> Check the requirements of the RS232.  You might want to consider the
> case where one unit is running at +5% and the other at -5% (if both ends
> are the same unit).  The baud rate accuracy requirement increases with
> baud rate, IIRC.   Also, your PWM frequency will be affected, so, the
> pitch of your sound may vary.  The answer is in the requirements, not
> the opinions of people who don't have the numbers.

I knew this question would bring out all the old misconceptions regarding=20
RS232 baud rate accuracy.

First, the total worst case error budget in RS232 is about 6%. You have to=
=20
remember that both the transmitter and receiver may be off frequency.

Second, required baud rate accuracy is *not* a function of baud rate.=20
Everything just scales so that the same % error is possible at any baudrate=
..=20
(However, a caveat: if the baud rate is so fast that the rise and fall time=
s=20
of the signal make a signficant difference then you might have to adjust th=
e=20
error budget).

IMHO I would *not* attempt to do serial communications without a crystal (o=
r=20
resonator).

-- Bob Ammerman
RAm Systems



--=20
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