Hi, I wrote: >Then I realised that for this poly ( might differ for others ) >it was quite easy to just skip the tables and calculate the output >directly: Which is not enterily correct as it was actually Scott who posted some code to this affect, sorry Scott :) my memory eludes me at times. Anyway just meant to summarize the birth of the crc-16 17 instr. snippet. /Tony -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.