Scott WALSH wrote:
>
> Dear All,
>
> I am having difficulty in deciding what speed resonator/crystal to run a micro
> off and it is coming down to what the tolerances are for communicating with th
e
> UART in a PC at the standard 9600bps.
>
> I have looked up the datasheets for the National 16C550 UART but there is a la
ck
> of timing diagrams to show me what I need to know.
>
> The closest I can get my micro to 9600bps, is 9420bps, and I have no idea
> whether this has a chance of working after taking into account the tolerance o
f
> the resonator has on the bps rating.
>
> regards,
> SW.

Not answer all your questions, but take a look at:
http://www.ustr.net/8051pc/starting.htm
at the bottom, read "CLOCK SIGNAL", hope can help you a little bit to
understand the allowed clock slack at asynchronous communication.

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm