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From: mbarkah@slate.mines.colorado.edu (Ade Barkah)
Subject: Re: 16550 detection
Message-ID: <1994Dec1.144417.129066@slate.mines.colorado.edu>
Date: Thu, 1 Dec 1994 14:44:17 GMT
References: <1994Nov23.111540@estwm0.wm.estec.esa.nl> <3b207m$aps@lorne.stir.ac.uk> <NICKEL.94Nov30212955@toftum.prz.tu-berlin.de>
Organization: Colorado School of Mines
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Juergen Nickelsen (nickel@prz.tu-berlin.de) wrote:
: > Hum, if I beg to differ, baud is afaik an unit of modulation speed, so
: > one can't really use it speaking of a digital link (on which _no_
: > modulation is used.)
: I seem to remember that the baud rate is the number of state
: transitions per second. On a (binary) digital link you have two states
: (high and low or whatever), so you can talk about a baud rate here as
: well.
Ok, let's put this to rest. Juergen is right.
It's important to remember that we're transmitting symbols. Does
this apply to digital transmissions ? Yes. A digital message is
simply an ordered sequence of symbols from a discreet source. This
source has an alphabet 'M' of 2 or more symbols, and produces
the symbols at some rate 'r'.
If we allocate a finite amount time alloted to a symbol, and call
that time 'D', we can for once and ever define what baud is. Having
'D', our "signalling rate" is:
r = 1/D (1)
measured in _symbols_per_second_ or baud. For binary transmissions,
we have a bit duration Tb, and our "bit rate" is:
rb = 1/Tb (2)
measured in _bits_per_second_, (bps, or b/s).
Now we note that in the special binary (M=2) case, each bit is
a symbol and thus D=Tb, and by (1) and (2) we have:
r (baud) = rb (bps) (3)
or in English, for *binary* transmissions, we have "the signalling
rate, measured in baud, is the same as the bit rate, which is
measured in bps." For all other transmissions, the signalling
rate (baud) is not equal to the bit rate (bps).
Regards,
-Ade "never wants to see this again" Barkah