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Amiga Technical References

Commodore A4091 SCSI Adaptor

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 :)

Features

• 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

• 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 termination.
    
  • 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 that.
    
  • 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.
    

Copyright © 2000 Amiga Auckland Inc. All rights reserved.
Revised: June 16, 2005.