This content is not available in your preferred language.

The content is shown in another available language. Your browser may include features that can help translate the text.

Connect and Configure a 2-Wire Device with an RS-485 Serial Port

Updated Jan 11, 2019

Reported In


  • RS-485
  • RS-232
  • Serial Cable

Issue Details

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?


RS-485 is, by default, set up for four-wire communication. Two pins send data (TXD+ and TXD-) and two pins receive data (RXD+ and RXD-) as differential signals as shown below.

To connect a 2-wire device, you must connect the 2-wire device's send pin (TXD) to both TXD- and RXD- and the device's receive pin (RXD) to both TXD+ and RXD+. In the image above, jumper wires would be placed between pins 4 and 8, and between pins 5 and 9.

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.


Not Helpful