Apple III SERIAL PORT Cable Printer Connector Frame Ground ............(FG)...... 1 <-----> 1.....(FG) Transmit Data (Tx) ..... 2 <-----> 3.....(Rx) Receive Data (Rx) ..... 3 Request to send (RTS) .... 4 Clear To Send (CTS) .... 5 Data Set Ready (DSR) .... 6 <-----> 20....(DTR) Signal Ground ...........(SG)...... 7 <-----> 7.....(SG) Data Carrier Detect (DCD) .... 8 Secondary Clear To Send (SCTS) ... 19 Data Terminal Ready (DTR) .... 20