pic wrote: > I'm looking at designing a multi drop comm's system for control purposes. > I have been investigating RS485, and RS422 keeps on coming up along with it, > so I know there can't be much difference between them, but what is the > difference ? They are both 5V differential (twisted pair) but RS422 is unidirectional - the drivers are always enabled (but you can have more than one receiver) whereas RS485 is bi-directional - the transmitters are tri-stated when not talking. RS485 also has better common-mode isolation specs. -- Clyde Smith-Stubbs | HI-TECH Software, | Voice: +61 7 3300 5011 clyde@hitech.com.au | P.O. Box 103, Alderley, | Fax: +61 7 3300 5246 http://www.hitech.com.au | QLD, 4051, AUSTRALIA. | BBS: +61 7 3300 5235 ---------------------------------------------------------------------------- For info on the World's best C cross compilers for embedded systems, point your WWW browser at http://www.hitech.com.au, or email info@hitech.com.au