Jan-Erik Soderholm wrote:

>Matthew Miller wrote :
>
> =20
>
>>On Sun, Feb 13, 2005 at 01:40:13PM +0100, Jan-Erik Soderholm wrote:
>>   =20
>>
>
> =20
>
>>>But then, how do you connect the 32 "nodes" on a single
>>>RS485 "network" ? (32 according to the original spec, newer
>>>hardware can handle a higher number of concurrent nodes
>>>due to higher "off" impedance in CMOS then in the original
>>>bipolar devices when the spec was written...)
>>>     =20
>>>
>>Well, those nodes just connect to the same twisted pair ;)=20
>>The trouble is deciding when you can transmit.
>>   =20
>>
>
>Now, how do you transmit *at all* if the other 31 nodes
>are activily holding the line low (or high or whatever) ?
>
>Never mind...
>
>Jan-Erik.
>
>
>
> =20
>
To clear this up....

The RS-485 transceiver drives a differential pair. When active it put=20
out a 0/1 on the pairs or a 1/0  for a zero or a one. When the=20
tranceiver is inactive it tristate and output floats. The receiving part=20
of the transceiver can of course still be active.


A variant is to send on one pair and receive on one pair. Same=20
electrical specs. but this is RS-422.

Regards
/Ake

--=20
 ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se     =20
Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org


--=20
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