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In article <4e5stp$95g@news.cc.utah.edu>, gf0570@cc.utah.edu, says...
>
>Hi everyone:
>        We are tring to connect several test equipment to a computer.
 Someone
>suggested to use RS-485 for the simplicity and long range. 
RS 485 is good if you need high speed ~500k-2m baud. The book you need 
is the EIA spec for RS-485, part of a very large EIA book that covers 
all their comm specs. 	Try the Elect engineering library there if you 
have one there

In article <4e5stp$95g@news.cc.utah.edu> gf0570@cc.utah.edu (gang fang) writes:
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>From: gf0570@cc.utah.edu (gang fang)
>Newsgroups: comp.dcom.lans.misc,comp.dcom.modems
>Subject: Books on RS-485?
>Date: 24 Jan 1996 18:14:17 GMT
>Organization: University of Utah Computer Center
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>Hi everyone:
>        We are tring to connect several test equipment to a computer. Someone
>suggested to use RS-485 for the simplicity and long range. We have no
>experience with this technology. Can someone point us to the right direction
>for this. Is there any book written on this, where is a good place to get
>information on hardware and software related to RS-485 or other low cost
>interconnection methods?
>        Thanks in advance for any information.

>-GF-

Hello if your looking for some RS-485 serial communications cards, you might 
want to try a Connect Tech Serial card!! For more information please see my 
.sig .

kam
Karl A. Morant     |  Phone  1 519 836 1291  |  email  karl@connecttech.com
Tech Support       |  Fax    1 519 836 4878  |  email  support@connecttech.com
Connect Tech Inc   | *bbs    1 519 836 5848  |  ftp    ftp.connecttech.com
Guelph, ONT CANADA | *     login as bbs      |  www    www.connecttech.com
                        

I am familiar with RS-485 from the process control and instrumentation
world.  It is commonly used to connect multiple "field" instruments or
devices to a "control" device.  

RS-485 only sets the hardware and electrical standards as far as I
know.  Using copper wires, typically two twisted pairs of wires are
used (4 wires total).  One pair is designated as the transmit, or TX,
from the main control device.  The other pair is the receive, or RX,
which carries data from the field devices back to the controller.
The electrical signals are bipolar, plus and minus 10 volts if I
remember correctly.  The field devices are placed in parallel, across
the link, to establish a "bus" topology.  Each field device is typically
addressable from the controller; the controller sends out a wake up
signal with the address of the desired field device.  All devices hear
the address and the correct one responds back by placing its data on
the RX twisted pair line.  I remember that the electrical spec. places
a limit of about 6000 feet on the total length of the link.  There
are 120 ohm terminating resistors on each end of the link to suppress
pulse reflections.  I have also used convertors which take the copper
RS-485 link and put it onto two fiber optic strands (TX and RX).  
Multiple convertors can be bussed together on the copper side to appear
as a single RS-485 circuit, with multiple fiber links going out to 
field instruments in radial fashion (star topology).  I currently have
a distributed industrial control system linked together in this manner.

Hope this gives you some information for your application.

Best Luck with your project, Bill