SiLabs C8051F34x and baud rate generation from internal oscillator

I know that this IC is able to be used with its internal oscillator
when it is used for a USB clock with clock recovery to make it work,
however can the internal oscillator be used for clocking the UARTS, I
need one of the 2 of them to run as fast as it can! which I read is /
16 or 3Mhz... on receive.

Anyone know the answer... very hard to dig this one up.

Richard.

themindfactory@gmail.com wrote:
> 
> I know that this IC is able to be used with its internal oscillator
> when it is used for a USB clock with clock recovery to make it work,
> however can the internal oscillator be used for clocking the UARTS,
> I need one of the 2 of them to run as fast as it can! which I read
> is / 16 or 3Mhz... on receive.
> 
> Anyone know the answer... very hard to dig this one up.

UART clocks need to be highly accurate.  Internal clocks are
generally based on RC oscillators, and nowhere near sufficiently
accurate.  You need a crystal.

-- 
 Chuck F (cbfalconer at maineline dot net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net>



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themindfactory@gmail.com wrote:
> I know that this IC is able to be used with its internal oscillator
> when it is used for a USB clock with clock recovery to make it work,
> however can the internal oscillator be used for clocking the UARTS, I
> need one of the 2 of them to run as fast as it can! which I read is /
> 16 or 3Mhz... on receive.
> 
> Anyone know the answer... very hard to dig this one up.

The SiLabs USB devices spec +/- 1.5% on the Osc.

Most other devices are 2%, but their newest C8051F530's claim 0.5%

How accurate is the 'other end' - is the error budget the same at each 
end, or is one end Xtal derived ?

Another approach would be a calibrate phase, and then you only need to
manage drift. The Calibrate scheme would allow the highest baud speeds,
as you do not have large divide for trim, but must get the Osc freq
in the centre of the error budget.

-jg

Jim Granville wrote:
> themindfactory@gmail.com wrote:
> 
>>       I know that this IC is able to be used with its internal
>> oscillator when it is used for a USB clock with clock recovery
>> to make it work, however can the internal oscillator be used
>> for clocking the UARTS, I need one of the 2 of them to run as
>> fast as it can! which I read is / 16 or 3Mhz... on receive.
>>
>> Anyone know the answer... very hard to dig this one up.
> 
> The SiLabs USB devices spec +/- 1.5% on the Osc.
> 
> Most other devices are 2%, but their newest C8051F530's claim 0.5%
> 
> How accurate is the 'other end' - is the error budget the same at
> each end, or is one end Xtal derived ?

Even accepting your 1.5% figures, all margin has been eaten up on a
normal installation.  And that does not account for initial
misadjustment, or drift, etc.  Relying on it seems, to me, to be
very foolish.

-- 
 Chuck F (cbfalconer at maineline dot net)
   Available for consulting/temporary embedded and systems.
   <http://cbfalconer.home.att.net>



-- 
Posted via a free Usenet account from http://www.teranews.com