Re: [avr-gcc-list] atmega16

[Mattias Svensson]

> > > I'll like to now some details about atmega16. Can I use some pins of
> > > Port A as Analog Inputs while some others will be used as d\ igital
> > > in/out ?
> >
> > Yes, but noise may be induced on an analog input if a port A output switches 
> > levels.
>
>
> Do you mean that coupling among the same port is somehow tighter then
> coupling with pins of another port? My gues would be no, but your
> formulation provoked this question in my mind:
>
>  If one have to switch output level during the A/D conversion, are
>  there better and worse pin assignments to choose from?
>
> My choice would be to use pins which are physically far apart but
> maybe somebody knows better...

The thing is that port A uses the same power supply pin for the ADC and 
the digital IO. That means, if you switch an port pin while running an 
ADC conversion, the supply for the ADC will be bumped, and result in 
false readings.
Usually you put a filter on the analog supply for port A if you use it 
as analog input. This to filter out noise from the rest of the circuitry 
 (and the AVR itself). The filter means higher impedance and if you 
switch the digital IO it will give even larger bumps in the supply.

/Mattias S