DB9 serial (RS232) loopback. Pinout and signals for building a serial port loopback (CheckIt)

The PC loopback plug is a useful diagnostic tool. The loopback plug connects serial inputs to serial outputs so that the port may be tested. There is more than one way to wire up a loopback plug - but this is the most common. Used to verify that a port is working. This one works with CheckIt.

DB9 pin D-SUB male at the DTE (Computer)
DB9 pin D-SUB male (at the computer)

Name Pin Pin Name
CD
1
6
DSR
CD
1
9
RI
RXD
2
3
TXD
DTR
4
6
DSR
RTS
7
8
CTS