Performing a COM port loopback test using PuTTY in Microsoft Windows

PuTTY is a free telnet/SSH client which can be downloaded from

To perform a loopback test on a COM port, first plug in the loopback plug into the desired port on your Digi hardware.   Loopback adapters ship with all Digi Terminal Server products.  They are small RJ-45, DB-25 or DB-9 plugs with no cable.  If a loopback needs to be made, see this Knowledge Base article:  Creating a Loopback Adapter.

Run PuTTY and fill in the appropriate serial port information:

User-added image

Any data typed will echo onto your PuTTY screen:

User-added image

If you can see the characters you typed in, the port is looping the data properly.  If the data is not seen, it may be an indication of a hardware issue.

Last updated: Jan 02, 2024

Filed Under


Recently Viewed

No recently viewed articles

Did you find this article helpful?