Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!congrunt!artk
From: artk@congrunt.uunet.uu.net (Art Kreitman @ Congruent)
Newsgroups: comp.sys.ibm.pc.rt
Subject: Re: What is "differential" SCSI?
Message-ID: <4.UUL1.3#5085@congrunt.uunet.uu.net>
Date: 9 Nov 89 21:14:04 GMT
References: <509@ursa-major.SPDCC.COM>
Organization: Congruent Corporation, New York City
Lines: 27

> Path: uunet!snorkelwacker!spdcc!dyer
> From: dyer@spdcc.COM (Steve Dyer)
> Newsgroups: comp.sys.ibm.pc.rt
> Reply-To: dyer@ursa-major.spdcc.COM (Steve Dyer)

> >filled by the IBM streamer seemed like a waste.  I called the local Cipher
> >distributor asking for a SCSI streamer, but unfortunately no one (at that
> >point) had a 1/4" drive with a differential SCSI interface (thanks IBM!),
> 
> Can someone here tell me what "differential SCSI" is, and how it's
> different from the SCSI I'm used to on Macs, {DEC,VAX}station 3100s,
> Adaptec 1542s, and Suns?

   The SCSI spec (ANSI X3.131-1986)  allow for two types of electrical
SCSI bus connections, single ended and differential.
   For single ended, a bus signal is asserted on negated based on the
voltage on a single wire relative to ground. 0 to .4 volts== asserted;
2.5 to 5.25 volts==negated.
   For differential, there is a signal line for assertation and a line for
negation. Assertion is when  "+SIGNAL" is more positive then "-SIGNAL", etc.

   Its all in the spec, if you're claiming to be writing SCSI Device Drivers,
you can't live without it.
Art Kreitman					uunet!congrunt!artk
Congruent Corp. 				congrunt!artk@uunet.uu.net
110 Greene Street
New  York, NY 10012				212-431-5100