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From: rainer@boulder.Colorado.EDU (Rainer Malzbender)
Newsgroups: sci.electronics
Subject: Re: Anybody know of line drivers for EIA485,422?
Message-ID: <25171@boulder.Colorado.EDU>
Date: 24 Aug 90 21:56:17 GMT
References: <28801@netnews.upenn.edu>
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In article <28801@netnews.upenn.edu> asilver@grad1.cis.upenn.edu (Andy Silverman) writes:
>I'm working on a project (A DMX512 compatible dimmer controller) which
>requires all data transmission to conform to EIA-485, which is for
>most practical intents and purposes the EIA(or RS)-422 spec.  This is
>a balanced line with a voltage differential between the two lines of
>at least 1.5V into 54 ohms. (EIA-422 is 2V into 100 ohms, >1/2 open
>circuit V, according to the EIA-486 spec., so anything that conforms
>to EIA-422 should be OK for 485, right?)
> 

According to my National databook, RS422 and RS485 are slightly different.
RS422 only allows one driver and ten receivers per line, while RS485
allows 32 drivers and 32 receivers. RS485 also has an extended common
mode range. I guess if you're not doing true multipoint communications
the two are probably interchangeable. Part numbers from National are
DS3695-DS3698 and DS75176 for transceivers. In the near future I plan on
using these to design a multipoint "smart house" system with little
microprocessor modules distributed throughout the house on RS485.

You can't get these chips from Jameco, though, but you can order stuff
from distributors or National sales offices.

--
Rainer M. Malzbender                          Technology recapitulates biology.
Dept. of Physics                (303)492-6829       rainer@hibachi.colorado.edu 
U. of Colorado, Boulder, USA                  malzbender%opus@vaxf.colorado.edu