A/D Conversion Clock Select bits confussion ..

[gunayburak]

Thanks for your answers but I still do not understand something .. Which one of these oscillator settings should be chosen for a robust operation .. Or in other words , for a "classic proper" operation ... What I understand from your explanations is that I can choose any of these settings non regarding if the OSC is internal or external ...

As far as I know the Frc stands for internal oscillator ... Please correct me If I'm wrong at this point .. So If I choose 4MHZ with PLL operation , I'm running it with 32 MHZ internal oscillator which is also called the internal RC osc block , so in this case I should go with Frc for a more accurate conversion ... or with Fosc/32 or Fosc/2 for a faster conversion ... Right ?

[aratti]

32 MHz is a too high frequency to obtain a good ADC reading. The minimum TAD is 1.6 us and If you set fosc/64 you will get a TAD of 2 us and you are barely inside the correct timing. Since you will be in the low end side as far as the TAD value is concerned. Dropping your fosc to 16 MHz with the same setting you will have a TAD of 4 us which is much better than 2 us.

Cheers
Al.