> A sneaky trick is to use 'tuning' to get your timing right. Instead of ju=
st loaded
> a value into the baud rate divisor and forgetting it, you sample incoming=
 data
> bits to determine their length, and then use the results to set the baud =
rate
> divisor appropriately. This is very useful in a poll and respond scenario=
..
>=20
> On one project I used it by polling the incoming data line, looking for a
> transition to high (the start bit). By having the host start each message=
 with a
> byte of 0x0F you will see a 5 bit high time (the start bit and 4 one-bits=
 of data)
> followed by a 5 bit low time (the high order zero bits of the data follow=
ed by
> a zero for the stop bit). I just time the 5 bit high time and compute the
> apparent baud rate from that (which will of course be different from the =
real
> baud rate depending on the accuracy of the PICs clock). Then I program th=
e
> baud rate generator and enable the receiver. The receiver will start scan=
ning
> for the next start bit sometime in the middle of the 5 zero bits, so it w=
ill pick
> up the first data byte following the 0x0F trigger.

This is very similar to the LIN protocol, which is used in the PIC chips th=
at will autobaud. Microchip have a couple of application notes on it.


--=20
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