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From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.lan
Subject: Re: Ethernet Transceiver Cable question...
Message-ID: <89@redwood.UUCP>
Date: Sat, 1-Dec-84 10:28:55 EST
Article-I.D.: redwood.89
Posted: Sat Dec  1 10:28:55 1984
Date-Received: Tue, 4-Dec-84 05:25:41 EST
References: <326@rna.UUCP>
Organization: [Consultant], Foster City, CA
Lines: 25

There is no official minimum transceiver cable length. However, what
you are seeing may be some interaction between the Interlan controllers
and the DELNI. In particular, if one side is configured for Ethernet
Version 1.0 and the other for 2.0, there is a spec on the "idle state"
of a transceiver signal pair that may be causing trouble. The 1.0 units
expect the other side to maintain a solid differential "1" when idle;
2.0 (and IEEE 802.3) specifies a "decay to idle" which is more-or-less
an ECL "tri-state" (no differential voltage).

Now if the "squelch" on the 1.0 side is set too low (or is missing),
such a "tri-state" condition is a candidate for picking up noise,
causing your erratic performance. Adding 50 feet of cable may put
enough capacitive load on the lines that the noise problem goes away.

Alternatively, there is a spec on the decay-to-idle time, which one
side or the other may be violating in the absence of enough capacitive
load.


Rob Warnock

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