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KB01171 - How to set up and troubleshoot RS232 connections through extenders passing commands through their outputs.

SKU: AT-UHD-EX-70C-KIT, AT-UHD-EX-100CE-KIT, AT-UHD-EX-100CEA-KIT or any other RS232 pass-through capable device.

Subject: How to set up and troubleshoot RS232 connections through extenders passing commands through their outputs.

Set up:

Confirm the commands you need to send the display. Most display manufacturers include commands in their manuals or offer the commands on their support pages. Note and port settings and any required settings that need to be enabled on the display/projector for it to accept RS232 commands. Next, connect the RS232 pins of your controller or PC to the appropriate pins on the Atlona product. Most extenders have the following RS232 pin arrangement:

Since the extenders merely pass through RS232 data, as an example, the RX pin on your control system would go to the RX pin on the extender, the TX pin to the TX on the extender and ground to ground.

You do not have to worry about setting the extenders to a specific baud rate as they will pass any commonly used baud, but do set your control system to the appropriate settings.


  • Launch your favorite serial program, or use the following serial program for PC's and serial program for MAC
  • Connect your RS232 to serial cable and establish a connection with your PC
  • Set your port settings to match your displays requirements.

Example: If using HTerm, your connection will look like so:


*Please note, port #’s and other settings may change*

  • You should see the following message in the bottom right corner of the program:


  • Once properly connected, try sending a command through the extenders to toggle power on/off on the display:


  • If the command is properly sent and received you should see the following:


  • If you successfully toggle power on the display, you are properly connected via RS232
  • If you do not have success, check your serial connection with the extenders. It’s possible the TX and RX pins need to be swapped or a null modem adapter needs to be installed. Please try flipping the TX and RX pins or installing null modem adapter. If this does not help, try another USB to serial cable and another USB port on your PC (check port settings via Device Manager as they may have changed).
  • Another method to test communication is to simply toggle power on the display whilst connected via RS232 and monitor any feedback received via the serial program:


  • If you see feedback whilst toggling power but not when sending commands to the unit, this implies that the RX and GND pins are in incorrect positions. Please swap them and see if commands pass.

If you continue to have RS232 issues, try shorting the TX and RX pins on the receiver extender unit and send any command you wish. If you see that command get sent back as “received” data then this means the Atlona extenders are passing data correctly and there is an issue with your display accepting commands. It is recommended you connect your PC directly to the display and attempt to send commands directly.

If you do not get feedback from the Atlona extenders with their TX and RX pins shorted on the receiver unit, when sending a command then this can imply there is an issue somewhere in the signal path. This can be with the USB to RS232 cable not passing data or an issue with the extenders themselves. To test the USB to serial cable, you can short the TX and RX pins (typically labeled as pins 2 and 3) and send a command through the serial program. If you see the command you sent come back, this implies the USB to serial cable is good. If you have properly connected the TX pin on the cable to the TX pin on the Atlona and the RX to RX,  and are still unable to pass RS232 data, while video does work, this means  there may be an issue with your extenders.

Please contact Atlona Technical Support for further assistance.

Article ID: KB01171

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