Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!van-bc!
From: lphillips@lpami.wimsey.bc.ca (Larry Phillips)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Apple SCSI not compatible with standard SCSI?
Message-ID: <872@lpami.wimsey.bc.ca>
Date: 5 Dec 89 11:28:43 GMT
Lines: 33
Return-Path: <lpami!lphillips>
To: van-bc!rnews

In <593@bmers58.UUCP>, keithh@atreus.uucp (Keith Hanlan) writes:
>	What is meant by "differential SCSI"?
>	What is meant by "single-ended SCSI"?

On any wire that carries an electrical signal, you always need to have another
wire that serves as a reference. If you only have one wire, you can send all
the signals you want down it, and the other end will not be able to tell
anything about the signal.

A differential line is one that has changing signals on both wires. One pushes,
one pulls, as it were. As an example, wire A might go to +5 V, while wire B
goes to -5V. When wire A goes to -5V, wire B would go to +5V.

A single ended scheme has one wire changing states, say from 0 to +5V, while
the other wire sorta says "You push, you pull, I'm gonna just sit here at 0V."

>	Is this something to do with chaining devices?

Not really. It does mean that the circuitry has to be correct for the method on
all devices on the line; you can't mix differential and single-ended methods.
It also works out that differential methods are less noise prone and can
generally drive a longer cable.

-larry

--
" All I ask of my body is that it carry around my head."
         - Thomas Alva Edison -
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|   //   Larry Phillips                                                 |
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