rj45  db9  db25  signal  description
1     9    22    ri      ring indicator
2     1    8     dcd     data carrier detect
3     4    20    dtr     data terminal ready
4     5    7     sg      signal ground
5     2    3     rxd     received data
6     3    2     txd     transmitted data
7     8    5     cts     clear to send
8     7    4     rts     request to send