On Thu, 22 Jun 2000, Byron A Jeff wrote:

> One last thing:
>
> The bit generation need not be exact because each character is self clocked
> independantly of the others. While it seems from my previous example that a
> start bit start on a bit boundary, it can in fact start at any time.
> Typically serial ports will operate correct up to 4 percent error or so.
> For 9600 BPS that means that any clock from 9216 BPS to 9984 BPS (100 to
> 108 uS bit cell time) the character will be interpreted at the other end
> correctly. This is why it's possible to generate 9600 BPS characters at
> 4 Mhz or 10 Mhz when 9600 isn't an exact multiple.

But a phase accumulator or careful isochronous coding makes this a moot point.

Also, a good tutorial on a software UART can be found on Eric's page:

http://www.brouhaha.com/~eric/pic/bitbanging.html

Scott