Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!ucsd!ucbvax!hplabs!hp-ses!hpdml93!stephen
From: stephen@hpdml93.HP.COM (Stephen Holmstead)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Apple SCSI not compatible with standard SCSI?
Message-ID: <15450001@hpdml93.HP.COM>
Date: 22 Nov 89 16:12:57 GMT
References: <24105@cup.portal.com>
Organization: Hewlett Packard - Boise, ID
Lines: 27

David A. Kavanagh (dak%ritcv@cs.rit.edu) writes:
>  Look in Amazing computing from quite a few months ago.  Then show the
>pin-outs for the 25pin and 50 pin SCSI connectors.  It seems that half
>of the 50 pin cable is for grounds.  That's how Apple got it down to 25
>pins.  They use the sheild as a return ground for the signals.  I think
>that some of the other pins might be ground to, (I haven't looked at
>the pin-outs in some time).

Just a warning to people who want to get rid of 50 pin SCSI connectors
(eg. Apple Computer):  Half of the pins on a 50 pin connector are
grounds ONLY on a single-ended SCSI device.  On differential SCSI
devices, all 50 pins are used.  When Apple went to a 25 pin SCSI port,
they made a statement that do not want to consider anything but a
single-ended SCSI device.  In the *REAL* world, people use 50 pins for
both single-ended and differential drives, thus creating a 'standard'
(heaven forbit if Apple ever used a 'standard' cable!). :-)

Just thought everybody in net-land would like to know before we started
getting the "why do we have 50 pin SCSI connectors anyway?" articles.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Stephen Holmstead
...!hplabs!hpdmlge!stephen                      //
Hewlett Packard Disk Memory Division          \X/  Amiga Forever!

"I remind you that humans are only a tiny minority in this galaxy."
	-- Spock, "The Apple," stardate 3715.6.