piclist 2001\02\13\212739a >
Thread: RS232 baud rates
face BY : Dan Michaels email (remove spam text)

Drew Vassallo wrote:
>Interestingly, I've found a number of serial routines that use 9600 baud
>(nice 104.167us per bit) and 19200 (nice 52.08us per bit), but none for
>38400 (even nicer 26.04us per bit).  I wonder why nobody uses this.
>I changed my half-bit delay routines for my 19200 baud to 38400, and guess
>what?  It works better than my 19200 baud transfer, as expected.
>Anyone care to elaborate on the mystical 19200 barrier?  Of course, it's
>really only practical for cases where you are sending/receiving
>synchronously with the rest of your code.  Asynchronous at high speeds is,
>for all practical reasons, impossible.

38400 is basically the only thing I use anymore. But then, I
pretty much always use 20mhz xtals.

People who use 4/8 mhz xtals are probably used to using 9600/19200
- that's my guess. Also, when using the PIC UART with lower freq
xtals, choosing 38400 may translate into SPBRG values that produce
large baudrate errors. Third guess is inertia.

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See also: www.piclist.com/techref/microchip/ios.htm?key=rs232
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