>> It is.  The zip drive actually has two DB25s on it, one "in" and one
>> "out".

> Right.  Some of LaCie's drives came like this, too.

>>> and you'll find an appropriate adapter cable at any Macintosh shop
>> Hardly.  The drive comes with a cable designed to connect it to a
>> Macintosh; it's male DB25 on each end, but is _not_ symmetric: flip
>> the cable end-to-end and it won't work.
...or at least so I'm told by someone who tried it by accident; it may
be, as you say, that that particular cable was defective.  I haven't
taken an ohmmeter to mine.  Yet. :-)

You also write in reply to this, in another message,

> HMMMMMMM.  Does the Iomega drive have switchable termination?

Yes.

> Does it have an external terminator widget that you plug into the
> unused port?

Mine didn't come with one.

> If the answer to both questions is "no", that *could* be the reason
> the cable isn't symmetric -- one end might contain terminators.

Apparently not; the docs mention chaining other devices off the "out"
connector, with the terminator switch set to off.

> I just checked Iomega's web page (http://www.iomega.com/, natch).
> They are astonishingly nonspecific about cabling requirements.  And
> they don't supply a customer support address, either.  Thanks, guys.

The paper docs that come with the drive say info@iomega.com.  But I
wrote to them months ago, back when I first got the drive, asking four
specific questions...and to date I haven't gotten any response.  I
think on Monday I'll phone their 800 number and camp in the queue until
I get to a human and ask my five questions.  (Yes, one more question
has come to mind since I sent the first email.)

>>> ([...] a fairly rare DB25-to-DB25 *SCSI* cable; note that a 25-wire
>>> serial cable *won't* do).
>> Why not?
> A SCSI cable needs 50 wires, in 25 pairs (well, 23 pairs I think),
> because each signal line MUST be a 100-ohm TRANSMISSION LINE, not
> just a wire.

Ah.  Heh.  So a 25-pin scsi cable is 25 twisted pairs, with the ground
wires all tied together at the two ends....

>> Except what I need is a cable to connect it to a (so-called) DB-50.
>> Not a Centronics-50.
> A DB-50?  You mean something that looks like a stretch DB-25, with
> pins and everything?

Well, I'm told the proper name for it is a DC-50, because it's got
three rows of pins, but everybody calls it a DB-50.

> What the hell uses that?  (Or is this a Sun, with that tiny mutant
> three-row connector?)

It ain't tiny; the pin spacing is the same as for a DB-25.  What uses
it?  Just about everything, or so I thought until I tried to find a
Macintosh-to-"DB50" scsi cable.  It certainly is available as one of
the standard connector options when ordering a drive from the local
retail disk resellers....

>> We've found a shop that is willing to do custom cables, and are
>> having them wire up an appropriate cable, based on handing them the
>> above mess and saying "here's your reference for the wiring".
> Make sure they understand how to wire *SCSI* cables, as transmission
> lines, or you will likely come to grief.

Thanks for the warning.

					der Mouse

			    mouse@collatz.mcrcim.mcgill.edu