
1
electrically
locks
the
8-byte,
power-on
password.
Once
this
bit
is
set
by
POST,
it
can
only
be
cleared
by
turning
the
system
off.
Reserved.
This
bit
is
used
to
enable
the
‘address
20’
signal
(A20)
when
the
microprocessor
is
in
the
real
address
mode.
When
this
bit
is
set
to
0,
A20
cannot
be
used
in
real
mode
addressing.
This
bit
is
set
to
0
during
a
system
reset.
This
bit
provides
an
alternate
method
of
resetting
the
system
microprocessor:
This
alternate
method
supports
operating
systems
requiring
faster
operation
than
was
provided
on
the
IBM
Personal
Computer
AT"
Resetting
the
system
microprocessor
is
used
to
switch
the
microprocessor
from
the
protected
mode
to
the
real
address
mode.
The
alternate
reset
takes
13.4
microseconds.
This
bit
is
set
to
0
either
by
a
system
reset
or
a
Write
operation.
When
a
Write
operation
changes
this
bit
from
0
to
1,
the
alternate
reset
pin
is
pulsed
high
for
100
to
125
nanoseconds.
The
reset
occurs
after
a
minimum
delay
of
6.72
microseconds.
While
the
reset
is
occurring,
the
latch
remains
set
so
that
POST
can
read
this
bit.
If
the
bit
is
0,
POST
assumes
the
system
was
just
powered
on.
If
the
bit
is
1,
POST
assumes
a
switch
from
the
protected
mode
to
the
real
mode has taken place.
Personal
Computer
AT
is
a
trademark
of
the
International
Business
Machines
Corporation.
3-22.
Model
60
System
Board
—
October
1990

IBM Personal System/2 60 Specifications

General

Brand	IBM
Model	Personal System/2 60
Category	Desktop
Language	English