Richard: Thank you very much for your answer. I have studied the manual and it doesn't have the text you showed, surely I have an older version. (if you would have a link) Anyway, thank you. With this information I'm not quite sure about what to do except letting the define_clock at 3. The application doesn't require very fast readings but accurate. I'll read PT100 sensors and I'm now busy making the propper signal conditioner with some op amps. Indeed is a microchip circuit proposal (AN687c document) with little modifications, using the AD of the 4550 instead of an independent AD, and testing with stereo audio cable to connect the three cables between the pic circuit and the PT100 sensors. Yes it is more entertaining than TV, maybe not more than, for instance, "Obsession" movie, with Juliette Binoche (my girlfriend) and Jeremy Irons. Have a good day.