Steps to perform serial loopback testing with Digi TransPort devices to check the integrity of the serial port:
1. Insert a loopback plug into the serial port.
Loopback plug pin-outs: RS-232 DB-25 Loop Back connector plug consists of a male DB-25 connector wired as follows:
Pin 4 connected to pins 22 and 5 (RTS to RI and CTS)
Pin 2 connected to pin 3 (TxD to RxD)
Pin 20 connected to pins 6 and 8 (DTR to DSR and DCD)
RS-232 DB-9 Loop Back connector consists of a male DB-9 connector wired as follows:
Pin 8 connected to pins 7 and 9 (CTS to RTS and RI)
Pin 3 connected to pin 2 (TxD to RxD)
Pin 4 connected to pins 6 and 1 (DTR to DSR and DCD)
RS-232 RJ-45 Loop Back connector consists of a single 8 pin RJ-45 plug wired as follows:
2. Use telnet to connect directly to the serial port. By default 4000 is the first serial port, with 4001 being the second serial port, etc..
Pin 1 connected to pin 8 (RTS to CTS)
Pin 3 connected to pin 6 (TxD to RxD)
telnet (IP_address_of_Digi_TransPort) 4000
Once CONNECTED, any data typed on the telnet session will be displayed twice. For example, the following shows a telnet connection to the first serial port on a unit with the IP address of 192.168.1.1. Once connected, the word hello is being typed:
telnet 192.168.1.1 4000
Removing the loopback plug will not display data typed in the telnet session.
To disconnect from telnet issue Control-] Enter, then type quit at the telnet prompt.