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Chapter 7 BIOS ROM
7.5.1 SYSTEM ID AND ROM TYPE
Applications can use the INT 15, AX=E800h BIOS function to identify the type of system. This
function will return the system ID in the BX register. These systems have the following IDs and
ROM family types:
System System ID ROM Family PnP ID
Small Form Factor
SDR SDRAM
DDR SDRAM
788h
78Ch
686Y2
686Y2
CPQ0042
CPQ0042
Desktop
SDR SDRAM
DDR SDRAM
77Ch
784h
686Y2
686Y2
CPQ003E
CPQ0040
Configurable Minitower
SDR SDRAM
DDR SDRAM
77Ch
784h
686Y2
686Y2
CPQ003F
CPQ0041
The ROM family and version numbers can be verified with the Setup utility or the Compaq
Insight Manager or Diagnostics applications.
7.5.2 EDID RETRIEVE
The BIOS function INT 15, AX=E813h is a tri-modal call that retrieves the VESA extended
display identification data (EDID). Two subfunctions are provided: AX=E813h BH=00h retrieves
the EDID information while AX=E813h BX=01h determines the level of DDC support.
Input:
AX = E813h
BH = 00 Get EDID .
BH = 01 Get DDC support level
If BH = 00 then
DS:(E)SI = Pointer to a buffer (128 bytes) where ROM will return block
If 32-bit protected mode then
DS:(E)SI = Pointer to $DDC location
Output:
(Successful)
If BH = 0:
DS:SI=Buffer with EDID file.
CX = Number of bytes written
CF = 0
AH =00h Completion of command
If BH = 1:
BH = System DDC support
<0>=1 DDC1 support
<1>=1 DDC2 support
BL = Monitor DDC support
<0>=1 DDC1 support
<1>=1 DDC2 support
<2>=1 Screen blanked during transfer
(Failure)
CF = 1
AH = 86h or 87h
Compaq Evo and Workstation Personal Computers
Featuring the Intel Pentium 4 Processor
Second Edition - January 2003
7-14