| Offset
Hex |
Offset
Dec |
Field
Size |
Function |
|
00h
|
0 |
1
byte |
RTC
seconds. Contains the seconds value of current time |
| 01h |
1 |
1
byte |
RTC
seconds alarm. Contains the seconds value for the RTC
alarm |
| 02h |
2 |
1
byte |
RTC
minutes. Contains the minutes value of the current
time |
| 03h |
3 |
1
byte |
RTC
minutes alarm. Contains the minutes value for the RTC
alarm |
| 04h |
4 |
1
byte |
RTC
hours. Contains the hours value of the current time |
| 05h |
5 |
1
byte |
RTC
hours alarm. Contains the hours value for the RTC alarm |
| 06h |
6 |
1
byte |
RTC
day of week. Contains the current day of the week |
| 07h |
7 |
1
byte |
RTC
date day. Contains day value of current date |
| 08h |
8 |
1
byte |
RTC
date month. Contains the month value of current date |
| 09h |
9 |
1
byte |
RTC
date year. Contains the year value of current date |
| 0Ah |
10 |
1
byte |
Status
Register A |
| |
|
|
Bit 7 = Update
in progress (0 = Date and time can be read, 1 = Time update in progress) |
| |
|
|
Bits 6-4
= Time frequency divider (010 = 32.768KHz |
| |
|
|
Bits 3-0
= Rate selection frequency (0110 = 1.024KHz square wave frequency) |
| 0Bh |
11 |
1
byte |
Status
Register B |
| |
|
|
Bit 7 = Clock
update cycle (0 = Update normally, 1 = Abort update in progress) |
| |
|
|
Bit 6 = Periodic
interrupt (0 = Disable interrupt (default), 1 = Enable interrupt)
|
| |
|
|
Bit 5 = Alarm
interrupt (0 = Disable interrupt (default), 1 = Enable interrupt) |
| |
|
|
Bit 4 = Update
ended interrupt (0 = Disable interrupt (default), 1 = Enable interrupt) |
| |
|
|
Bit 3 = Status
register A square wave frequency (0 = Disable square wave (default),
1 = Enable square wave) |
| |
|
|
Bit 2 = 24
hour clock (0 = 24 hour mode (default), 1 = 12 hour mode) |
| |
|
|
Bit 1 = Daylight
savings time (0 = Disable daylight savings (default), 1 = Enable
daylight savings) |
| 0Ch |
12 |
1
byte |
Status
Register C - Read only flags indicating system status conditions |
| |
|
|
Bit 7 = IRQF
flag |
| |
|
|
Bit 6 = PF
flag |
| |
|
|
Bit 5 = AF
flag |
| |
|
|
Bit 4 UF
flag |
| |
|
|
Bits 3-0
= Reserved |
| 0Dh |
13 |
1
byte |
Status
Register D - Valid CMOS RAM flag on bit 7 (battery condition
flag) |
| |
|
|
Bit 7 = Valid
CMOS RAM flag (0 = CMOS battery dead, 1 = CMOS battery power good) |
| |
|
|
Bit 6-0 =
Reserved |
| 0Eh |
14 |
1
byte |
Diagnostic
Status |
| |
|
|
Bit 7 = Real
time clock power status (0 = CMOS has not lost power, 1 = CMOS has
lost power) |
| |
|
|
Bit 6 = CMOS
checksum status (0 = Checksum is good, 1 = Checksum is bad) |
| |
|
|
Bit 5 = POST
configuration information status (0 = Configuration information
is valid, 1 = Configuration information in invalid) |
| |
|
|
Bit 4 = Memory
size compare during POST (0 = POST memory equals configuration,
1 = POST memory not equal to configuration) |
| |
|
|
