10 Jul
2009
10 Jul
'09
4:27 a.m.
Teo Zenios wrote:
----- Original Message ----- From: <trag at io.com>
To: <undisclosed-recipients:>
Sent: Thursday, July 09, 2009 4:05 PM
Subject: Re: Classic mac fun (and some questions)
(continued...again...)
From: "Jeff Walther" <trag at io.com
To: cctech at classiccmp.org
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> Date: Thu, 9 Jul 2009 12:00:48 -0400
> From: Ethan Dicks <ethan.dicks at gmail.com
Neither of my IIfx systems need that terminator to work.
I wonder if using an active terminator would work as a substitute for the
special Apple terminator ?
Anyone know a way to check a terminator to see if it is the special one ? I
have one black one that was given to me as a believed IIfx terminator,
but it is
not an Apple one.... so I don't want to trust what it is merely because
it is black.
Anyone know how to ID which IIfx systems need the black one, and which
ones are
of later rev that don't need it ?
-- Curt
I tried to look that up and found it easy to see
that the IIfx needed
something odd (I couldn't find specifics), so well done there. It
would be interesting to get the details to see where Apple went off
the rails from the SCSI spec.
IIRC, it's a matter of adding a capacitor and maybe a resistor to a
regular terminator. There's an Apple Technical Note or similar
available
somewhere. I probably have a copy squirreled away on my hard drive at
home. And I think I remember that they use a somewhat higher value
capacitor (so add a smaller one in parallel on an existing
terminator) and
a lower resistance (so again, add a resistor in parallel). But I could
be misremembering.
Again, IIRC, the IIfx's SCSI was too noise sensitive. But I've also
heard/read that that was only true for the early production run and that
the later built machines did not need the funny terminator.