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

An explanation of the standard, its characteristics including pinouts and how the interface is 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 Name DB37 Contact Supported on FarSync cards
Shield 1 Yes
Signal Rate Indicator 2
Unassigned 3
Send Data (A) 4 Yes
Send Timing (A) 5 Yes
Receive Data (A) 6 Yes
Request To Send (A) 7 Yes
Receive Timing (A) 8 Yes
Clear To Send (A) 9 Yes
Local Loopback 10
Data Mode (A) 11
Terminal Ready (A) 12
Receiver Ready (A) 13
Remote Loopback 14
Incoming Call 15
Select Frequency 16
Terminal Timing (A) 17
Test Mode 18
Signal Ground 19 Yes
Receive Common 20
Unassigned 21
Send Data (B) 22 Yes
Send Timing (B) 23 Yes
Receive Data (B) 24 Yes
Request To Send (B) 25 Yes
Receive Timing (B) 26 Yes
Clear To Send (B) 27 Yes
Terminal In Service 28
Data Mode (B) 29
Terminal Ready (B) 30
Receiver Ready (B) 31
Select Standby 32
Signal Quality 33
New Signal 34
Terminal Timing (B) 35
Standby Indicator 36
Send Common 37

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.