On Fri, Jun 21, 2002 at 07:00:58AM -0400, Bob Ammerman wrote:
> > Thanks Bob,
> >
> >         But I forgot to say, that the system will use 2 button cell
> (lithium)
> > batteries in parallel,
> > so Vdd is 6volt, and will use a 4mhz Xtal, cause it has to download data
> > every 1 month.
>
> Is the chip even specced to run at Vdd = 6V ??

Nope. Max is 5.5V. Actually it may be better to parallel the two lithiums and
switch to a LF part that runs reliably down to 2V. The lower voltage and
high available current should combine to extend the available running time.

>
> You could still run with an RC OSC, but then use the 32.768KHz crystal to
> 'calibrate' a timebase for a bit-banged software UART (or, if your baud rate
> is low enough, you could even compute an appropriate value to store in the
> BRGEN and use the hardware UART).

If that's the case wouldn't a syncronous serial interface be better? Then
the internal 37 KHz RC oscillator can be used.

BAJ

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