Technical Reference Guide
4.6.2 CMOS ARCHIVE AND RESTORE
During the boot process the BIOS saves a copy of CMOS to the flash ROM. If the system
becomes unusable, the last good copy of CMOS can be recalled using the power-override function
as follows:
1.
With the unit powered down, press and release the power button to initiate the boot sequence.
2.
Immediately after releasing the power button, press it again and hold (typically at least four
seconds) until the unit powers off again. This action will be recorded as a power button
override event.
3.
Press and release the power button once more, initiating the boot sequence that should detect
the occurrence of an override event and load the backup copy of CMOS, allowing the system
to boot.
4.6.3 STANDARD CMOS LOCATIONS
Table 4-11 and the following paragraphs describe standard configuration memory locations 0Ah-
3Fh. These locations are accessible through using OUT/IN assembly language instructions using
port 70/71h or BIOS function INT15, AX=E823h.
Table 4-11. Configuration Memory (CMOS) Map
Table 4-11.
Configuration Memory (CMOS) Map
Location Function
Location
Function
00-0Dh
Real-time clock
24h
System board ID
0Eh
Diagnostic status
25h
System architecture data
0Fh
System reset code
26h
Auxiliary peripheral configuration
10h
Diskette drive type
27h
Speed control external drive
11h
Reserved
28h
Expanded/base mem. size, IRQ12
12h
Hard drive type
29h
Miscellaneous configuration
13h
Security functions
2Ah
Hard drive timeout
14h
Equipment installed
2Bh
System inactivity timeout
15h
Base memory size, low byte/KB
2Ch
Monitor timeout, Num Lock Cntrl
16h
Base memory size, high byte/KB
2Dh
Additional flags
17h
Extended memory, low byte/KB
2Eh-2Fh
Checksum of locations 10h-2Dh
18h
Extended memory, high byte/KB
30h-31h
Total extended memory tested
19h
Hard drive 1, primary controller
32h
Century
1Ah
Hard drive 2, primary controller
33h
Miscellaneous flags set by BIOS
1Bh
Hard drive 1, secondary controller 34h
International
language
1Ch
Hard drive 2, secondary controller
35h
APM status flags
1Dh
Enhanced hard drive support
36h
ECC POST test single bit
1Eh Reserved
37h-3Fh Power-on
password
1Fh
Power management functions
40-FFh
Feature Control/Status
NOTES:
Assume unmarked gaps are reserved.
Higher locations (>3Fh) contain information that should be accessed using the INT15, AX=E845h
BIOS function (refer to Chapter 8 for BIOS function descriptions).
Compaq D315 and hp d325 Personal Computers
Featuring the AMD Athlon XP Processor
Second Edition - April 2003
4-23