RS232 v 20ma (was: SGI Hardware Developer Handbooks available

From: Fred Cisin <cisin_at_xenosoft.com>
Date: Thu Oct 7 14:02:15 1999

The original IBM PC (NOT CLONE!) Serial port card was nominally
switchable to be used as either RS232 OR 20ma current loop!

--
Fred Cisin                      cisin_at_xenosoft.com
XenoSoft                        http://www.xenosoft.com
2210 Sixth St.                  (510) 644-9366
Berkeley, CA 94710-2219
On Thu, 7 Oct 1999, John Foust wrote:
> 
> 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:
> >Hello John and Christian,
> >
> >  I was referred to you by Don Robert regarding connecting an ASR 33 to a
> >Microcomputer RS232 Serial COM port.  Any help you can give me would be
> greatly
> >appreciated.
> 
> 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

Received on Thu Oct 07 1999 - 14:02:15 BST