EIA-422
Encyclopedia
| RS422 | |
|---|---|
| Standard | EIA RS-422 |
| Physical Media | Twisted Pair |
| Network Topology | Point-to-point, Multi-dropped |
| Maximum Devices | 10 (1 driver & 10 receivers) |
| Maximum Distance | 1200 metres (4000 ft) |
| Mode of Operation | Differential |
| Maximum Baud Rate | 100 kbit/s - 10 Mbit/s |
| Voltage Levels | -6V to +6V (maximum differential Voltage) |
| Mark(1) | Negative Voltages |
| Space(0) | Positive voltages |
| Available Signals | Tx+, Tx-, Rx+, Rx- (Full Duplex) |
| Connector types | Not specified |
RS-422 is a technical standard that specifies electrical characteristics of a digital signalling circuit. Differential-mode signals can be sent at rates as high as 10 million bits per second, or may be sent on cables as long as 1200 metres. Some systems directly interconnect using RS 422 signals, or RS 422 converters may be used to extend the range of RS 232 connections. The standard only defines signal levels; other properties of a serial interface are set by other standards.
Standard scope
RS 422 is the common short form title of American National Standards InstituteAmerican National Standards Institute
The American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
(ANSI) standard ANSI/TIA/EIA-422-B Electrical Characteristics of Balanced Voltage Differential Interface Circuits and its international equivalent
ITU-T Recommendation T-REC-V.11, also known as X.27. These technical standard
Standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....
s specify the electrical characteristics of the balanced voltage digital interface circuit. RS-422 provides for data transmission, using balanced or differential signaling
Differential signaling
Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...
, with unidirectional/non-reversible, terminated
Electrical termination
Electrical termination of a signal involves providing a terminator at the end of a wire or cable to prevent an RF signal from being reflected back from the end, causing interference...
or non-terminated transmission lines, point to point, or multi-drop. In contrast to EIA-485 (which is multi-point instead of multi-drop), EIA-422/V.11 does not allow multiple drivers but only multiple receivers.
Revision B, published in May 1994 was reaffirmed by the Telecommunications Industry Association
Telecommunications Industry Association
The Telecommunications Industry Association is accredited by the American National Standards Institute to develop voluntary, consensus-based industry standards for a wide variety of ICT products, and currently represents nearly 400 companies...
in 2005.
Characteristics
Several key advantages offered by this standard include the differential receiver, a differential driver and data rates as high as 10 megabaudBaud
In telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
at 12 metres (40 ft). The specification itself does not set an upper limit on data rate, but rather shows how signal rate degrades with cable length. The figure plotting this stops at 10 Mbit/s
Bitrate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
.
EIA-422 only specifies the electrical signaling characteristics of a single balanced signal. Protocols and pin assignments are defined in other specifications. The mechanical connections for this interface are specified by EIA-530
EIA-530
Currently known asTIA-530-A, but often called EIA-530, or RS-530, is a balanced serial interface standard that generally uses a 25-pin connector, originally created by the Telecommunications Industry Association....
(DB-25 connector) or EIA-449 (DC-37
D-subminiature
The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smaller connectors used on computer systems....
connector), however devices exist which have 4 screw-posts to implement the transmit and receive pair only. The maximum cable length is 1200 m. Maximum data rates are 10 Mbit/s at 12 m or 100 kbit/s at 1200 m. EIA-422 cannot implement a truly multi-point communications network such as with EIA-485, however one driver can be connected to up to ten receivers.
A common use of EIA-422 is for RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
extenders.
Broadcast automation
Broadcast automation
Broadcast automation incorporates the use of broadcast programming technology to automate broadcasting operations. Used either at a broadcast network, radio station or a television station, it can run a facility in the absence of a human operator...
systems and post-production
Post-production
Post-production is part of filmmaking and the video production process. It occurs in the making of motion pictures, television programs, radio programs, advertising, audio recordings, photography, and digital art...
linear editing facilities use RS-422A to remotely control the players/recorders located in the central apparatus room
Central Apparatus Room
In broadcast facilities, a central apparatus room , central machine room, or central equipment room , or central technical area , or rack room is where shared equipment common to all technical areas is located. Some broadcast facilities have several of these rooms...
.
Also, an RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
-compatible variant of RS-422 using a mini-DIN
Mini-DIN connector
The mini-DIN connectors are a family of multi-pin electrical connectors used in a variety of applications. Mini-DIN is similar to the larger, older DIN connector...
-8 connector was widely used on Macintosh hardware until it was replaced by Universal Serial Bus
Universal Serial Bus
USB is an industry standard developed in the mid-1990s that defines the cables, connectors and protocols used in a bus for connection, communication and power supply between computers and electronic devices....
on the iMac
IMac
The iMac is a range of all-in-one Macintosh desktop computers built by Apple. It has been the primary part of Apple's consumer desktop offerings since its introduction in 1998, and has evolved through five distinct forms....
in 1998.
EIA-422 can interoperate with interfaces designed to MIL-STD-188-114B
MIL-STD-188
MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...
, but they are not identical. EIA-422 uses a nominal 0 to 5 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
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.
EIA-423 is a similar specification for unbalanced signaling (RS-423
RS-423
RS/EIA/TIA-423 is a standard for serial communications. It defines an unbalanced interface , with a single, unidirectional sending driver, and allows for up to 10 receivers . It is normally implemented in integrated circuit technology and can also be employed for the interchange of serial binary...
).
When used in relation to communications wiring, RS-422 wiring refers to cable made of 2 sets of twisted pair
Twisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
, 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 (i.e. with connectors) should be labeled with the specification that defined the signal function and mechanical layout of the connector, such as RS-449
RS-449
The RS-449 specification, also known as EIA-449 or TIA-449, defines the functional and mechanical characteristics of the interface between data terminal equipment and data communications equipment....
.
See also
- Electronic Industries AllianceElectronic Industries AllianceThe Electronic Industries Alliance was a standards and trade organization composed as an alliance of trade associations for electronics manufacturers in the United States. They developed standards to ensure the equipment of different manufacturers was compatible and interchangeable...
- ProfibusProfibusPROFIBUS is a standard for field bus communication in automation technology and was first promoted in 1989 by BMBF...
- FieldbusFieldbusFieldbus is the name of a family of industrial computer network protocols used for real-time distributed control, now standardized as IEC 61158....
- List of network buses
External links
- The Telecommunications Industry Association
- National Semiconductor Application Note AN-1031 "TIA/EIA-422-B Overview", January 2000, National Semiconductor Inc., retrieved from http://www.national.com/an/AN/AN-1031.pdf
- National Semiconductor Application Note AN-759 "Comparing EIA-485 and EIA-422-A Line Drivers and Receivers in Multipoint Applications", February 1991, National Semiconductor Inc., retrieved from http://www.national.com/an/AN/AN-759.pdf
- National Semiconductor Application Note AN-214 "Transmission Line Drivers and Receivers or TIA/EIA Standards RS-422 and RS-423" August 1993, National Semiconductor Inc., retrieved from http://www.national.com/an/AN/AN-214.pdf
- Maxim IC Application Note 723 "Selecting and Using RS-232, RS-422, and RS-485 Serial Data Standards" Dec 2000,
Maxim Integrated Products, Inc., retrieved from http://www.maxim-ic.com/appnotes.cfm/appnote_number/723
- Texas Instruments Application Report "422 and 485 Standards Overview and System Configurations" June 2002, Texas Instruments, retrieved from http://focus.ti.com/lit/an/slla070d/slla070d.pdf
- Texas Instruments Application Report SLLA067B "Comparing Bus Solutions" October 2009, Texas Instruments, retrieved from http://focus.ti.com/lit/an/slla067b/slla067b.pdf