Does ATD on 9s12 round or truncate?

[onnimikki]

Hi,

I'm trying to determine whether the binary search algorithm mentioned in the 9s12 documentation rounds or truncates signals into the analogue to digital converter (ATD).  I was reading through the MC9S12C Family Data Sheet (MC9S12C Family Rev. 1.15 7/2005) and it says "By following a binary search algorithm, the A/D machine locates the approximating potential that is nearest to the sampled potential."  There's not a whole lot of detail as to how it actually does this.  If the voltage signal corresponded to a 10bit-configured ATD output of 988.8, would it truncate it down to 988 or round up to 989?  Any pointer to an official document that explains this would be much appreciated. 

Thanks!

James

[lama]

Hi,

It depends on a few factors.

I think the AN2438 could answer your question. If you compare errors definitions defined in the data sheet with the AN and you will see what they mean, I believe, you will understand.

http://www.freescale.com/files/microcontrollers/doc/app_note/AN2438.pdf

It is good also to read, for example, A closer look at the effects of charge sharing in the

http://cache.freescale.com/files/microcontrollers/doc/app_note/AN2429.pdf

Best regards,

Ladislav