Pins 4, 5 are not used.Short-circuited inside.
ER(DTR)Send request (Data Terminal Ready)
CD(DCD)Carrier Detection
SG(Signal Ground)
DR (DSR) Send enable (Data Set Ready)
CS (CTS) Send enable
RS (RTS) Send request
RD (RXD) Receive data
SD (TXD) Send data
FG Frame ground
Pin No. Function
1 Frame ground
2 Send data (232ADP to RS232C device)
3 Receive data (RS232 device to 232ADP)
4 • 5 Not used
6 Shows RS232C device is ready to receive
7 Signal ground
8 On when carrier is detected for data reception
20
Signal requesting preparation for data
sending to RS232C device.