Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!emory!hubcap!dawill
From: dawill@hubcap.clemson.edu (david williams)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Apple SCSI not compatible with standard SCSI?
Message-ID: <7388@hubcap.clemson.edu>
Date: 9 Dec 89 02:39:16 GMT
References: <24105@cup.portal.com> <15450001@hpdml93.HP.COM> <593@bmers58.UUCP>
Organization: Clemson University, Clemson, SC
Lines: 31

In article <593@bmers58.UUCP>, keithh@atreus.uucp (Keith Hanlan) writes:
> In article <15450001@hpdml93.HP.COM>, stephen@hpdml93.HP.COM (Stephen Holmstead) writes:
> > 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.  
> 	
> 	What is meant by "differential SCSI"?
> 	What is meant by "single-ended SCSI"?
> 
> 	Is this something to do with chaining devices?
> 

    Since I seem to have started this, I'll answer your question:  Differential
drive is a technique of sending signals to eliminate noise.  You use two wires
for each signal.  One wire carries the normal signal, and the other wire carries
the signal after being inverted.  At the recieving end, you invert the signal
that was inverted at the transmiter, and add them together.  Any noise on the
line cancels out (since each line gets the same amount of noise placed on it
during the traversal of the cable) and you end up with a clean signal.
   Single-ended means you use just one wire for each signal, and put up with
the resulting noise.  As I understand it, RS-422 is much like RS-232, yet it
uses differential drive.


         ------------------------------------------------------
 /'''''\        Dave Williams
| o   o |          dawill@hubcap.clemson.edu
|   m   |              PeopleLink:  SillyDave
| \___/ |                   Huh?  What?  Could you repeat the question?
 \__U__/     "Ha!  I finally got a reallyyyyy  greattttt  .sig file!"