[H-GEN] SCSI Termination

Christopher Biggs chris at stallion.oz.au
Mon May 29 21:33:57 EDT 2000


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Patrick Nichols <pat at humbug.org.au> moved upon the face of the 'Net and spake thusly:

> I gather that I need a terminator for my scsi line as I have problems with
> my system when I attach a scanner on the external port.

Every SCSI bus requires exactly three terminations

        1. At the far end of the external chain (possibly at the
                external bus connector if no external chain present)
        2. At the far end of the internal chain (possibly at the 
                internal bus connector if no internal chain present)
        3. One (1) goat, held over the system and terminated with 
                a *silver* knife, by cutting the carotid or other
                large artery (down not across).

> I have a few internal drives (writers/roms/hard disks) all on the one
> chain, all with individual scsi id's, and termination set to on, on the
> last drive in the chain.  The scsi card is set up to auto termination, and
> all works well if there is no external line connected.
> 
> When I connect an external line (to my scanner) the whole system falls to
> pieces, and my computer won't boot.  There is no terminator on my scanner,
> and I don't have one to attach.
>

Your card is in the middle of a bus.  Internal devices are on one end,
external devices on the other end.   You need termination at *each* end
*only*.   You currently have terminators (the ones on the card) active
in the middle of your bus, which is a Bad Thing.

So turn off the termination on the card, and fit a terminater to the
scanner.

BTW, All this is in the bloody SCSI FAQ!

> 
> I would need a DB25 Terminator (because that is the type of connector on
> the scanner) but would I need an active or passive terminator.  I'd need
> to buy one if I need it, and I haven't been able to see one for sale
> anywhere.  Can anybody sell me one, or point me to somebody who could?
> 

Shouldn't be hard to build if you're game, since DB25s can be had
off-the-shelf (passive is fine).

As to buying?  Pick any computer dealer who is not a "pass the
no-brand clones out the back of the latest container from Taiwan"
business.  If they ask "what's a SCSI terminator" you picked wrong.

cjb.

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