I just tried to answer a question from someone on the Greenkeys mailing list, regarding interfacing an ASR-33 to RS-232. My answer is below. I hope I got it right. - John At 11:30 AM 10/7/99 -0400, Barry Hall wrote: greatly The ASR-33 usually has what's referred to as a "20 milliamp current loop" interface. It's not RS-232. You can buy converter boxes from places like <http://www.blackbox.com/>, like the one at <http://catalog.blackbox.com/blackbox/templates/blackbox/class13itemgroup598 guest.asp?param=95&ig_id=598&title=High%2DSpeed+RS%2D232%26lt%3B%26gt%3BCurr ent%2DLoop+Interface+Converter&related=>. There's an explanation at <http://telebyteusa.com/catalog/appnotes/a65a.htm>, <http://www.mouse.demon.nl/ckp/serial/cl.htm>, <http://telecom.tbi.net/data-if.html> and <http://www.bb-elec.com/techlibr.asp>. I'm sure someone has a web page with a homebrew conversion between current loop and RS-232. The voltage levels and swings aren't the same, so it's not just a matter of wiring. The circuit at <http://www.ibhsoftec.de/english/screenshots/current_loop_converter.html> might be right. - John