Bill,


Using BRG16 =3D 1 and BRGH=3D 1 changes the formula to Fosc / ( 4 * rate ) =
-
1, resulting in many more options of dividers.
With FOsc =3D 48MHz and the above setting you can obtain all the normal
baud rates from 300bps and up with an error of at most 0.2%.


Isaac



Em 23/3/2012 09:30, Bill Stoddart escreveu:
> Thanks to everyone who chimed in, it got me thinking through the problem
> better.
>
> I think I am doing the calculations correctly but some of the baud rates
> I'd chosen must have had too much of an error.
>
> I am able to run at 9600 with 8 bit, BRGH=3D0, BRG=3D78 and at 115200 wit=
h 8bit
> BRGH=3D1, BRG=3D25.
>
> I tried to run 9600 with 8bit BRGH=3D1, BRG=3D311 with no luck.
>
> This is all still using 48MHz.
>
> Thanks again
> Bill
>
> On Fri, Mar 23, 2012 at 7:26 AM, <alan.b.pearce@stfc.ac.uk> wrote:
>
>>> A 'hexadecimal' crystal is more suitable for common baud rates, but
>>> whether you can or do use one depends on the functional priorities. For
>>> example if a microsecond timer is more important than comms, then a
>>> 20MHz would be preferable (for the 200ns cycles). You might have to
>>> compromise somewhere
>>>
>>> An 18.432MHz crystal in the calculations
>>>
>>> ((18432000/115200)/16)-1
>>>
>>> =3D 9.000000, no error
>>>
>> There is also a 19.something that gives exact baud rates (19.66088? or
>> something like that). The other option would be to 'overclock' slightly =
at
>> twice 12.288 which is also an exact baud rate frequency (hence it tended=
 to
>> be used as the standard frequency for 8080 CPUs).
>>
>>
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