RS-485 net (was: Re: moxa multiport serial cards)

[Boris Samorodov]

On Fri, 13 Oct 2006 12:14:37 +0100 Philip M Brown wrote:

Please, keep CC to freebsd-questions for archieves sake so others may
find that info. And, please don't top-post. Thanks for your patience.

> On Fri, 2006-10-13 at 15:06 +0400, Boris Samorodov wrote:
> > 
> > If your hardwares use RS-485 ports than you can connect (up to
> > 32/64/.. -- depends on port chips) to RS-485 net and control them
> > through one master device (one RS-485 port at your server). Setting up
> > an RS-485 net has it own tips and tricks which you may find at
> > Google. 

> ok, thanks for super quick response. 

You are welcome. ;-)

> it seems my hardware i need to connect to is rs-232.

You may check the documentation for your hardware.

> however as I am bemused with 485 can you please explain, is it as i
> expected, where one of the db25 leads from the card could the be split
> into multiple devices or do i need another box in between.

All RS-485 devices should be connected to one line (2/3/4/5 wires
possible). Maximum number of those devices depends on their chip
properties. Maximun line length (as for standart) is 1200 meters at
maximum speed. The line should be terminated with 120 Ohm resistor at
both ends. Only one device is a master and should initiate a
conversation. All others are slaves and only answer when asked. Slave
devices are addressed by their net address. And so on...

More info is available at Google.


WBR
-- 
Boris Samorodov (bsam)
Research Engineer, http://www.ipt.ru Telephone & Internet SP
FreeBSD committer, http://www.FreeBSD.org The Power To Serve