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.

9 Pin connector (DB-9)

9 pin connector
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 +

37 Pin connector (DB-37)

37 pin connector
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