Title says it all :) I wanted to build a serial loopback plug compatible with the ancient CheckIt diagnostic tool. It wires 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.
Pinout front view:
| From | Pin | Pin | To |
|---|---|---|---|
| CD | 1 |
6 |
DSR |
| CD | 1 |
9 |
RI |
| RXD | 2 |
3 |
TXD |
| DTR | 4 |
6 |
DSR |
| RTS | 7 |
8 |
CTS |