Pin   Function	Dir	Description
1	CD	In	Carrier Detect
2	RxD	In	Receive Data
3	TxD	Out	Transmit Data
4	DTR	Out	Data Terminal Ready
5	GND	 	signal GrouND
6	DSR	In	Data Set Ready
7	RTS	Out	Request To Send
8	CTS	In	Clear To Send



APC Smart UPS cable pinout
==========================
UPS		DB-9 Male	DB-9 Female	PC	
Signal Name	(UPS end)	(PC end)	Signal Name
TX / AC Fail	2		2		Rx, Received Data
RX / Shutdown	1		3		Tx, Transmitted Data
Common		9		5		GND

At the PC end: pins 1,4 (DCD, DTR) shorted; pins 7,8 (RTS, CTS) shorted.