9-Pin (AT) Serial Port Connector

 

Pin	Description	Signal	Direction to/ from Card
1	Carrier detect	CD	in
2	Receive data	RD	in
3	Transmit data	TD	out
4	Data terminal ready	DTR	out
5	Signal ground	SG	-
6	Data set ready	DSR	in
7	Request to send	RTS	out
8	Clear to send	CTS	in
9	Ring indicator	RI	in

 

25-Pin (PC, XT, and PS/2) Serial Port Connector

 

Pin	Description	Signal	Direction to/ from Card
1	Chassis Ground	-	-
2	Transmit Data	TD	Out
3	Receive Data	RD	In
4	Request to Send	RTS	Out
5	Clear to Send	CTS	In
6	Data Set Ready	DSR	In
7	Signal Ground	SG	-
8	Carrier Detect	CD	In
9	(+) Transmit Current Loop Return	-	Out
11	(-)Transmit Current Loop Data	-	Out
18	(+) Receive Current Loop Data	-	In
20	Data Terminal Ready	DTR	Out
22	Ring Indicator	RI	In
25	(-) Receive Current Loop Return	-	In

Pins 9, 11, 18, and 25 are used for a Current Loop interface only.

Current Loop is not supported on the AT Serial/Parallel Adapter or PS/2 systems

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Page updated 98/07/14