AVR-Chat

--- In AVR-Chat@yahoogroups.com, Craig Limber <ffdude@s...> wrote:

> ... how much accuracy do I lose? 
> ... with an 8 MHz clock and a
> prescale of 2?  I ... am only
> interested in 8 bit readings but
> want a high sample rate.  

I don't have the ATmega128 data sheet with me, but this is fairly 
well spelled out in the ATmega64 data sheet. The Absolute Accuracy 
falls from 1.5 LSB at 200 kHz ADC clock to 3 LSB at 1 MHz (the 
maximum), both figures being typical with no worst case given.

The smallest prescaler you can use with an 8 MHz clock is 8. All bets 
are off if you try to go faster.

What do you mean by "8 bit readings"? Resolution? Absolute accuracy? 
Monotonicity? At 1 MHz clock (77 kHz sample rate) you're close to the 
limit of the built-in ADC.  If the typical figures given hold up, you 
will get 8-bits of absolute accuracy.

Graham.