At 05:01 AM 6/18/2010, Olin Lathrop wrote: >Twisted pair ethernet is a example of isolated differential signals where >there is not common reference conductor. Completely agreed. But: they use transformers. That's completely different from using something like the 65lbc176 differential transceivers that I have been talking about. One of the main differences is that you can transmit very low frequency (or DC) signals using the differential transceivers I mentioned. The transformers used in twisted-pair Ethernet won't pass low frequency or DC signals. But - I think that we are talking apples and oranges here. The original poster was, I'm pretty sure, talking about standard RS-485 or possibly RS-422 type communications. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist