9 PIN-connector 25 PIN-connector Name Dir Description 
1               8  CD  input Carrier Detect 
2               3  RXD input Receive Data 
3               2  TXD output Transmit Data 
4              20  DTR output Data Terminal Ready 
5               7  GND -- System Ground 
6               6  DSR input Data Set Ready 
7               4  RTS output Request to Send 
8               5  CTS input Clear to Send 
9              22  RI  input Ring Indicator 


RTS logic on  (1) : Voltage between RTS & GND approx. -11V
RTS logic off (0) : Voltage between RTS & GND approx. +11V

DTR logic on  (1) : Voltage between DTR & GND approx. -11V
DTR logic off (0) : Voltage between DTR & GND approx. +11V

