[3404] in linux-scsi channel archive
Re: CD-ROM resets SCSI bus on Buslogic BT-958
daemon@ATHENA.MIT.EDU (Michael Weller)
Wed Feb 25 07:21:55 1998
Date: Wed, 25 Feb 1998 11:07:05 +0100 (MEZ)
From: Michael Weller <eowmob@exp-math.uni-essen.de>
To: Jeff Collins <collinsj@ece.ucdavis.edu>
Cc: Brendan Miller <brmiller@wco.com>, linux-scsi@vger.rutgers.edu
In-Reply-To: <Pine.HPP.3.95.980224130146.7037D-100000@orwell.ece.ucdavis.edu>
On Tue, 24 Feb 1998, Jeff Collins wrote:
> On Mon, 23 Feb 1998, Brendan Miller wrote:
>
> > > I was having somewhat similar problems when I attempted to add a CDROM
> > > burner and a SCSI tape drive to my system (a Buslogic 946 w/ 2 SCSI
> > > disks). My problem turned out to be that I had been using passive
> > > termination on one end of the bus. With only the 3 existing devices, I
> > > didn't notice any problems. However, on trying to extend the bus, things
> > > must have gotten out of spec and I started getting command timeouts and
> > > the like. So, is your narrow bus passively (with resistors) or actively
> > > (by jumpering to "enable termination") terminated? --jw
> >
> > I don't know--the ZIP drive has "Termination-On". It's a slide-switch.
> > I don't know what kind of termination it provides. The other end of the
> > narrow bus is the Buslogic card--supposedly, it "auto-terminates as
> > necessary".
>
> That's active termination. Termination that's enabled with software,
> jumpers, or switches is active. If it were passive, you'd have 2-3 inline
====== Nope!
> resistor packs that you'd have to mess with. You don't have the problem I
> described. I don't have any other brainy ideas. Good luck. --jw
While you describe passive termination correctly, active termination does
not use (passive) resistors but active OpAmps (Operation Amplifiers using
transistors and such) to 'actively' pull the (floating) bus lines to a
defined level. If termination is enabled by a jumper/software or not is
not directly related to active or passive termination at all. External
terminator plugs using active termination are available since ages (though
the resistor pack type is cheaper) (usually they are those with control
LEDs for working termination power)
One might argue though that those devices using a jumper or software
setup to enable termination are so decent that they'll use active
termination anyway, but I don't know if this holds in reality.
Note that ULTRA SCSI (20MHz) (to an extent even Fast (10MHz)) REQUIRES
active termination, at least as far as I know. And this holds even if
there is only a single device on the bus which can in theory support that,
because it's input lines will be very sensible then, even when the fast
speed is never actually used.
Michael
--
(^ )
(+--- For the browser damaged young people: THIS IS A SIG!)
(Michael Weller: eowmob@exp-math.uni-essen.de, eowmob@ms.exp-math.uni-essen.de,
or even mat42b@spi.power.uni-essen.de. If you encounter an eowmob account on
any machine in the net, it's very likely it's me)
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.rutgers.edu
