1. Plug a Loopback Plug into the serial port to be tested. A loopback plug is generally shipped with Digi products which can use them, but if you need to make one, please see the following article:How to make an RS-232 loopback plug
2. From the Windows CMD or a Unix/Linux "root" prompt, telnet (or SSH) to the IP address of the Digi device server.
If additional information is needed on how to use or where to get a Telnet client, please refer to this article:HOW TO: Access and capture output from the CommandLine Interface (CLI) of a Digi network-connected product using Telnet or SSH3. Login at the commandline interface (CLI). Digi's common default user login is:user: rootpass: dbps
4. From the CLI prompt, set the port to a printer device type (we use port 1 in our example):
set port dev=prn range=1kill tty=1
5. Enter connect 1 (one) to connect to the first serial port. The following message appears:
Set escape character to ^[
6. Start typing characters on your keyboard. The characters you type should echo back and be displayed on your PC monitor (once). If you remove the loopback plug from the port and keep typing, you should not see any data on your screen.
To disconnect from the port, type: Ctrl-[ . (Control left-square bracket, followed by a period), then [Enter], and repeat the procedure for any other ports which need testing (don't forget to move the Loopback plug to the port you're testing!)
Alternatively, this can also be tested using reverse telnet to the TCP socket of the port directly, by issuing the following command from either the DOS/Unix prompt or the Digi unit command prompt:telnet (IP_of_Digi_unit) 20##Where 20## represents the default TCP port number. For port number 1, use 2001; for port number 2 use 2002; etc. Any data typed in the telnet session will be echoed on the screen.To disconnect from telnet, issue <Ctrl>-] and type quit at the telnet prompt.Note: If the Digi device has serial DIP switches (i.e. an MEI model), they must be configured for RS-232 or RS-422. The bundled loopback plug will not work if the DIP switches are configured for RS-485.