RS422 Serial Port Connector Pin Layout

RS-422 is a serial communications standard that provides asynchronous communication capabilities, such as hardware flow control, software flow control, and parity check. It has been widely used for decades. Unlike RS-232, RS-422 is capable of data transmissions over long distances (up to 4000 Feet). Because RS-422 is using 2 wires for each signal, it is less sensitive to noise.

The following document describes the functions of the pins on the RS422 9 and 37 pin Sub-D connectors used in serial communications. The pins in the images are as viewed from the pin side (not the solder or printed circuit board side). The male sockets are used on the DTE (Data Terminal Equipment ) or PC side. The female sockets are on the DCE (Data Communication Equipment ) or Modem Side.

Using the ActiveXperts Serial Port Component you can send and receive data and control the RS422 port.

RS422 9 Pin connector (DB-9)

1	TXD-	Transmitted Data -
2	TXD+	Transmitted Data +
3	RTS-	Request To Send -
4	RTS+	Request To Send +
5	GND	Ground
6	RXD-	Received Data -
7	RXD+	Received Data +
8	CTS-	Clear To Send -
9	CTS+	Clear To Send +

RS422 37 Pin connector (DB-37)

1	GND	Ground
2	SRI	Signal Rate Indicator
3	-	Reserved
4	SD	Send Data A
5	ST	Send Timing A
6	RD-	Received Data A
7	RTS	Request To Send A
8	RR	Receiver Ready A
9	CTS	Clear To Send A
10	LL	Local Loopback
11	DM	Data Mode A
12	TR	Terminal Ready A
13	RR	Receiver Ready A
14	RL	Remote Loopback
15	RL	Remote Loopback
16	SF/SR	Select Frequency / Select Rate
17	TT	Terminal Timing A
18	TM	Test Mode
19	GND	Ground
20	RC	Receive Common
21	GND	Ground
22	/SD	Send Data B
23	/ST	Send Timing B
24	/RT	Receive Timing B
25	/RS	Request To Send B
26	/RT	Receive Timing B
27	/CS	Clear To Send B
28	IS	Terminal In Service
29	/DM	Data Mode B
30	/TR	Terminal Ready B
31	/RR	Receiver B
32	SS	Select Standby
33	SQ	Signal Quality
34	NS	New Signal
35	/TT	Terminal Timing B
36	SB	Standby Indicator
37	SC	Send Common