Date   : Wed, 25 Mar 2009 12:41:42 +0000
From   : pete@... (Pete Turnbull)
Subject: Fwd: BBC B to PC serial cable

On 25/03/2009 11:10, Rob wrote:
> 2009/3/25 Pete Turnbull <pete@...>:
>> I think you're mixing up RS232 and RS423.  Max length often quoted for
>> RS232 is 50 feet or 15m but the old standard actually said 45 feet as
>> guaranteed distance and that the real limitation was on cable
>> capacitance: you should expect to go much further with decent cable
>> rather than lighting flex.
> 
> Much much further...  Obviously not Beeb based, but we used to use
> RS232 for terminals and would typically run them the entire length of
> a building, several hundred meters, with the ups and downs..  Only in
> exceptional circumstances did we need to drop any lower than 38,400
> baud - lots ran at 115,200..

Yup, we did things like that too, even between buildings.  Not quite as 
fast, but only because the terminals didn't support baud rates that 
high.  All the RS232 standard says, in effect, is that if you don't 
specify sensible cable, the most the designers would guarantee in a 
worst case environment was a short distance.  But RS232 was designed to 
be robust in noisy environments with all sorts of telephone wire, 
parallel-core lighting flex, and other crap (technical term) and they'd 
guarantee that 45' with all sorts.  Some manufacturers of driver chips 
even provided tables or charts showing how you should really be able to 
go at different speeds by taking account of the capacitances and 
loadings, and 45 feet was often off the bottom of the chart.

-- 

Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York