Cable swap blows Ultra2 cards?
gary at trimm.co.uk
Wed Oct 7 00:27:25 PDT 1998
* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gary Watson <gary at trimm.co.uk>
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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