Apple SCSI TermPWR; Was Re: This is funny (ebay)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Sun Feb 24 16:40:18 2002

See below, plz.

Dick

----- Original Message -----
From: "Doc" <doc_at_mdrconsult.com>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, February 24, 2002 8:09 AM
Subject: Re: Apple SCSI TermPWR; Was Re: This is funny (ebay)


> On Sun, 24 Feb 2002, Richard Erlacher wrote:
>
> > Is it possible you're mixing two things up? Most of the later SCSI drives
<snip>
> > handled by a separate option.
>
> If I understand correctly, you're asking if I know (and implemented)
> the diffference between Term Power and Termination. Yes. Typically, I
> supply termPWR from the terminating device, if possible. Easier for a
> feeble mind to track.
>
Yes, it's easier to track where the termination is if you can see the
terminator. If Termpwr is present, even from one device, easily visible if
you use one of the "active" terminators that has an indicator LED, and the
terminations are present at both ends of the cable, things should work OK.

The device ID can make othewise healthy devices invisible as well. If two
devices use the same device ID, most often neither of them will be visible,
and certainly, neither will function properly. What I do on my PC's, is keep
the internal device ID's lower than 4 and the external ones above. I use 7
(the controller's ID) as the dividing line with WIDE SCSI. The server, for
OTOH, has drives on ID=15 through ID=8 internally, and the external devices
use addresses in the range 1..6, with no ID of 0, though that option is still
open, for either internal or external devices.
>
> > Since the Apple SCSI doesn't provide Termpwr, and since Termpwr is
supposed
<snip>
> > device if it isn't provided otherwise.
>
> Right. If you look at the list of computers I've had trouble with,
> they're all Apples with a single internal device. I don't know if it
> makes any difference, but all the Hawk drives I've got came from Sun.
> All have internal terminators, not R-packs. I have three or four
> around. The one that's in the IIci is an ST31200N. It works just fine
> if I power termination from the drive and use a terminated cable. The
> Mac can't see it at all if I power termination from the drive and enable
> the drive's terminators.
>
Do you mean that the drives have jumper programmable terminators?
>
> > In general, it's easy simply to stick an external terminator on the ends
of
<snip>
> > installation/moving/easter-egg-hunt-for the external terminator.
>
> I'm quite familiar with the easter-egg-hunt.... Whenever I spend more
> than 5 minutes looking for a terminator, external or internal, I buy one
> next time I see one. At GoodWill, if possible. That means I have a
> bunch of spares, stashed in suitably surprising locations.

> I also have to admit I'm real lazy about this. If I use cable
> termination. I don't have to remember the jumper layout of all the SCSI
> drive models I have. I just use a terminated cable if possible and plug
> stuff in.
>
I like to download a copy of the jumper sheet and other requirements for my
externally packaged devices and put that sheet in the enclosure with the
device in question if at all possible. The externally packaged units get much
less internal attention than the internal ones, so it's likely I'll have less
trouble finding the info if it's in the box.
>
> Doc
>
That's abolutely the easiest way to do it. I can't magine why this doesn't
work with the Apple products, though.
>
Received on Sun Feb 24 2002 - 16:40:18 GMT