Re: Some upgrading questions...

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <3i0bcf$6o9s@blue.weeg.uiowa.edu>,
Steven Nelson <snelson@blue.weeg.uiowa.edu> wrote:
> From article <D432z9.98L@actrix.gen.nz>, by
> dempson@atlantis.actrix.gen.nz (David Empson): 
> > There are two versions of the Apple SCSI card.  The original one has
> > three ROM releases, of which only the latest (revision C) should be
> > used.  The High-Speed SCSI card was modified to add termination power,
> > but has never had (or needed) a ROM upgrade.
>
>  I do believe David made a typo above.  The HS SCSI provides termination
>  but the older SCSI card didn't.

No typo - I didn't even mention whether termination was provided by
either card.  I was only talking about termination power, which is
only supplied by modified HS SCSI cards.  Neither card was designed to
supply termination power.  The modification consists of a diode (and
preferably a fuse, but I don't think the suggested modification
mentions that).

I don't think this modification is a particularly good idea.
Supplying termination power requires up to 480 mA from the 5V line.
There is a total of 500 mA available to all cards in all slots, so you
might be overloading the power supply.

(Actually, my main point was to refute the previous poster's claim of
thousands of ROM revisions, which only applies to the RAMFast.) :-)

> David may be right, however, as some have claimed Apple did have a
> revision that did provide term power. 

That's what I was talking about.  I haven't seen any of these cards, though.

> So my HS SCSI cards may or may not provide term power.  I don't know
> how to tell.

Look for the added diode, I suppose.

> They both provide termination however.

Yep.  (Both "versions" of the HS SCSI card, that is.  The original
Apple SCSI card is not terminated.)

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand