RS-422
RS-422 | |
---|---|
Standard | TIA/EIA-422 |
Physical media | Twisted pair |
Network topology | Point-to-point, multi-dropped |
Maximum devices | 10 (1 driver and 10 receivers) |
Maximum distance | 1,200 meters (3,900 ft) |
Mode of operation | Differential |
Maximum binary rate | 100 kbit/s – 10 Mbit/s |
Voltage levels | −6 to +6 V (maximum voltage for each line) |
Mark (1) | Negative difference |
Space (0) | Positive difference |
Available signals | Tx+, Tx−, Rx+, Rx− (full duplex) |
Connector types | Not specified |
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bb/RS-422_Network.svg/368px-RS-422_Network.svg.png)
RS-422, also known as TIA/EIA-422, is a technical standard originated by the
RS-422 specifies
Standard scope
RS-422 is the common short form title of
The first version of RS-422 was issued in 1975,[4] with revision A issued in December 1978. Revision B, published in May 1994 was reaffirmed by the Telecommunications Industry Association in 2005.
Characteristics
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bd/RS-422_CableLength-DataRate.svg/220px-RS-422_CableLength-DataRate.svg.png)
Several key advantages offered by this standard include the differential receiver, a differential driver and data rates as high as 10 megabits per second at 12 meters (40 ft). Since the signal quality degrades with cable length, the maximum data rate decreases as cable length increases. Figure A.1 in the annex plotting this stops at 10
The maximum cable length is not specified in the standard, but guidance is given in its annex. (This annex is not a formal part of the standard, but is included for information purposes only.) Limitations on line length and data rate vary with the parameters of the cable length, balance, and termination, as well as the individual installation. Figure A.1 shows a maximum length of 1,200 meters (3,900 ft), but this is with a termination, and the annex discusses the fact that many applications can tolerate greater timing and amplitude distortion, and that experience has shown that the cable length may be extended to several kilometers. Conservative maximum data rates with 24
) cable are 10 Mbit/s at 12 m (39 ft) to 90 kbit/s at 1,200 m (3,900 ft), as shown in the figure A.1. This figure is a conservative guide based on empirical data, not a limit imposed by the standard.RS-422 specifies the electrical characteristics of a single balanced signal. The standard was written to be referenced by other standards that specify the complete DTE/DCE interface for applications which require a balanced voltage circuit to transmit data. These other standards would define protocols, connectors, pin assignments and functions. Standards such as
RS-422 cannot implement a true multi-point communications network, such as with EIA-485, since there can be only one driver on each pair of wires. However, one driver can fan-out to up to ten receivers.
RS-422 can interoperate with interfaces designed to MIL-STD-188-114B, but they are not identical. RS-422 uses a nominal 0 to 5-volt signal, while MIL-STD-188-114B uses a signal symmetric about 0 V. However, the tolerance for common-mode voltage in both specifications allows them to interoperate. Care must be taken with the termination network.
When used in relation to communications wiring, RS-422 wiring refers to cable made of 2 sets of twisted pair, often with each pair being shielded, and a ground wire. While a double-pair cable may be practical for many RS-422 applications, the RS-422 specification only defines one signal path and does not assign any function to it. Any complete cable assembly with connectors should be labeled with the specification that defined the signal function and mechanical layout of the connector, such as RS-449.
Applications
One of the most widespread uses of RS-422 was on the early
RS-422 is a common transport mechanism for RS-232 extenders. These consist of RS-232 ports on either end of an RS-422 connection.
Before hard-disk-based playout and editing systems were used,
which is still found on broadcast equipment today.See also
References
- ^ "EIA-423". foldoc.org. Retrieved 8 July 2021.
- ^ "V.11 : Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s". International Telecommunication Union. Retrieved 19 September 2022.
- ^ TIA/EIA STANDARD, Electrical Characteristics of Balanced Voltage Digital Interface Circuits, TIA/EIA-422-B, May 1994
- ISBN 0835943658page 569
- ^ "First Macintosh Press Release". stanford.edu. 1984. Retrieved 8 July 2021.
- ^ Sony 9-Pin Remote Protocol.
Further reading
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Wikibooks-logo-en-noslogan.svg/40px-Wikibooks-logo-en-noslogan.svg.png)
- "Maxim IC Application Note 723 'Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards'" (PDF). MaximIntegrated.com. Maxim Integrated Products. December 2000.
- "Texas Instruments Application Report '422 and 485 Standards Overview and System Configurations'" (PDF). Focus.TI.com. Texas Instruments. June 2002.
- "Texas Instruments Application Report SLLA067B 'Comparing Bus Solutions'" (PDF). Focus.TI.com. Texas Instruments. October 2009.