>If you send a value '0x00' and then '0xFF' to a port, do all the bits change at the same time ? I'm assuming the answer is yes to this one... No, all the bits don't change at the same time. I had some problems with this in the past... -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics