# EIA-449 (RS-449)

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

(at the DTE)
(at the DCE)

CORRECT?

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

Source:
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