*BSD News Article 37625


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From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: 16550 detection
Message-ID: <Cyws7o.JvG@zoo.toronto.edu>
Date: Mon, 7 Nov 1994 17:50:11 GMT
References: <TYTSO.94Nov1182557@dcl.mit.edu>> <MICHAELV.94Nov1215132@MindBender.HeadCandy.com> <Cynu1H.Is@pe1chl.ampr.org>
Organization: U of Toronto Zoology
Lines: 14

In article <Cynu1H.Is@pe1chl.ampr.org> pe1chl@rabo.nl writes:
>I have extreme doubts about using an RS-232 interface at 230400 bps...
>Even 115200 is already way above spec, and can be unreliable with
>standard cables.

Sorry, 115200 is well within spec.  The limits on RS232 are set by the
requirements that slew rate not exceed 30V/us and that transition times
within the forbidden range (-3V to +3V) not exceed 0.04 bit times.  At
maximum slew rate, you cross the forbidden range in 200ns.  If that is
0.04 bit times, the bit time is 5us, giving a maximum rate of 200kbps.
230400bps is outside the spec, but 115200 is not.
-- 
Justice for groups that doesn't include justice    |       Henry Spencer
for individuals is a mockery.                      |   henry@zoo.toronto.edu