IBM Personal System/2 50 - System Board POS Register 2 (Hex 0102)

System Board POS Register 2 (Hex 0102)
When
the
system
board
is
in
the
setup
mode,
the
diskette
drive
controller,
serial
port,
and
parallel
port
are
controlled
by
this
read/write
register.
Reading
this
register
returns
the
current
state
of
these
system
board
functions.
Bit Function
7 Disable Parallel Port Extended Mode
6,
OA
NOA
5 Parallel Port Select
Enable Parallel Port
Serial Port Select
Enable Serial Port
Enable Diskette Drive Interface
Enable System Board
Figure
2-4.
System
Board
POS
Register
2
(Hex
0102)
Bit7
When set to 0, this bit allows the parallel port to be
configured as an 8-bit, parallel, bidirectional interface.
When set to 1, this bit disables the bidirectional mode.
This bit is set to 0 at power-on, and POST sets it to 1.
These
bits
select
the
configuration
of
the
system
board
parallel
port.
Bits
65
Assignment
Hex
Address
Interrupt
Level
00 Parallel 1 03BC - 03BF 7
o1 Parallel 2 0378 - 037B 7
10 Parallel 3 0278 - 027B 7
it Reserved cote eeenenennne -
Figure 2-5. Parallel Port Select Bits
Bit 4
Bit 3
2-8
When
this
bit
and
bit
0
are
set
to
1,
the
system
board
parallel
port
is
enabled.
When
set
to
1,
this
bit
sets
the
system
board
serial
port
as
Serial
1
(addresses
hex
03F8
through
03FF),
which
uses
interrupt
level
4.
When
set
to
0,
this
bit
sets
the
serial
port
as
Serial
2
(addresses
hex
02F8
through
02FF),
which
uses
interrupt
level
3.
Model 50 POS — October 1990