Posted on March 24, 2003 at 17:15 Hello Dimos,
Basically there is only two choices.
If you look at the baud rate formulas (chapter 4 of the user's manual) you have only two choises according to the bit (SOBRS):
Code:
(SOBRL) = (Fcpu / {16 x [ 2 + (SOBRS)] x Basync})- 1
with Fcpu=20MHz and Basync=57600bauds we have
either (SOBRL) = 9.85 rounded to 10 AND (SOBRS) = 0
or (SOBRL) = 6.23 rounded to 6 AND (SOBRS) = 0
If we use the rounded value in the backward formula (same page)
Code:
Basync = Fcpu / { 16 x [ 2 + (SOBRS)] x [ (SOBRL) + 1]}
we get:
for ( S0BRS=0; S0BRL=10) we have Basync = 56818Bauds ( ~57600 - 1.376% deviation) and
for ( S0BRS=1; S0BRL=6) we have Basync = 59524Bauds (~57600 + 3.232% deviation)
Those values are close enough to establish a communication with most of the UART compatible cell available on the market.
If your application require a very precise baud rate, you may have to use a specific crystal (baud rate crystals).
Using the same method, we can calculate the closer speed to 230400 bauds.
The closest we can go with a 20MHz clock is 208333
( - 9.6% frequency deviation) with either ( SOBRL=2; S0BRS=0) or ( S0BRL=1; S0BRS=1)
The higher the baud rate, the bigger the deviation can be...
The maximum speed of the cell at 20MHz is 625kBauds with ( SOBRS=0 ; S0BRL=0).
[ This message was edited by: Max on 24-03-2003 21:50 ]
[ This message was edited by: Max on 24-03-2003 21:54 ]
[ This message was edited by: Max on 24-03-2003 21:57 ]
[ This message was edited by: Max on 24-03-2003 21:59 ]
