Int 15H Functionality; Differences Between Operating Modes - Adaptec AHA-1740A Technical Reference Manual

EISA-to-Fast SCSI Host Adapter
The output of this function is defined as follows:
Register
AH
DL
CX
CF
The following function codes are not supported by the AHA-1740A/1742A BIOS:
(AH) = 05h Format Desired Cylinder
(AH) = 06h Format Desired Cylinder and Set Bad Sector Flags
(AH) = 07h Format Drive Starting at Desired Cylinder
(AH) = 0Ah Reserved
(AH) = 0Bh Reserved
(AH) = 0Eh Reserved
(AH) = 0Fh Reserved
(AH) = 12h Reserved
(AH) = 13h Reserved
(AH) = 14h Reserved
(AH) = 16h Reserved
(AH) = 17h Reserved
(AH) = 18h Reserved
(AH) = 19h Park Heads
(AH) = 1Ah Format Unit
(AH) = 1Bh-FFhReserved
An invalid command error is returned for any of these function codes.

Int 15h Functionality

After issuing an I/O command to the host adapter, the AHA-1740A/1742A BIOS will
make use of the Int 15 Device Busy (function 90h) to inform the operating system
that the BIOS is about to wait for a device.
When the AHA-1740A/1742A interrupts indicating that the I/O is complete, an Inter-
rupt Complete (function 91h) will be issued by the BIOS indicating that the wait is
complete.

Differences Between Operating Modes

VDS is supported in Enhanced Mode only
In EISA mode, the BIOS will scan for Int 13h devices
Onboard BIOS Interface
Function
Status of Operation
00h - Drive not present or invalid DL
03h - Fixed Disk Present
01h, 02h - Reserved
Number of blocks on disk
Return Code
7-9