The Serial Port Connector

This is a DB9 male connector with a private pinout describe below.

Pin     Signal  Description             Direction
1       -       unswitched (+5v at 10 uA) output
2       TxD     transmit data           output
3       RxD     receive data            input
4       RTS     ready to send           output 
5       CTS     clear to send           input
6       -       reserved for future use -
7       GND     Ground
8       DCD     data carrier detect     input
9       DTR     switched (+5v at 1mA)   output

Note : DTR is high when the machine is awake. The machine is always awake when the screen is active, but even if asleep the machine will wake every minute or so to carry out various housekeeping tasks, such as checking for alarms, and at these time DTR will go high. Pin 1 will show a signal if there is power available to the machine.