Why the realport keeps returning character 'T'?

I am using Digi TS16 server and configured to use realports. The port keeps returning character ‘T’ no matter the physical port is connected to another device or not.

What is the meaning of that ‘T’ character?

The letter T could point to a mismatch of the settings between the serial port and the attached device. I recommend checking the baud rate, stop bits, character bits and parity settings to ensure the match.

Also, it might be a good idea to run a loopback test to make sure the port is functional on the Digi unit: