RS-449, EIA-449 (RS449, EIA449) Connector / Signaling Standard

An explanation of the standards, their characteristics including pinouts and how the interfaces are generally used in practice.

Interface Standards

RS-449 ( often written as RS449 ) is a specification for a differential communications interface that uses a DB-37 connector and differential equivalents of the V.24 (RS-232) signals. Some of the link management control signals are implemented using V.10 (RS-423) single ended interfaces. Note that the EIA standards have effectively replaced the RS standards. Note also that RS-449 and EIA-449 (often written as EIA449) are also sometimes referred to as V.36 (a modem standard that specifies an RS-449 type data interface).

Interface Characteristics

RS-449 is a differential communications interface used for synchronous communications with some single-ended link management signals, typically limited to a maximum throughput of 10Mbps. Communications over distances exceeding 1000m is possible at low bit rates, the actual performance being mostly dependent on cable specification. Separate clock lines are used for receiving and transmitting data.

Interface Applications

RS-449 interfaces are commonly found on communications equipment in some parts of the world where high throughput and/or long distances are required. The interface also offers good noise immunity enabling reliable communications in environments where there are high levels of EMI (electromagnetic interference).

Interface Connector Types and Pinouts

The signals used by the overwhelming majority of applications are marked in bold.


DB37 Connector Pinouts
Signal NameDB37 ContactSupported on FarSync cards
Signal Rate Indicator2
Send Data (A)4Yes
Send Timing (A)5Yes
Receive Data (A)6Yes
Request To Send (A)7Yes
Receive Timing (A)8Yes
Clear To Send (A)9Yes
Local Loopback10
Data Mode (A)11
Terminal Ready (A)12
Receiver Ready (A)13
Remote Loopback14
Incoming Call15
Select Frequency16
Terminal Timing (A)17
Test Mode18
Signal Ground19Yes
Receive Common20
Send Data (B)22Yes
Send Timing (B)23Yes
Receive Data (B)24Yes
Request To Send (B)25Yes
Receive Timing (B)26Yes
Clear To Send (B)27Yes
Terminal In Service28
Data Mode (B)29
Terminal Ready (B)30
Receiver Ready (B)31
Select Standby32
Signal Quality33
New Signal34
Terminal Timing (B)35
Standby Indicator36
Send Common37

The RS449, EIA449 standard is supported on the FarSync range of communications products

Note: FarSite specifies the use of one of two conversion cables (for use with either a DCE-supplied Clock or a DTE-supplied clock) for use with a FarSync product and a matching X.21 cable.