🚀 go-pugleaf

In <1992Jul27.025718.22038@umbc3.umbc.edu> brian@umbc4.umbc.edu (Brian Cuthie) writes:
| In article <4455@rosie.NeXT.COM> amm@NeXT.COM (Alan M. Marcum) writes:
| >Bob Peirce #305 writes
| >> I have an HSD scanner at the end of my SCSI chain.  Since I don't
| >> use it all the time ... I like to turn it off...
| >> Something I haven't tried is to actually disconnect the scanner
| >> from the CD drive and plug the SCSI terminator in.  That doesn't
| >> seem like a good thing to do on a running system...
| >
| >The SCSI bus is actually an active bus.  To function correctly,
| >all devices on the bus should be powered on, the cables should
| >have the proper impedence, and the bus should be terminated at
| >both ends.  A *very* short bus can be run with termination only
| >at one end (e.g., just the on-board disk, which has a terminator
| >on it).
| 
| This is bunk.  The SCSI bus is driven by open-collector devices.  A 
| properly behaved SCSI peripheral may be left in the powered down state without
| any ill effects.

Ah, thus speaks someone who hasn't dealt with the real world.  Many
(most?) SCSI devices will pull all the bus lines into the active state
when powered off.  In fact SCSI 2 only has an implementors note (NOT a
requirement!) suggesting that powered off SCSI devices tristate the bus
rather than pulling the signals one way or the other.  In my experience
(and I have looked at a *LOT* of different SCSI devices), almost none
do this yet.  Yes, there are some, but not many, for a number of
reasons (cost is one of them).

| Nothing personal, Alan, but is this the kind of answer I can expect from
| NeXT tech support at $225/Question ?

Alan is right, you are wrong.  Of course, if you know it all anyway,
why would would you want to call for support ;)

PS: Hi Alan; ain't supporting customers grand!
--
Let no one tell me that silence gives consent,  |   Dave Olson
because whoever is silent dissents.             |   Silicon Graphics, Inc.
    Maria Isabel Barreno                        |   olson@sgi.com