DTE to DCE straight cable
=========================
DB9 <-----------> DB25
=========================
1 CD <----------> 8 CD
2 RD <----------> 3 RD
3 TD <----------> 2 TD
4 DTR <---------> 20 DTR
5 GND <---------> 7 GND
6 DSR <---------> 6 DSR
7 RTS <---------> 4 RTS
8 CTS <---------> 5 CTS
9 RI <----------> 22 RI
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DCE to DCE crossover cable
=========================
DB9 <-----------> DB25
=========================
1 CD <---------->
2 RD <----------> 2 TD
3 TD <----------> 3 RD
4 DTR <---------> 6 DSR
5 GND <---------> 7 GND
6 DSR <---------> 6 DTR
7 RTS <---------> 5 CTS
8 CTS <---------> 4 RTS
9 RI <---------->
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