On Thu, 17 Jan 2002, Byron A Jeff wrote:

> > Don't trust the tables.
>
> I never have. For all things relating to the PIC USART I use Fr. Thomas
> McGahee's highly annotated code the describes the operation of the USART,
> including the formula for bit rate generation. It's an invaluable resource
> for dealing with the USART and includes many 'gotchas' that have been learned
> from hard experience. Check it out here:
>
> http://mcgahee.freeservers.com
>
  Agree. However I don't found any diferences between standard formulas:

spbrg = (xtal[hz]/(baudrate[bps]*64))-1 for brgh=low
spbrg = (xtal[hz]/(baudrate[bps]*16))-1 for brgh=high

  and rounded formulas:

spbrg_value = (((d'10'*XTAL_FREQ/(d'16'*baudrate))+d'5')/d'10')-1
spbrg_value = (((d'10'*XTAL_FREQ/(d'64'*baudrate))+d'5')/d'10')-1

  the result is +/- 1 diference in spbrg value which means almost nothing,
my test shows that at many baud rates even with +/- 3 from computed spbrg
values does not affect asynchronous communications ( not applicable with
small spbrgh ) Of course the computed error must be smallest as possible.
So my question: do you found any situation when rounded formulas
must be applied ?

regards, Vasile

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