Bit 3 = Fixed
disk/adapter initialization (0 = Initialization good, 1 = Initialization
bad) |
| |
|
|
Bit 2 = CMOS
time status indicator (0 = Time is valid, 1 = Time is invalid) |
| |
|
|
Bit 1-0 =
Reserved |
| 0Fh |
15 |
1
byte |
CMOS
Shutdown Status |
| |
|
|
00h = Power
on or soft reset |
| |
|
|
01h = Memory
size pass |
| |
|
|
02h = Memory
test pass |
| |
|
|
03h = Memory
test fail |
| |
|
|
04h = POST
complete; boot system |
| |
|
|
05h = JMP
double word pointer with EOI |
| |
|
|
06h = Protected
mode tests pass |
| |
|
|
07h = protected
mode tests fail |
| |
|
|
08h = Memory
size fail |
| |
|
|
09h = Int
15h block move |
| |
|
|
0Ah = JMP
double word pointer without EOI |
| |
|
|
0Bh = Used
by 80386 |
| 10h |
16 |
1
byte |
Floppy
Disk Drive Types |
| |
|
|
Bits 7-4
= Drive 0 type |
| |
|
|
Bits 3-0
= Drive 1 type |
| |
|
|
0000 = None |
| |
|
|
0001 = 360KB |
| |
|
|
0010 = 1.2MB |
| |
|
|
0011 = 720KB |
| |
|
|
0100 = 1.44MB |
| 11h |
17 |
1
byte |
System
Configuration Settings |
| |
|
|
Bit 7 = Mouse
support disable/enable |
| |
|
|
Bit 6 = Memory
test above 1MB disable/enable |
| |
|
|
Bit 5 = Memory
test tick sound disable/enable |
| |
|
|
Bit 4 = Memory
parity error check disable/enable |
| |
|
|
Bit 3 = Setup
utility trigger display disable/enable |
| |
|
|
Bit 2 = Hard
disk type 47 RAM area (0:300h or upper 1KB of DOS area) |
| |
|
|
Bit 1 = Wait
for <F1> if any error message disable/enable |
| |
|
|
Bit 0 = System
boot up with Numlock (off/on) |
| 12h |
18 |
1
byte |
Hard
Disk Types |
| |
|
|
Bits 7-4
= Hard disk 0 type |
| |
|
|
Bits 3-0
= Hard disk 1 type |
| |
|
|
0000 = No
drive installed |
| |
|
|
0001 = Type
1 installed |
| |
|
|
1110 = Type
14 installed |
| |
|
|
1111 = Type
16-47 (defined later in 19h) |
| 13h |
19 |
1
byte |
Typematic
Parameters |
| |
|
|
Bit 7 = typematic
rate programming disable/enabled |
| |
|
|
Bit 6-5 =
typematic rate delay |
| |
|
|
Bit 4-2 =
Typematic rate |
| 14h |
20 |
1
byte |
Installed
Equipment |
| |
|
|
Bits 7-6
= Number of floppy disks (00 = 1 floppy disk, 01 = 2 floppy disks) |
| |
|
|
Bits 5-4
= Primary display (00 = Use display adapter BIOS, 01 = CGA 40 column,
10 = CGA 80 column, 11 = Monochrome Display Adapter) |
| |
|
|
Bit 3 = Display
adapter installed/not installed |
| |
|
|
Bit 2 = Keyboard
installed/not installed |
| |
|
|
Bit 1 = math
coprocessor installed/not installed |
| |
|
|
Bit 0 = Always
set to 1 |
| 15h
|
21 |
1
byte |
Base
Memory Low Order Byte - Least significant byte |
| 16h |
22 |
1
byte |
Base
Memory High Order Byte - Most significant byte |
| 17h |
23 |
1
byte |
Extended
Memory Low Order Byte - Least significant byte |
| 18h |
24 |
1
byte |
Extended
Memory High Order Byte - Most significant byte |
| 19h |
25 |
1
byte |
Hard
Disk 0 Extended Type - (10h to 2Eh = Type 16 to 46 respectively) |
| 1Ah |
