It seems a little surprising that this is such a big issue. A reasonable value resistor to +5 or ground (depending on which is the correct idle stat= e for serial TTL, I forget) should do the job just fine. I would suggest something like 10K, which almost any reasonable signal source can override. Assuming a 5V supply you would have need 0.5 ma of current draw to pull it to the opposite rail.=20 -- Bob Ammerman RAm Systems -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of KPL Sent: Tuesday, April 15, 2014 3:01 AM To: Microcontroller discussion list - Public. Subject: Re: [EE] noise-proofing open serial interface lines Seems like my english and description skills have failed, as usually. That interface is left there just for very rare occasions when some reconfiguration is needed, like RTC adjustments or irrigation rescheduling. All the other time there will be absolutely nothing connected, and i just want make sure those lines will not pick up a lot of noise at that time, as that will cause controller to try to parse what it has received. No long wires, just a short cable to a connector in the same housing. Even if lantronix will be permanently connected there for some reason, it will be located in the same box, as ethernet will be used for remote access= .. On 12 April 2014 11:46, William "Chops" Westfield wrote: > On Apr 7, 2014, at 2:05 PM, Jesse Lackey wrote: > >> If possible, you could use RS-485 instead of TTL-level. > > Real rs232 would be better than TTL, too. Aside from the wider=20 > voltage margins, I think real rs232 has somewhat controlled impedance. =20 > And most modern converter chips will include some ESD protection as well. > > BillW > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive=20 > View/change your membership options at=20 > http://mailman.mit.edu/mailman/listinfo/piclist -- KPL -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .