Symbols + brief description 
Transmit DATA (output) 
TXD (SD) transmits serial data of the computer outward 
Receive DATA (input) 
RXD (RD) receives data, which are supplied from the outside 
Request to transmit (output) 
RTS (R-S) request to transmit data to the computer. 
CLEAR to transmit (input) 
CTS (CS) external device would like to transmit data. 
DATA set ready (input) 
DSR (DR) external device is ready for transfer. 
Signal Ground 
SG signal mass 
Carrier Detect (input) 
CD input for the signal carrier. 
Calling indicator (input) 
CI INTERRUPT request of the external device. 
Logic volume days (output) 
Vcc supply voltage of the logic (4 to 4,7 V). 
DATA terminal ready (output) 
DTR (IT) computer is ready for datentransfer. 

For a simple data communication to another device, modem or PC with serial RS-232c interface Pin2 are to be occupied + Pin3 +Pin7. The transmission speed can take place to 34600 Baud.