26 |
1
byte |
Hard
Disk 1 Extended Type - (10h to 2Eh = Type 16 to 46 respectively) |
| 1Bh |
27 |
1
byte |
User
Defined Drive C: - Number of cylinders least significant
byte |
| 1Ch |
28 |
1
byte |
User
Defined Drive C: - Number of cylinders most significant byte |
| 1Dh |
29 |
1
byte |
User
Defined Drive C: - Number of heads |
| 1Eh |
30 |
1
byte |
User
Defined Drive C: - Write precomp cylinder least significant
byte |
| 1Fh |
31 |
1
byte |
User
Defined Drive C: - Write precomp cylinder most significant
byte |
| 20h |
32 |
1
byte |
User
Defined Drive C: - Control byte |
| 21h |
33 |
1
byte |
User
Defined Drive C: - Landing zone least significant byte |
| 22h |
34 |
1
byte |
User
Defined Drive C: - Landing zone most significant byte |
| 23h |
35 |
1
byte |
User
Defined Drive C: - Number of sectors |
| 24h |
36 |
1
byte |
User
Defined Drive D: - Number of cylinders least significant
byte |
| 25h |
37 |
1
byte |
User
defined Drive D: - Number of cylinders most significant byte |
| 26h |
38 |
1
byte |
User
Defined Drive D: - Number of heads |
| 27h |
39 |
1
byte |
User
Defined Drive D: - Write precomp cylinder least significant
byte |
| 28h |
40 |
1
byte |
User
Defined Drive D: - Write precomp cylinder most significant
byte |
| 29h |
41 |
1
byte |
User
Defined Drive D: - Control byte |
| 2Ah |
42 |
1
byte |
User
Defined Drive D: - Landing zone least significant byte |
| 2Bh |
43 |
1
byte |
User
Defined Drive D: - Landing zone most significant byte |
| 2Ch |
44 |
1
byte |
User
Defined Drive D: - Number of sectors |
| 2Dh |
45 |
1
byte |
System
Operational Flags |
| |
|
|
Bit 7 = Weitek
processor present/absent |
| |
|
|
Bit 6 = Floppy
drive seek at boot enable/disable |
| |
|
|
Bit 5 = System
boot sequence |
| |
|
|
Bit 4 = System
boot CPU speed high/low |
| |
|
|
Bit 3 = External
cache enable/disable |
| |
|
|
Bit 2 = Internal
cache enable/disable |
| |
|
|
Bit 1 = Fast
gate A20 operation enable/disable |
| |
|
|
Bit 0 = Turbo
switch function enable/disable |
| 2Eh |
46 |
1
byte |
CMOS
Checksum High Order Byte - Most significant byte |
| 2Fh |
47 |
1
byte |
CMOS
Checksum Low Order Byte - Least significant byte |
| 30h |
48 |
1
byte |
Actual
Extended Memory Low Order Byte - Least significant byte |
| 31h |
49 |
1
byte |
Actual
Extended Memory High Order Byte - Most significant byte |
| 32h |
50 |
1
byte |
Century
Date BCD - Value for century of current date |
| 33h |
51 |
1
byte |
POST
Information Flags |
| |
|
|
Bit 7 = BIOS
length (64KB/128KB) |
| |
|
|
Bit 6-1 =
reserved |
| |
|
|
Bit 0 = POST
cache test passed/failed |
| 34h |
52 |
1
byte |
BIOS
and Shadow Option Flags |
| |
|
|
Bit 7 = Boot
sector virus protection disabled/enabled |
| |
|
|
Bit 6 = Password
checking option disabled/enabled |
| |
|
|
Bit 5 = Adapter
ROM shadow C800h (16KB) disabled/enabled |
| |
|
|
