IBM XT 5160 Technical Reference page 49

-
- -
Hex
PAO
+
Keyboard Scan Code 0
Diagnostic Outputs 0
Port I
1
1
1
Number N 2 2
2
P
3
3 Or
3
0060 U 4 4 4
T
5 5 5
6
6
6
7 7 7
-
"'"--
-
PBO
+
Timer 2 Gate Speaker
0 1
+
Speaker Data
U
2 Spare
T
3
Read High Switches or Read Low Switches
0061 P 4 - Enable RAM Parity Check
U
5
- Enable I/O Channel Check
T 6 - Hold Keyboard Clock Low
7
- (Enable Keyboard or
+
(Clear Keyboard)
PCO Loop on POST
SW~
[[:SPla
y
0
..I.
Sw-5
I 1
+
CoProcessor Installed Sw-2 Display 1
..I.
Sw-6
N 2
+
Planar RAM Size 0
..I.
Sw-3 Or # Drives
..1...1.
Sw-7
0062 P
3
+
Planar RAM Size 1
..I.
Sw-4 # Drives 1
..1...1.
Sw-8
U 4 Spare
T
5
+
Timer Channel 2 Out
UJJ
+
I/O Channel Check
+
RAM Parity Check
0063 Command/Mode Register Hex 99
Mode Register Value
7 6
5
4
3
2 1 0
1 0 0 1 1 0 0 1
..I.
Sw-4
Sw-3
Amount of Memory on System Board - 64/256K
0 0 64K
0
1
128K
1 0
192K
1 1 256K
..I.
Sw-4
Sw-3 Amount of Memory on System Board - 256/640K
0 0 256K
0
1 512K
1
0
576K
1 1 640K
..1...1.
Sw-6 Sw-5 Display at Power-Up Mode
0
0
Reserved
0
1
Color 40 X 25 (BW Mode)
1 0 Color 80 X 25 (BW Mode)
1
1
IBM Monochrome 80 X 25
..1...1...1.
Sw-8
Sw-7 Number of Diskette Drives in System
0
0 1
0 1 2
1 0
3
1 1 4
Notes:
PA Bit
=
0 implies switch "ON". PA Bit
=
1 implies switch " OFF ".
A plus
(+)
indicates a bit value of 1 performs the specified function.
A minus (-) indicates a bit value of 0 performs the specified function.
8255A I/O Bit Map
1-28 System Board