HP Vectra Technical Reference Manual page 310

Write a byte to CMOS. Calculate a new checksum for both the industry standard CMOS area and
the HP CMOS area.
On Entry: BP
=
V_SYSTEM (12H)
AH
=
F_CMOS_RET (24H)
AL
=
byte of data to be written to CMOS
BL
=
address of byte to be written to CMOS
On Exit: AH
=
Return Status Code
Registers Altered: AX, BP, DS.
Example: Make the monochrome display the primary video adapter by setting this information in
the equipment byte of CMOS memory.
,
; Read the equipment byte.
MOV
MOV
MOV
PUSH
INT
POP
CMP
JE
BP, V_SYSTEM
AH, F_CMOS_GET
BL, 74H
OS
HP_ENTRY
OS
AH, RS_FAIL
INVALID_CMOS
; HP vector 72H.
; function 22H
; Address of the equipment byte
,. EX-BIOS destroys OS
; Int 6FH for EX-BIOS
; See if CMOS is valid
,
,. Isolate the video and set appropiate video bits.
AND
OR
AL,
7700 7777
B
AL,
007
70000B
" Select monochrome display
Write the equipment byte.
MOV
MOV
PUSH
INT
POP
BP, V_SYSTEM
AH, F_CMOS__RET
OS
HP_ENTRY
OS
; HP vector 72H
,. function 24H
; EX-BIOS destroys OS
,. Int 6FH for EX-BIOS
System Drivers 301