>>>>> "John" == "John F Woods" <jfw@jfwhome.funhouse.com> writes:

John> A SCSI cable needs 50 wires, in 25 pairs (well, 23 pairs I
John> think), because each signal line MUST be a 100-ohm TRANSMISSION
John> LINE, not just a wire.  If you put SCSI signals on something
John> other than a 100-ohm transmission line, you WILL get reflections
John> which can distort the signals and corrupt data, just like when
John> you don't use terminators.  The 25 pin connector introduces a
John> small impedance bump, but fortunately not a fatal one (the
John> severity of reflections is a product of both the impedance
John> difference and the length of the impedance mismatch).

	I find this somewhat interesting.  Several Amiga drive
manufacturers also have put out controllers with 25 pin DB
connecters.  From reading the pinout from some HD that I used as a
reference (to wire my own DB 25 to 50 pin header cable), around about
1/2 of the SCSI wires run to ground in a cable.  I always beleived
that this was just for reducing the impact of cross wire interference.

	Anyways, after building my own 25 to 50 cable (tying every
other wire (almost) to ground... it worked for years.  Until I found a
working one at a surplus store for $5.

>> Except what I need is a cable to connect it to a (so-called) DB-50.
>> Not a Centronics-50.

John> A DB-50?  You mean something that looks like a stretch DB-25,
John> with pins and everything?  What the hell uses that?  (Or is this
John> a Sun, with that tiny mutant three-row connector?)

	He is probably talking about a Sun cable.  I have called them
DB-50 too, but they're not quite.  They're a little longer than
db-25's, and wider due to the three rows of pins.

Dave.

-- 
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|David Gilbert, PCI, Richmond Hill, Ontario.  | Two things can only be     |
|Mail:      dgilbert@jaywon.pci.on.ca         |  equal if and only if they |
|http://www.pci.on.ca/~dgilbert               |   are precisely opposite.  |
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