IBM Personal System/2 50 User Manual

Card Selected Feedback
When
the
adapter
is
addressed,
it
responds
by
setting
the
‘-card
selected
feedback’
signal
(-CD
SFDBK)
to
active.
-CD
SFDBK
is
derived
from
the
address
decode
and
driven
by
a
totem
pole
driver.
Itis
latched
by
the
system
board
and
can
be
read
through
the
Card
Selected
Feedback
register
at
address
hex
0091.
Diagnostic
and
automatic
configuration
programs
use
this
signal
to
verify
the
operation
of
an
adapter
at
a
given
address
or
DMA
port.
This
signal
must
not
be
active
during
a
setup
cycle.
The
Card
Selected
Feedback
register
is
a
read-only
register
at
address
hex
0091.
It
allows
programs
to
monitor
-CD
SFDBK
and
thereby
determine
if
the
video
subsystem,
system
board
1/0,
or
an
adapter
is
addressed
and
functioning.
Bit Function
7-1 Reserved
0 -Card Selected Feedback
Figure
2-2.
Card
Selected
Feedback
Register
(Hex
0091)
Bits 7-1 Reserved.
Bit
0
This
bit
is
set
to
1
whenever
-CD
SFDBK
was
active
ona
previous
cycle
or
whenever
the
system
board
I/O
functions
(diskette
drive,
serial,
or
parallel
interfaces)
are
accessed
by
an
I/O
cycle.
Reading
this
register
resets
the
bit
to
0.
System Board Setup
The
integrated
I/O
functions
on
the
system
board
use
POS
information
during
setup.
The
diskette
drive
controller,
serial
port,
and
parailel
port
are
treated
as
a
single
device.
The
video
subsystem
is
also
an
integrated
part
of
the
system
board;
however,
POS
treats
it
as
a
separate
device.
The
System
Board
Enable/Setup
register
is
used
to
place
the
system
board
or
video
subsystem
into
the
setup
mode.
2-6 Model 50 POS — October 1990

IBM Personal System/2 50 Specifications

General

Brand	IBM
Model	Personal System/2 50
Category	Desktop
Language	English