Specifications

Software Configuration
3–29
3.12 SCSI CONTROLLER
The SCSI controller can serve many purposes, including controlling hard disk drives, tape drives, text
scanners, and printer and communications servers. The ROM BIOS supports booting DOS from a SCSI
device such as a hard disk. With Ampro’s ROM BIOS support, you can use any device compatible with
the SCSI Common Command Set for “direct access devices.”
The Little Board/486i Development Kit comes with a diskette containing an assortment of SCSI utilities
for use with DOS. It includes a SCSI hard disk formatting utility that allows low-level formatting and
changing the disk interleaving. Refer to the Ampro Utilities manual for details about using the SCSI
utilities.
Older versions of PC-DOS, for instance Version 3.x, requires you to divide drives larger than 32M bytes
into multiple partitions. Under PC-DOS or MS-DOS 3.x, you can logically divide each drive into as many
as four partitions of 32 megabytes each or smaller, allowing you to use drives as large as 128 megabytes.
More recent versions of MS-DOS remove these restrictions. The Ampro SCSI Common Command Set
implementation puts no realistic limit on drive size (1.8T bytes).
Besides direct access, SCSI devices include sequential access devices (tape), printer devices, read-only
devices (CD-ROM), and processor devices (CPUs). These device types require special application
programs, utilities, or driver software not included on the Ampro Utility diskette.
Hard disk support for operating systems other than DOS may or may not be available through the ROM
BIOS hard disk driver. This depends on two things: whether the operating system in question uses ROM-
BIOS calls exclusively for the hard disk function; and whether the operating system has any special ROM
BIOS constraints, such as reentrancy. Some operating systems—multitasking ones in particular such as
UNIX—bypass the BIOS and attempt to program the hard disk controller directly. With such systems, you
must modify the operating system to add an appropriate SCSI hard disk driver that can take advantage of
the SCSI interface. An alternative is to use the IDE interface instead of SCSI, as the IDE drive standard
is more widely supported.
3.12.1 The Ampro SCSI BIOS
You can use a variety of mass storage devices with the SCSI universal bus interface and command
protocols. Ampro has added a further layer of universality, the SCSI BIOS.
The SCSI BIOS, a set of low level functions in the ROM BIOS, is a hardware-independent interface
between system software and SCSI peripherals. The advantage of the Ampro SCSI BIOS is in interfacing
to devices. Programmers can write software for SCSI devices without concern for the operational details
of the SCSI interface. Also, the SCSI BIOS enables you to import software from other environments more
safely, quickly, and easily.
Application Note AAN-8804, available from Ampro, provides details of the SCSI BIOS functions.
3.12.2 SCSI Drive Preparation for DOS Use
To use a hard disk drive on the SCSI port, you must properly connect and jumper it, set the appropriate
parameters in SETUP, and then format the drive for use with DOS.
Here is a procedure you can use to prepare (format and partition) a SCSI hard disk drive for use
with DOS:
1. Set the SCSI Device IDs—using the options in SETUP’s Extended SCSI and Hard Disk
Configuration menu, specify the appropriate SCSI device IDs for both the drive and the Little
Board/486i. This ID must match jumpers on the drive. If you set the SCSI controller on the CPU
board to SCSI ID 7, a SCSI bus Reset command will be issued on system powerup or system reset.