AVR-Chat

The ADC clock needs to be in a fairly narrow range if the
accuracy specs are to be met. If its too slow, the
sample-hold cap will loose some of its charge and the
converter won't work right. If its too fast, you will loose
accuracy.

But, since the processor clock can vary over a rather wide
range, the ADC prescaler lets you select an ADC clock thats
in the specified window. 

If you have a slow processor clock, then, YES you want (and
need) to use the minimum prescale value. But, if the
processor clock is faster, then you need to adjust the
prescale value accordingly.

Jim
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