David van Horn wrote:
>Exceeding 10% error in timng is fatal, but that error includes error in
>timing on the other end.

I am under the strong impression that 3% total is the limit for 8N1.
Because the last known reference is the start of the start bit, and one
needs to read within the center 33% of the stop bit. That's 9.5 bit times
ahead and allowed range is 9.3 to 9.6 So the total timing error should be
0.3/9.3 bit times or better. 0.3/9.5 = 0.03157 ~= 3%. So each end should
be 1.5% or better accurate. Did I oops something here ? Apropos, accuracy
needs to be even better for 8O1. And this brings us to the 'almost right'
baud rate obtained by using the dividers in PICs and other micros with
UARTs...

BTW 508 and 509 code that implements auto speed tuning for RC clocked
operation and RS232 comms requires the same accuracy in the timing tuning
code.  Been there...

Peter

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