AVR-Chat

Hi guys,

Only bit of advice that I can give from my own experience is that the
on chip RC oscillator is FINE for UART when your running on a accurate
5V supply AND you program the OSCCAL register with the correct value.

If your VCC is low (3V or 3.3V) etc, you can still use the UART by
setting the value of OSCCAL correctly (Not the value that the
programmer gives you), I have done this by entering into a loop where
I increment the OSCCAL register, then output it's value out the serial
port, as soon as you can read the value, you know you have a value for
OSCCAL that will allow the UART to work correctly. This is NOT a good
way to do things for mass production, but is fine for homers and
on-offs. The loop looks something like:

OSCCAL = 0;
while(OSCCAL < 255){

  OSCCAL++;
  UART_Write_Number(OSCCAL);
}


Cheers
Hein B
Auckland, New Zealand

--- In AVR-Chat@yahoogroups.com, dlc@... wrote:
>
> > On 5/30/07, dlc <dlc@...> wrote:
> >> I've gotten 9600 baud to work well with the internal 1MHz
oscillators of
> >> the Tiny11.  You can handle quite a bit of slop reading serial
data if
> >> your baud rate is low enough.
> >
> > Unfortunately, clock speed error is proportional, so 5% error is 5%
> > error in baud rate, no matter what baud rate you pick.  But, as the
> > baud rates get higher, the granularity of the steps in the UBRR
> > setting get proportionally larger (ie: 20 vs 21 is smaller error than
> > 3 vs 2)
> 
>   There is no hardware UART in these small chips, I bit bang my serial
> there and that seems to be more tolerant of bit slip and stretch.  Being
> in software gives me the option of very high granularity.  The hardware
> UARTS are not as tolerant of error.  That is probably the difference.
> 
> DLC
> --
> Dennis Clark
>