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Technical Reference Guide
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
8-3
8.3 ACCESSING CONFIGURATION MEMORY
Configuration memory (CMOS and NVRAM) should be accessed using the appropriate BIOS
function. The following subsections describe several BIOS functions available to applications for
accessing the system’s non-volatile memory.
8.3.1
ACCESSING CMOS
For accessing CMOS bytes, the calling application should use INT 15 AX=E823h, which is
described as follows:
INPUT:
EAX = E823h
BH = 0, read
= 1, write
BL = Value to write (if a write is specified)
CX = Byte number (zero-based)
OUTPUT:
(Successful)
CF = 0
AH = 00h
AL = Byte Value (if a read was specified)
(Failure)
CF = 1
AH = 86h, Function not supported
= FFh, Byte does not exist
8.3.2
SETTING DEFAULT PARAMETERS
The BIOS function INT 15, AX=E841h is used for setting various system parameters to the
default settings on the next system boot. This function is intended for Plug ‘n Play (PnP) support
(refer to section 8.5 “Plug ‘n Play” for more information. Two variances of the function are
available and described as follows: