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EIA-449 (RS-449)

Common names: EIA-449, RS-449, ISO 4902
Primary channel

37 PIN D-SUB MALE (at the DTE)
37 PIN D-SUB FEMALE (at the DCE)


37 PIN D-SUB MALE at the DTE (Computer).
37 PIN D-SUB FEMALE at the DCE (Modem).

Pin Name V.24 Dir Description Type
1   101 --- Shield Ground
2 SI 112 --> Signal Rate Indicator Control
3 n/a   n/a unused  
4 SD- 103 --> Send Data (A) Data
5 ST- 114 <-- Send Timing (A) Timing
6 RD- 104 <-- Receive Data (A) Data
7 RS- 105 --> Request To Send (A) Control
8 RT- 115 <-- Receive Timing (A) Timing
9 CS- 106 <-- Clear To Send (A) Control
10 LL 141 --> Local Loopback Control
11 DM- 107 <-- Data Mode (A) Control
12 TR- 108.2 --> Terminal Ready (A) Control
13 RR- 109 <-- Receiver Ready (A) Control
14 RL 140 --> Remote Loopback Control
15 IC 125 <-- Incoming Call Control
16 SF/SR+ 126 <-> Signal Freq./Sig. Rate Select. Control
17 TT- 113 --> Terminal Timing (A) Timing
18 TM- 142 <-- Test Mode (A) Control
19 SG 102 --- Signal Ground Ground
20 RC 102b --- Receive Common Ground
21 n/a   n/a unused  
22 SD+ 103 --> Send Data (B) Data
23 ST+ 114 <-- Send Timing (B) Timing
24 RD+ 104 <-- Receive Data (B) Data
25 RS+ 105 --> Request To Send (B) Control
26 RT+ 115 <-- Receive Timing (B) Timing
27 CS+ 106 <-- Clear To Send (B) Control
28 IS n/a --> Terminal In Service Control
29 DM+ 107 <-- Data Mode (B) Control
30 TR+ 108.2 --> Terminal Ready (B) Control
31 RR+ 109 <-- Receiver Ready (B) Control
32 SS 116 <-- Select Standby Control
33 SQ 110 <-- Signal Quality Control
34 NS n/a --> New Signal Control
35 TT+ 113 --> Terminal Timing (B) Timing
36 SB 117 <-- Standby Indicator Control
37 SC 102a --- Send Common Ground

Note: Direction is DTE (Computer) relative DCE (Modem).

Name Description Function
AA Shield Ground Also known as protective ground. This is the chassis ground connection between DTE and DCE.
AB Signal Ground The reference ground between a DTE and a DCE. Has the value 0 Vdc.
BA Transmitted Data Data send by the DTE.
BB Received Data Data received by the DTE.
CA Request To Send Originated by the DTE to initiate transmission by the DCE.
CB Clear To Send Send by the DCE as a reply on the RTS after a delay in ms, which gives the DCEs enough time to energize their circuits and synchronize on basic modulation patterns.
CC DCE Ready Known as DSR. Originated by the DCE indicating that it is basically operating (power on, and in functional mode).
CD DTE Ready Known as DTR. Originated by the DTE to instruct the DCE to setup a connection. Actually it means that the DTE is up and running and ready to communicate.
CE Ring Indicator A signal from the DCE to the DTE that there is an incomming call (telephone is ringing). Only used on switched circuit connections.
CF Received Line Signal Detector Known as DCD. A signal send from DCE to its DTE to indicate that it has received a basic carrier signal from a (remote) DCE.
CH/CI Data Signal Rate Select
(DTE/DCE Source>
A control signal that can be used to change the transmission speed.
DA Transmit Signal Element Timing
(DTE Source)
Timing signals used by the DTE for transmission, where the clock is originated by the DTE and the DCE is the slave.
DB Transmitter Signal Element Timing
(DCE Source)
Timing signals used by the DTE for transmission.
DD Receiver Signal Element Timing
(DCE Source)
Timing signals used by the DTE when receiving data.
IS terminal In Service Signal that indicates that the DTE is available for operation
NS New Signal A control signal from the DTE to the DCE. It instructs the DCE to rapidly get ready to receive a new analog signal. It helps master-station modems rapidly synchronize on a new modem at a tributary station in multipoint circuits
RC Receive Common A signal return for receiver circuit reference
LL Local Loopback / Quality Detector A control signal from the DTE to the DCE that causes the analog transmision output to be connected to the analog receiver input.
RL Remote Loopback Signal from the DTE to the DCE. The local DCE then signals the remote DCE to loopback the analog signal and thus causing a line loopback.
SB Standby Indicator Signal from the DCE to indicate if it is uses the normal communication or standby channel
SC Send Common A return signal for transmitter circuit reference
SF Select Frequency A signal from the DTE to tell the DCE which of the two analog carrier frequencies should be used.
SS Select Standby A signal from DTE to DCE, to switch between normal communication or standby channel.
TM Test Mode A signal from the DCE to the DTE that it is in test-mode and can't send any data.
  Reserved for Testing  

Contributor: Joakim Ögren

RS449 Page at Connectivity Knowledge Platform (Made IT)

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2001-06-07