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Chapter 8 BIOS ROM
Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Third Edition - September 1998
8-16
8.4.8 ACCESSING CMOS
Configuration memory data can be retrieved with the BIOS call INT 15, AX=E823h. This tri-
modal function retrieves a single byte from the CMOS map described in Chapter 4. The function
is described as follows:
INPUT:
EAX = E823h
BH = 0, Read
= 1, Write
BL = Value to write (if a write is specified)
CX = Bytes number (zero-based)
OUTPUT:
(Successful)
CF = 0
AH = 00h
AL = Byte value (on a read)
(Failure)
CF = 1
AH = 86h, Function not supported
= FFh, byte does not exist
8.4.9 ACCESSING CMOS FEATURE BITS
The BIOS function INT 15, AX=E845h is a tri-modal call for accessing areas in non-volatile
memory (CMOS) used for storing variables for various features. Note that this function differs
from the previously discussed call since data blocks of varying lengths are retrieved.
INPUT:
EAX = E845h
BL = 0, Read
= 1, Write
BH = Value Read/to Write
CX = Feature Bits Number (refer to following description box)
DS:SI = Pointer to buffer passing multiple byte features
OUTPUT:
(Successful)
CF = 0
EAX = Reserved
BH = Value read (on a read)
(Failure)
CF = 1
AH = 86h, Function not supported