Hardware Reference
In-Depth Information
Table 1.14 BIOS data area
Offset
Offset
BIOS
Field size
(hex.)
(dec.)
service
(bytes)
Function
00h
0
Int 14h
2
Base I/O address for serial port 1 (COM 1)
02h
2
Int 14h
2
Base I/O address for serial port 2 (COM 2)
04h
4
Int 14h
2
Base I/O address for serial port 3 (COM 3)
06h
6
Int 14h
2
Base I/O address for serial port 4 (COM 4)
08h
8
Int 17h
2
Base I/O address for parallel port 1 (LPT 1)
0Ah
10
Int 17h
2
Base I/O address for parallel port 2 (LPT 2)
0Ch
12
Int 17h
2
Base I/O address for parallel port 3 (LPT 3)
0Eh
14
POST
2
Base I/O address for parallel port 4 (LPT 4)
10h
16
Int 11h
2
Equipment Word
12h
18
POST
1
Interrupt flag - Manufacturing test
13h
19
Int 12h
2
Memory size in KB
15h
21
2
Error codes for AT; adapter memory size for PC and XT
17h
22
Int 16h
1
Keyboard shift flag 1
18h
23
Int 16h
1
Keyboard shift flag 2
19h
24
Int 09h
1
Alt Num pad work area
1Ah
26
Int 16h
2
Pointer to the address of the next character in the keyboard buffer
1Ch
28
Int 16h
2
Pointer to the address of the last character in the keyboard buffer
1Eh
60
Int 16h
32
Keyboard buffer
3Eh
61
Int 13h
1
Floppy disk drive calibration status
3Fh
62
Int 13h
1
Floppy disk drive motor status
40h
63
Int 13h
1
Floppy disk drive motor time-out
41h
64
Int 13h
1
Floppy disk drive status
42h
65
Int 13h
1
Hard disk and floppy controller Status Register 0
43h
66
Int 13h
1
Floppy drive controller Status Register 1
44h
67
Int 13h
1
Floppy drive controller Status Register 2
45h
68
Int 13h
1
Floppy disk controller: cylinder number
46h
69
Int 13h
1
Floppy disk controller: head number
47h
70
Int 13h
1
Floppy disk controller: sector number
48h
71
1
Floppy disk controller: number of written
49h
72
Int 10h
1
Active video mode setting
4Ah
74
Int 10h
2
Number of text columns per row for the active video mode
4Ch
76
Int 10h
2
Size of active video in page s
4Eh
78
Int 10h
2
Offset address of the active video page relative to the start of video RAM
50h
80
Int 10h
2
Cursor position for video page 0
52h
82
Int 10h
2
Cursor position for video page 1
54h
84
Int 10h
2
Cursor position for video page 2
56h
86
Int 10h
2
Cursor position for video page 3
58h
88
Int 10h
2
Cursor position for video page 4
5Ah
90
Int 10h
2
Cursor position for video page 5
5Ch
92
Int 10h
2
Cursor position for video page 6
5Eh
94
Int 10h
2
Cursor position for video page 7
60h
96
Int 10h
2
Cursor shape
62h
97
Int 10h
1
Active video page
63h
99
Int 10h
2
I/O port address for the video display adapter
65h
100
Int 10h
1
Video display adapter internal mode register
66h
101
Int 10h
1
Colour palette
67h
103
2
Adapter ROM offset address
( continued )
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