EIA-449 Pinout, Signal Assignments

The EIA/TIA-449 is a general purpose 37-Position Interface for Data terminal Equipment and Data Circuit-Terminating Equipment Employing Serial binary Data Interchange

EIA-449 cabling uses EIA-422 differential pairs to send and receive data, and EIA-423 single-ended lines to send and receive control signals.

V.35/RS449 Cable Length Recommendations; The cable length will determine maximum bus speed, or the maximum transfer rate is determined by the cable length.
Length of Cable x Maximum Data Thru-put:
2Mbps data transfer out to 50 feet of cable, maximum [15 meters],
1Mbps data rates with 100 feet of cable,
512kbps to 200 feet, 256kbps to 400 feet, 128kbps to 800 feet, 56kbps to 1600 feet,
1.2kbps out to a maximum cable length of 3000 feet [914 meters].
V.24 is also listed in the pin-out table, many interfaces use RS422 and RS423 electrical standards.
V.24 was rated at 20 kbps with a maximum range of about 15 meters.

The pinout for the 37-pin connector is listed below.
The pin out for the 9-pin connector is listed on the main EIA-449 Bus page.

RS449 Bus Connector Pin Out
Pin name V.24 Description Type
1   101 Shield Ground
2 SI 112 Signal Rate Indicator Control
3 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   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

V.35/RS449 Max length
Data Rate Cable Length
2 Mb/sec 15.24 Meters
1 Mb/sec 30.48 Meters
512 Kb/sec 60.96 Meters
256 Kb/sec 121.92 Meters
128 Kb/sec 243.84 Meters
56 K 487.68 Meters
1.2 Kb/sec 914.40 Meters

EIA449 Pin Designations and Descriptions
name Description Function
AA Shield Ground Protective ground. Chassis ground connection between DTE and DCE.
AB Signal Ground Ground
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 ----
CC DCE Ready DSR. Originated by the DCE indicating that it is operating
CD DTE Ready DTR. Originated by the DTE to instruct the DCE to setup a connection
CE Ring Indicator Signal from the DCE to the DTE that there is an in-comming call
CF Received Line Signal Detector 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. Instructs the DCE to rapidly get ready to receive a new analog signal
RC Receive Common A signal return for receiver circuit reference
LL Local Loopback / Quality Detector Control signal from the DTE to DCE that causes the analog transmission 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
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.

RS449 is the old term for EIA449. The term RS [Recommended Standard] was replaced in the 70's by the term EIA.
However as of 2011 the EIA group disbanded, which would make this the TIA449 interface.

Back to the main EIA-449 Bus page for a description and pinout of a 9-Pin D connector.

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Modified 6/13/15
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