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SCSI Interface
~~~~~~~~~~~~~~
The A3000 benefits from a DMA SCSI adapter, based around the
Western Digital WDC33C93 Narrow SCSI1 chip.  It can accomodate a variety of
peripherals and storage, including SCSI flatbed scanners, CDRoms, and hard
disks.  An A3000's hard disk is usually interfaced through the SCSI port.
While there are two physical ports, a 50 pin header connector internally,
and a DB25 Macintosh Plus style port externally, it is the same bus
electrically.

The A3000 should be interfaced in the following manner:

    ------       |  ------        ------
T--|extdev|--...-+-| SCSI |-...--|intdev|---T
    ------       |  ------        ------

Devices are placed in daisychain fashion, with cables going both
externally and internally.  However somewhere on this chain, the SCSI
adapter is present.  

See also, Warren Block's SCSI Examples guide

Other good sources of information are:
SCSIFAQ.org


ID Numbers
~~~~~~~~~~
It is generally recommended to put removable drives like CDRom and
Syquests with a higher ID number.  The adapter itself is Unit 7.  This is
adjustable using various NVRAM settings.  

See also, See also, Jumpers for how to set
NVRAM options.
 
Cabling
~~~~~~~
Cabling should follow SCSI specifications.  In general, most
cables, as long as the drive follows the right specification, should work.
For external devices, you'll want to get a DB25 male connector on the Amiga
system end, for internal, 50 pin header.  

Termination
~~~~~~~~~~~
As with any SCSI bus, both ends of the chain must be
terminated.  Depending on the configuration, and owner, the A3000
motherboard may or may not be terminated.  If it is, and you want external
devices, you should remove motherboard termination.  If not, leave it on.
The end of the internal drive chain should be terminated.  The internal
terminators are at RP802, RP803, and RP804.

If you have removed motherboard termination, make sure the last
external device is terminated. This could be inside your drive
enclosure, or on the end of a passthrough connector.  Usually the Amiga
supplies power for termination.  Remember to check your documentation for
determining which device needs to supply termpower.

See also, SCSI-Termination Power

Some users suggest using active termination both internally and
externally.  Many SCSI issues are fixed with the Rev -08 SCSI chip, as
well as the AMD compatible replacements.  These can be sourced in the UK
from Tim Corringham, RamJam, UK phone 0118 946 5940, at £26.50.  Depending
on your system and your devices, replacement of the 33C93 can solve or
create problems.  It really depends on your specific configuration.

Types of SCSI
~~~~~~~~~~~~~
Differential SCSI - Will not work with A3000.  Requires Narrow to
    Differential adapter.  May as well buy new drive.
    Often used in Sun and IBM RS/6000 workstations.

Wide SCSI  - Will work with A3000, but requires adapter
    plug that is relatively pricey and hard to
    find.

     SCSI2  - Will work with A3000.  SCSI2 is a superset of
    commands of SCSI1.

Fast SCSI2  - Will work, but not at full speed.

SCSI3  - Should work with A3000.

UltraSCSI  - Brand name for SCSI3, should work.

FireWire DV1394   - Will not work.  Completely different standard,
    it's not SCSI at all.  Apple Macintosh users
    often confuse FireWire with SCSI3.  Used
    in the Sony DCR-VX1000 6mm Digital cameras
    for transfer of motion video and sound.

USB   - Will not work.  Another different standard,
    not SCSI at all.  Often confused with 1394,
    which is confused with SCSI.  Universal
    Serial Bus, new Intel/Windows hardware spec.