Accessing Configuration Memory; Accessing Cmos; Setting Default Parameters - Compaq Deskpro 4000N Technical Reference Manual

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.

ACCESSING CMOS

8.3.1
For accessing CMOS bytes, the calling application should use INT 15 AX=E823h, which is
described as follows:
INPUT:
EAX
BH
BL
CX
OUTPUT:
(Successful)
CF
AH
AL
(Failure)
CF
AH
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:
= E823h
= 0, read
= 1, write
= Value to write (if a write is specified)
= Byte number (zero-based)
= 0
= 00h
= Byte Value (if a read was specified)
= 1
= 86h, Function not supported
= FFh, Byte does not exist
Compaq Deskpro 4000N and 4000S Personal Computers
First Edition - September 1997
Technical Reference Guide
8-3