David VanHorn <dvanhorn@CEDAR.NET> wrote:
>Hmm.. I'd really not want to do it without an int.
>You could be anywhere in the bit, and not know it.

With regular sampling at N x baud rate, you can look out for a high-to-
low change, then delay for (N / 2) sample periods to get roughly in the
middle of the start bit.

This isn't as precise as interrupting on the start bit edge, but will
work okay with suitably high values of N.  I've used N = 8 before, and
Alan Pearce has good reason to believe that N = 4 is okay in many cases
(see his earlier posting).

However, I'd be nervous about the timing uncertainty for smaller values
of N if there is a possible difference of more than a couple of percent
in the baud rate clock frequencies at each end.  This shouldn't occur if
both ends run from crystals which divide down exactly, but I know from
experience that some designs take liberties with this (inexact divisors
leading to frequency offset, RC oscillators with poor accuracy etc.).

All the best.
--
Ian Chapman
Chapmip Technology, UK

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