General assignment of V.24 (RS-232C) connectors
DB25 - male (plug) DB25 - female (socket)
2 TxD 2 RxD
3 RxD 3 TxD
4 RTS 4 CTS
5 CTS 5 RTS
6 DSR 6 DTR
7 GND 7 GND
8 DCD 8 DCD
20 DTR 20 DSR
22 RI 22 RI
DB9 - male (plug) DB9 - female (socket)
1 DCD 1 DCD
2 RxD 2 TxD
3 TxD 3 RxD
4 DTR 4 DSR
5 GND 5 GND
6 DSR 6 DTR
7 RTS 7 CTS
8 CTS 8 RTS
9 RI 9 RI