Sorry, yes, you do draw more current when idling with a fixed oscillator 
on the input than you would when idling running off the internal RC.  
And it is significant if you're going to be powered up all the time.  I 
think the best bet is to run with the PLL and jack up the speed when you 
need it (as Adam suggested).

Thanks,

Tony




solarwind wrote:
> On Tue, Jan 27, 2009 at 4:43 PM, Tony Vandiver
> <tony@traceelectronics.com> wrote:
>   
>> It's not the external oscillator that consumes more power, the micro
>> consumes more power the faster it runs.
>>     
>
> That's what I mean. In my design, the micro will run at full speed
> when performing a calculation and immediately go to sleep. It will be
> woken  by an interrupt-on-pin-change, then scan the keypad and perform
> a calculation or operation and immediately go to sleep. If I use an
> external clock source, will the clock still be pulsing even after the
> micro is asleep? And that's what I'm worried will waste a lot of
> energy.
>
>   
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