Thanks Michael. In point of fact I do not see the echoed "U", but wasn't sure if I needed to send more or look for a problem. At this point I believe that the problem is one of frequency match error. I will make some more measurements and do some more calculations and see what I can find. Nonetheless, given my inexperience with this microcontroller I can not rule out that I am overlooking something simple (and in all probability common to "newbies").