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.
| 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.