Biasing Resistor for Rs-485 transmission line

EDAboard.com Forum Index -> PC Programming and Interfacing -> Biasing Resistor for Rs-485 transmission line

Author

Message

boogie

Joined: 07 Apr 2005
Posts: 4

07 Apr 2005 3:52 Biasing Resistor for Rs-485 transmission line

Hello.
I want to ask how to calculate biasing resistor for RS-485 transmission line.
can you give me some references or some links to solve my problem.

Thanx in advanced

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

07 Apr 2005 4:00 Re: Biasing Resistor for Rs-485 transmission line

Typical values of bias resistors are between 1kΩ and 4.7kΩ ..
I use 2.2kΩ ..
Some more info here:
http://www.hw.cz/english/docs/rs485/rs485.html
http://www.sixnetio.com/htmlhelps/sixnetkb/5a6d06e.htm

Google
AdSense
Google Adsense

07 Apr 2005 4:00 Ads

vdaniel

Joined: 08 Oct 2004
Posts: 216
Helped: 9

08 Apr 2005 9:18 Re: Biasing Resistor for Rs-485 transmission line

You can find very useful application notes for the RS485 in the National Semiconductor. www.national.com

Varuzhan

7rots51

Joined: 17 May 2002
Posts: 1427
Helped: 14

08 Apr 2005 12:19 Re: Biasing Resistor for Rs-485 transmission line

you can pull up the A line with 470 ohm to vcc=5v at one device,and pull down the B line to GND with 470R also at same device.other nodes do not need pullup and pulldown.(one node is sufficient).

But you can use 4.7K for each node and all nodes have pullup/down.