Cmos Archive And Restore; Standard Cmos Locations - Compaq Deskpro Workstation AP230 Technical Reference Manual

Chapter 4 System Support

4.6.2 CMOS ARCHIVE AND RESTORE

During the boot sequence the BIOS saves a copy of NVRAM (CMOS contents, password(s) and
other system variables) in a portion of the flash ROM. Should the system become un-usable, the
last good copy of NVRAM data can be restored with the Power Button Override function. This
function is invoked with the following procedure:
1. With the unit powered down, press and release the power button.
2. Immediately after releasing the power button in step 1, press and hold the power button until
the unit powers down. This action will be recorded as a Power Button Override event.
With the next startup sequence the BIOS will detect the occurrence of the Power Button Override
event and will load the backup copy of NVRAM from the ROM to the CMOS.
NOTE: The Power Button Override feature does not allow quick cycling of the system
(turning on then off). If the power cord is disconnected during the POST routine, the
splash screen image may become corrupted, requiring a re-flashing of the ROM (refer to
chapter 8, BIOS ROM).

4.6.3 STANDARD CMOS LOCATIONS

Table 4-14 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 4-14. Configuration Memory (CMOS) Map
Location Function
00-0Dh Real-time clock
0Eh Diagnostic status
0Fh System reset code
10h Diskette drive type
11h Reserved
12h Hard drive type
13h Security functions
14h Equipment installed
15h Base memory size, low byte/KB
16h Base memory size, high byte/KB
17h Extended memory, low byte/KB
18h Extended memory, high byte/KB
19h Hard drive 1, primary controller
1Ah Hard drive 2, primary controller
1Bh Hard drive 1, secondary controller
1Ch Hard drive 2, secondary controller
1Dh Enhanced hard drive support
1Eh Reserved
1Fh Power management functions
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).
RTC Control Register A, Byte 0Ah
4-24 Compaq Deskpro Personal Computers
Table 4-14.
Configuration Memory (CMOS) Map
Location
24h
25h
26h
27h
28h
29h
2Ah
2Bh
2Ch
2Dh
2Eh-2Fh
30h-31h
32h
33h
34h
35h
36h
37h-3Fh
40-FFh
Third Edition – April 2001
Function
System board ID
System architecture data
Auxiliary peripheral configuration
Speed control external drive
Expanded/base mem. size, IRQ12
Miscellaneous configuration
Hard drive timeout
System inactivity timeout
Monitor timeout, Num Lock Cntrl
Additional flags
Checksum of locations 10h-2Dh
Total extended memory tested
Century
Miscellaneous flags set by BIOS
International language
APM status flags
ECC POST test single bit
Power-on password
Feature Control/Status