Everything You Always Wanted To
But Were Too Polite To Ask
Amiga Technical References
Commodore A4091 SCSI Adaptor
This page was added specifically because so many people appear not to actually
have any documentation on the 4091. I know, because I'm the one who had to
answer all the queries in #amiga on IRC :) The 4091 was licensed to DKB who
built it for a while as well. This documentation refers specifically to the
Commodore version as I'm not sure what changes DKB made to the design (if any.)
I'm trying not to break any copyright with Commodore's original
documentation, but I do need to try to get the information across, so give me
some leeway if I stray :)
- Full Zorro III support
- SCSI-2 support
- Internal 50 pin SCSI connection
- External High density SCSI Connector (aka Mini-D 50)
- Direct Memory Access (DMA) for fast transfers
- Mounting support for 3.5" harddrive on the card
- Board's SCSI Address (Switches 1,2,3)
- ID 0 -- 1 ON ; 2 ON ; 3 ON
- ID 1 -- 1 OFF; 2 ON ; 3 ON
- ID 2 -- 1 ON ; 2 OFF; 3 ON
- ID 3 -- 1 OFF; 2 OFF; 3 ON
- ID 4 -- 1 ON ; 2 ON ; 3 OFF
- ID 5 -- 1 OFF; 2 ON ; 3 OFF
- ID 6 -- 1 ON ; 2 OFF; 3 OFF
- ID 7 -- 1 OFF; 2 OFF; 3 OFF (Default)
- SCSI Fast Bus (Switch 4)
- OFF = SCSI Fast Bus enabled.
- ON = SCSI Fast Bus disabled. Set this if none of the devices on the
SCSI chain support SCSI Fast Bus.
- Short/Long Spinup (Switch 5)
- OFF = System uses standard spinup booting time
- ON = System uses longer booting period. Set this if one of the SCSI
devices is not recognised under a shorter booting period.
- Syncronous Mode (Switch 6)
- OFF = Mode is enabled. This means that not evey byte sent over the
SCSI bus is acknowledged leading to improved response times.
- ON = Mode is disabled.
- External Termination (Switch 7)
- OFF = Termination is turned ON. This means you do not have any
external SCSI devices.
- ON = Termination off. This means you do have external devices and the
last one must be terminated.
- Logical Unit (LUN) Enable (Switch 8)
- OFF = Unit 0 is the only unit recognised.
- ON = Units 1-6 are now recognised. This is essential is you have a
multiple unit device in your SCSI bus such as a CD-ROM jukebox.
Otherwise only the first CD will be recognised.
1 Ground 26 /DB(0)
2 Ground 27 /DB(1)
3 Ground 28 /DB(2)
4 Ground 29 /DB(3)
5 Ground 30 /DB(4)
6 Ground 31 /DB(5)
7 Ground 32 /DB(6)
8 Ground 33 /DB(7)
9 Ground 34 /DB(P)
10 Ground 35 Ground
11 Ground 36 Ground
12 Reserved 37 Reserved
13 Open 38 TERMPWR
14 Reserved 39 Reserved
15 Ground 40 Ground
16 Ground 41 /ATN
17 Ground 42 Ground
18 Ground 43 /BSY
19 Ground 44 /ACK
20 Ground 45 /RST
21 Ground 46 /MSG
22 Ground 47 /SEL
23 Ground 48 /C/D
24 Ground 49 /REQ
25 Ground 50 /I/O
The most recent ROM is 40.13. Thanks to Paul
Reeves of Asimware Innovations for
- What's the device name for the 4091?
- 2nd.scsi.device -- Make sure you type it exactly.
- Why isn't it in DEVS:?
- It's ROM based. This means that the machine can boot off a drive
installed on the 4091. If it was a disk file, you'd have to load it from
disk first. But since you don't have a harddisk since the 4091 isn't
recognised yet, you'd have to boot from floppy (or the internal IDE
drive...if you still have one!)
- Which way in does the external connector go?
- Sensibly enough, there's only one way it will fit physically, and
that's the correct way. But for those who really want to know, looking
from the back on the 4000, pin 1 is on the top left corner where the
housing is widest. Pin 25 is on the top right, pin 26 in on the bottom
left, and pin 50 is on the bottom right.
- System has a nasty habit of hanging on disk accesses.
- You've not terminated the bus correctly. Check to see if you have used
either the internal terminator supplied with the 4091 or that the last
internal device has its own termination set. Then check the external
- Check your cabling. Bad cabling causes more SCSI problems than just
about any other cause and it's a pain to track down until you realise
- Ensure that you don't have any SCSI ID conflicts.
- You have more than one Zorro 3 DMA device (such as a Cybervision 64).
If possible, put that other device into a slow mode.
- The 4091 doesn't like my machine.
- You are using an Amiga 4000 aren't you? Using the 4091 with the 3000
is possible, but not recommended.
- Make sure you have the Rev 11 Buster chip (if you're facing the 4000
from the front, it's to the left of the slots about half way to the back
of the machine. The suffix should be -11. If it isn't, try to find a
replacement from one of the parts companies.
Data not available. I've not opened up the 4000 recently to look at the
names on the PCB :)
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Copyright © 2000 Amiga Auckland Inc. All rights reserved.
Revised: June 16, 2005.