Jinx wrote: >/RING0 on the DB9 is at 0V, and shows positive-going activity On pin 9 of the DB9 connector on the black plastic box? I'd expect that to be a bipolar (RS-232 style) signal rather than a logic-level signal. As such, 0V is an undefined state (should be < -3V for a "one" and > +3V for a "zero", IIRC). Many receivers will interpret 0V as a "one", but there's not much voltage margin on that. Is it possible that the negative voltage generator on the MAX232-like chip inside the box is not working? If so, then this might also cause some "one" bits on its serial data output to be missed by your receiver at the other end, especially at higher data rates when line capacitance slows the transitions. This seems to fit with the symptoms that you're seeing: some "one" bits in the data turning into zeroes. On the other hand, I may be barking up completely the wrong tree... -- Ian Chapman Chapmip Technology, UK -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body