Computer Interfacing
Discussions about interfacing and electronics
 

RS-485 network configuration


 

       Computer Interfacing Forum Index -> RS422 and RS485
Author Message
Gooli
New User



Joined: 19 May 2010
Posts: 2


May 19, 2010 4:25 pm

I have a 485 network (card reader access system) consisting of 15 card reader nodes, and one central node which makes all decisions for accessing doors.

Problem is, the cable lenght is too great, and the last two nodes does not get a good connection.

At the moment the central node is located at one end of the daisy chain. Would I benefit from relocating it to the middle of the chain, (still keeping the 100 ohm resistors at the ends), and by that shortening the distance from card reader nodes to the central node, or would there be some disadvantages?
lammert
Site Admin



Joined: 13 Mar 2007
Posts: 146
Location: Netherlands and Kazakhstan

May 20, 2010 6:28 am

Repositioning the nodes may not be the best solution, because the cable length effectively stays the same, and therefore signal distortion will not change much. You may be lucky though, if the end-nodes do not communicate with each other and only with the centrally positioned master.

Another option is to lower the baud rate, as lower speeds on the network may give the receivers more time to settle at the correct signal level.
Gooli
New User



Joined: 19 May 2010
Posts: 2


May 20, 2010 1:42 pm

I am almost certain that the card reader nodes only communicate with the master node. The only thing I can think of would be if they had some ongoing traffic between each other concerning "who's turn it is to speak" so to say. How does a 485 system communicate without the nodes colliding when communicating with each other?
greendriv
New User



Joined: 12 Sep 2010
Posts: 1
Location: China

Sep 12, 2010 12:49 pm

As ammert said, another option is to lower the baud rate, as lower speeds on the network may give the receivers more time to settle at the correct signal level.

:-) This solves my problem I met a few months ago. Thank you, ammert.

       Computer Interfacing Forum Index -> RS422 and RS485
Page 1 of 1



Running on php BB © 2001, 2009 php BB Group
   Lammert Bies     Interfacing     Sitemap     Forum