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Thread: What is baud rate
www.piclist.com/techref/index.htm?key=what+baud+rate
BY : Philippe TECHER email (remove spam text)

Hi,

Someone compare Baud rate and old method of semaphore ...
I don't follow exactly the whole discussion about baud rate, but I can
explain exactly what is it:

Suppose you have a D/A converter with 2 bits input. Then, you have 4 state
level at the ouput, for example:
00  -> 0V
01  -> 1V
10  -> 2V
11  -> 4V

If you connect the output of the converter to a transmission line you can
transfert the signal between 2 device A and B. If you change the code of the
A/D converter 2 time each second, you transfert two voltages levels per
second. This is the baud rate, exactely, it's the number of the different
state level per second.
In this example we have:
Baud rate = 2 Bd/s
Number of state level = 4
bit-per-second = 4 bit/s

We can simply determine the Bit-per-second rate as follow:

Bit per second = baud rate * [ln (Number of state level)] / [ln 2]

If we have only 2 states level (0 or 1 for example), baud rate equal bit rate.
The best example of this difference between bit/S and Bd/s is in a modem.
The Bit/s rate between computer and modem is the same that Bit/s rate
between modem and phone line. But the baud rate is not the same, Modem use
(for example) 8 phase shift modulation to transmit the signal, in this case
Modem baud rate equal 1/3 of computer baud rate.

I hope to be clear enought ...

Regards.
Philippe.
<9512130733.AA09307@MIT.EDU>

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