HP Vectra Technical Reference Manual page 23

Calling EX-BIOS Drivers
As with the STD-BIOS drivers, each EX-BIOS driver may support one or more functions. A
function code placed in the AH register selects the desired function within the driver. In addition,
a subfunction code passed in the AL register is required by many EX-BIOS functions.
The following program example demonstrates access to a typical EX-BIOS driver. The function
executes a 'beep' on the speaker.
MOV
MOV
PUSH
INT
POP
AH,3AH
BP, 12H
OS
6FH
OS
,. Function: F_SNOJEEP
,. Driver Name: V_SYSTEM
I
,. EX-BIOS Call: HP _ENTRY
On leaving the EX-BIOS driver the BP and DS registers will be modified while the AH register
usually contains the return status of the driver call.
2.3.3 EX-BIOS Standard Functions
Many EX-BIOS drivers support a standard set of functions and subfunctions as listed in table 2.2.
While these functions and subfunctions are defined, it is not required that they all be
implemented by every driver. In addition, EX-BIOS drivers may implement functions other than
those listed. Most EX-BIOS drivers use a standard set of return status codes reported in the AH
register at the completion of a driver's function call. Some of these return status codes and their
definitions are listed in table 2.3. A driver may report a return status code of
RS_UNSUPPORTED (02H) for a given function.
Function codes and return statuses are described in detail in Appendix G.
14 ROM BIOS Overview