よく忘れるのでメモ。

Direction   -------------------- 9Pin   ---------------------- 25pin    ------意味
   OUT←    SD  Send Data           3   TxD  Transmitted Data      2    送信
 →IN       RD  Received Data       2   RxD  Received Data         3    受信
   OUT←    ER  Equipment Ready     4   DTR  Data Terminal Ready  20    自局接続
 →IN       DR  Data set Ready      6   DSR  Data Set Ready        6    相手局接続
   OUT←    RS  Request to Send     7   RTS  Request To Send       4    送信要求
 →IN       CS  Clear to Send       8   CTS  Clear To Send         5    送信可能
 →IN       CD  Carrier Detect      1   DCD  Data Carrier Detect   8    搬送波検出
            SG  Signal Ground       5   GND  common GrouND         7    信号接地
 →IN       CI  Calling Indication  9   RI   Ring Indicator       22    着呼