Atlona Help Center

KB01195 - How to troubleshoot an RS232 cable (in order to ensure it works with controlling Atlona devices)

SKU: Any Atlona device with RS232 support

Subject: How to troubleshoot an RS232 cable


Considering a typical RS232 control scenario, you have a device that sends RS232 commands (let’s call this an “RS232 sender”) and a device that you intend to control with RS232 (let’s call this an “RS232 receiver”) as well as an Atlona device that either pass RS232 (i.e. HDBaseT extenders) or that can send RS232 on its own (AT-HDVS-200 system). With this, there are multiple variables/potential points of failure to consider whenever RS232 is not working:

  • There is an RS232 cable coming from the RS232 sender that can either be terminated in DB9 or bare wire
  • If this cable is terminated with a DB9 end, it will then need a bare wire connection for most Atlona device. This can be another cable which is also a variable
  • The Atlona device(s) either have a bare wire RS232 connection or a DB9 plug. If you use extenders, you will have an RS232 plug on both components.
  • The device you intend to control most likely has its own DB9 plug and will need a bare wire to DB9 cable from the Atlona’s output.

This means you can have a total of 4-6 connections, either one of which can have an issue in passing RS232 which can prevent the entire system from working. Luckily, troubleshooting RS232 is fairly simple:

  1. To test the cable sending RS232 commands into an Atlona device (or from the Atlona device), simply short the TX and RX pins of the cable with a metallic object, and use a serial program (or Atlona’s feedback verify feature) to see if sending any RS232 data allows you to see that as feedback. If you send “HELLO” and immediately see “HELLO” echoed back, this means the cable is most likely able to send RS232 and thus appears to be working correctly.
  2. To test the connections made at Atlona HDBaseT extenders with RS232 pass-through, simply confirm that the TX pin of your controller is going to the TX pin on the Atlona, RX to RX and Ground to Ground (this is a pass through RS232 connection). For devices such as matrices or CLSO switchers (or any device where RS232 commands must be sent within a “zone” command such as “RS232zone5”), confirm that the TX pin of your control device is going to the RX pin on the Atlona and the RX pin of the control device going to the TX of the Atlona, ground will be connected to ground.
  3. If you don’t get any control through your Atlona device, please make sure you can pass audio/video. If those don’t pass either, there may be issues with the device connections (i.e. a faulty CAT cable can prevent HDBaseT extenders from talking to each other and passing commands). See this article for more info on troubleshooting extenders that don’t have stable video/audio playback.
  4. To check the cable being used to come out of the Atlona device (i.e. a bare wire to DB9 cable) short-circuit the TX and RX pins of this cable and send a command through the Atlona device. Are you able to see the command as feedback on the RS232 sender? If so, this appears that the cable being used on the output is working.
  5. To check the RS232 cable going into your device. See if you can send an RS232 command directly from your RS232 sender or a computer and verify if the device responds. If so, the cable you are using appears to be functional.

If you are getting video/audio playback through your Atlona device but RS232 still doesn’t pass and you have performed the steps above, please contact Atlona Technical Support for more help.

Article ID: KB01195

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