RS449 Serial Port Connector Pin Layout

RS-449 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.

RS449 is a high speed digital interface - unlike RS232 which uses signals with reference to ground, RS449 V.11 receivers look for the difference between two wires. By twisting the two wires and making a "twisted pair" any stray noise picked up on one wire will be picked up on the other, because both wires pick up the same noise the RS449 differential interface just shifts in voltage level with reference to ground, but does not change with respect to each other. The receivers are only looking at the difference in voltage level of each wire to the other not to ground.

The following document describes the functions of the pins on the RS449 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.

RS449 9 Pin connector (DB-9)

1	GND	Shield
2	SSR	Secondary Receiver Ready
3	SSD	Secondary Send Data
4	SRD	Secondary Receive Data
5	SG	Signal Ground
6	RC	Receive Common
7	SRS	Secondary Request To Send
8	SCS	Secondary Clear To Send
9	SC	Send Common

RS449 37 Pin connector (DB-37)

1	GND	Ground
2	SRI	Signal Rate Indicator
3	-	Reserved
4	TDA	Transmit Data A
5	TTA	Transmit Timing A
6	RDA	Received Data A
7	RTSA	Request To Send A
8	RTA	Receive Timing A
9	CTSA	Clear To Send A
10	LL	Local Loopback
11	DMA	Data Mode A
12	DTRA	Data Terminal Ready A
13	RRA	Receiver Ready A
14	RL	Remote Loopback
15	IC	Incoming Call
16	SF/SR	Select Frequency/Select Rate
17	TTA	Terminal Timing A
18	TMA	Test Mode A
19	GND	Ground
20	RC	Receive Common
21	-	Not Connected
22	TDB	Transmit Data B
23	TTB	Transmit Timing B
24	RDB	Receive Data B
25	RTSB	Request To Send B
26	RTB	Receive Timing B
27	CTSB	Clear To Send B
28	TIS	Terminal In Service
29	DMB	Data Mode B
30	DTRB	Data Terminal Ready B
31	RRB	Receiver Ready B
32	SS	Select Standby
33	SQ	Signal Quality
34	NS	New Signal
35	TTB	Terminal Timing B
36	SB	Standby Indicator
37	SC	Send Common