Bit 4 = Adapter
ROM shadow CC00h (16KB) disabled/enabled |
| |
|
|
Bit 3 = Adapter
ROM shadow D000h (16KB) disabled/enabled |
| |
|
|
Bit 2 = Adapter
ROM shadow D400h (16KB) disabled/enabled |
| |
|
|
Bit 1 = Adapter
ROM shadow D800h (16KB) disabled/enabled |
| |
|
|
Bit 0 = Adapter
ROM shadow DC00h (16KB) disabled/enabled |
| 35h |
53 |
1
byte |
BIOS
and Shadow Option Flags |
| |
|
|
Bit 7 = Adapter
ROM shadow E000h (16KB) disabled/enabled |
| |
|
|
Bit 6 = Adapter
ROM shadow E400h (16KB) disabled/enabled |
| |
|
|
Bit 5 = Adapter
ROM shadow E800h (16KB) disabled/enabled |
| |
|
|
Bit 4 = Adapter
ROM shadow EC00h (16KB) disabled/enabled |
| |
|
|
Bit 3 = System
ROM shadow F000h (16KB) disabled/enabled |
| |
|
|
Bit 2 = Video
ROM shadow C000h (16KB) disabled/enabled |
| |
|
|
Bit 1 = Video
ROM shadow C400h (16KB) disabled/enabled |
| |
|
|
Bit 0 = Numeric
processor test disabled/enabled |
| 36h |
54 |
1
byte |
Chipset
Specific Information |
| 37h |
55 |
1
byte |
Password
Seed and Color Option |
| |
|
|
Bit 7-4 =
Password seed (do not change) |
| |
|
|
Bit 3-0 =
Setup screen color palette |
| |
|
|
07h = White
on black |
| |
|
|
70h = Black
on white |
| |
|
|
17h = White
on blue |
| |
|
|
20h = Black
on green |
| |
|
|
30h = Black
on turquoise |
| |
|
|
47h = White
on red |
| |
|
|
57h = White
on magenta |
| |
|
|
60h = Black
on brown |
| 38h-3dh |
56-61 |
6
bytes |
Encrypted
Password - (do not change) |
| 3Eh |
62 |
1
byte |
Extended
CMOS Checksum - Most significant byte |
| 3Fh |
63 |
1
byte |
Extended
CMOS Checksum - Least significant byte |
| 40h |
64 |
1
byte |
Model
Number Byte |
| 41h |
65 |
1
byte |
1st
Serial Number Byte |
| 42h |
66 |
1
byte |
2nd
Serial Number Byte |
| 43h |
67 |
1
byte |
3rd
Serial Number Byte |
| 44h |
68 |
1
byte |
4th
Serial Number Byte |
| 45h |
69 |
1
byte |
5th
Serial Number Byte |
| 46h |
70 |
1
byte |
6th
Serial Number Byte |
| 47h |
71 |
1
byte |
CRC
Byte |
| 48h |
72 |
1
byte |
Century
Byte |
| 49h |
73 |
1
byte |
Date
Alarm |
| 4Ah |
74 |
1
byte |
Extended
Control Register 4A |
| 4Bh |
75 |
1
byte |
Extended
Control register 4B |
| 4Ch |
76 |
1
byte |
Reserved |
| 4Dh |
77 |
1
byte |
Reserved |
| 4Eh |
78 |
1
byte |
Real
Time Clock - Address 2 |
| 4Fh |
79 |
1
byte |
Real
Time Clock - Address 3 |
| 50h |
80 |
1
byte |
Extended
RAM Address - Least significant byte |
| 51h |
81 |
1
byte |
Extended
RAM Address - Most significant byte |
| 52h |
82 |
1
byte |
Reserved |
| 53h |
83 |
1
byte |
Extended
RAM Data Port |
| 54h |
84 |
1
byte |
Reserved |
| 55h |
85 |
1
byte |
Reserved |
| 56h |
86 |
1
byte |
Reserved |
| 57h |
87 |
1
byte |
Reserved |
| 58h |
88 |
1
byte |
Reserved |
| 59h |
89 |
1
byte |
Reserved |
| 5Ah |
90 |
1
byte |
Reserved |
| 5Bh |
91 |
1
byte |
Reserved |
| 5Ch |
92 |
1
byte |
Reserved |
| 5Dh |
93 |
1
byte |
Reserved |
