Cable swap blows Ultra2 cards?

Gary Watson gary at trimm.co.uk
Wed Oct 7 09:54:07 PDT 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gary Watson <gary at trimm.co.uk>
*

The host adapter was otherwise disconnected, so it would have been 
defaulted to LVD mode, until the point when a cable from a powered off 
single ended drive expansion cabinet was plugged into it.

Gary Watson			Trimm Technologies Ltd.
Engineering Manager		A Subsidiary of Robroy Industries, Inc.
gary at trimm.co.uk		Nottingham NG8 6AR  ENGLAND
http://www.trimm.co.uk		+44 115 951 9951


-----Original Message-----
From:	Harlan Andrews [SMTP:hea at apple.com]
Sent:	07 October 1998 16:39
To:	gary at trimm.co.uk; 't10 at symbios.com'
Subject:	Re: Cable swap blows Ultra2 cards?

Gary,

Do your sources report whether the bus was in LVD mode prior to
hot-plugging
the Single Ended drive ?

...Harlan

----------------------------- Reply Seperator
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* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gary Watson <gary at trimm.co.uk>
*

Hi all,
We are hearing an alarming number of reports that attaching a single
ended
disk subsystem to a powered-up PC with an LVD host adapter in it can
result
in catastrophic failure of the host adapter.  Obviously people ought to
switch off everything before changing SCSI cables around, but technicians
tend not to bother as the conventional wisdom is that you don't need to
for
SCSI.  Has anyone else seen this?  Could it be related to the fact that
the
host adapter is operating its multimode drivers in differential mode by
default, and when a live cable is plugged on, DIFFSENS is not the first
wire to mate, and effectively a bunch of active differential drivers get
shorted to ground for a second or two?  I know this theory has a big hole
in it as the host adapter ought to be tristated, but it's all I can think
of unless there is some kind of odd construction being used in the
multimode output pads which blows up if the voltage is out of the
expected
range for LVD operation when trying to run in LVD mode.  I thought about
ground potential between the cabinets, but I've now measured this in two
failed systems and found that the grounds were bonded perfectly.  So I am
at a loss.  Is it possible to deduce the problem by post-mortem
examination
of the silicon?

Gary Watson			Trimm Technologies Ltd.
Engineering Manager		A Subsidiary of Robroy Industries, Inc.
gary at trimm.co.uk		Nottingham NG8 6AR  ENGLAND
http://www.trimm.co.uk		+44 115 951 9951


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