This Document is not yet Rated

Rate this Document

How do I Connect and Configure a 2-Wire Device With RS-485

Hardware: Instrument Connectivity Other>>USB>>USB-485/4

Problem:
I have a 2-wire serial device (RS-232) that I want to connect to an RS-485 serial port. Since RS-485 communication is usually 4-wire, how do I connect it and how do I configure Windows to communicate with the device?

Solution:
RS-485 is by default setup for four wire communication. Two pins send data (TXD+ and TXD-) and two pins receive data (RXD+ and RXD-) as differential signal as shown below.
To connect a 2-wire device, the 2-wire device's send pin (TXD) must be connected to TXD- and RXD- as well as the device's receive pin (RXD) connected to TXD+ and RXD+.

Because the send and receive pins are shorted together on the RS-485 COM port, the COM port must be configured to communicate in 2-wire half-duplex mode. To do this, follow the steps below:

1. Go to Windows Control Panel
2. Click on System
   
3. In the system menu choose the Hardware tab.
4. Click on Device Manager
5. Expand the Ports menu and right-click on the RS-485 serial port in use and choose Properties.
6. Choose the Port Settings tab and choose Advanced.
7. Choose the 2-Wire Auto setting from the Tranceiver Mode drop-down menu.
   

Related Links:
Product Manuals: Serial Quick Reference Guide
KnowledgeBase 17M6L0TI: What Are the Different Transceiver Modes on the NI RS-485 Serial Cards?
KnowledgeBase 34FFR7NB: How Can I Self-Test My PCI-485i-2 to Check That All Ports Work?

Attachments:





Report Date: 09/25/2006
Last Updated: 04/01/2008
Document ID: 41OICGAC

Your Feedback!	Poor  |  Excellent							Yes	No
Document Quality?							Answered Your Question?
	1	2	3	4	5
Document needs work? Please tell us why.
Please Contact NI for all product and support inquiries.