View source for RS-423

{{Short description|Standard for serial communication}}
{{Infobox fieldbus protocol
|name              = RS423
| standard = EIA RS-423
|governing_body    =
|website           =
|type_of_network   =
|physical_media    = Group of copper cables
|network_topology  = Point-to-point, Multi-dropped
|maximum_devices   = 10 (1 driver & 10 receivers)
|maximum_distance  = 1200 meters (4000&nbsp;feet)
|maximum_speed     =
|device_addressing =
|mode_of_operation = Single-ended (unbalanced)
|maximum_baud_rate =Up to 100kbit/s
|voltage = -6V to +6V (maximum)
|mark1=-4V to -6V
|space0=+4V to +6V
|available_signals=Tx, Rx, GND
|connector_types = Not specified
}}

'''RS-423''', also known as '''TIA/EIA-423''', is a technical standard originated by the [[Electronic Industries Alliance]] that specifies electrical characteristics of a digital signaling circuit. Although it was originally intended as a successor to [[RS-232C]] offering greater cable lengths, it is not widely used.

RS-423 systems can transmit data on cables as long as {{Convert|1200|m|sp=us}}.{{dubious|Maximum length|date=September 2021}} It is closely related to [[RS-422]], which used the same signaling systems but on a different wiring arrangement: RS-423 differed primarily in that it had a single return pin instead of one for each data pin.<ref>{{cite web |title=EIA-423 |url=http://foldoc.org/rs-423|publisher=foldoc.org|access-date=2021-07-08}}</ref>

RS-423 specifies an [[unbalanced circuit|unbalanced]] ([[Single-ended signaling|single-ended]]) interface, similar to [[RS-232]], with a single, unidirectional sending driver, and allowing for up to 10 receivers.<ref>Buchanan W.J. (2004) RS-422, RS-423 and RS-485. In: ''The Handbook of Data Communications and Networks.'' Springer, Boston, MA.{{ISBN|978-1-4757-1067-0}} page 627</ref> It is normally implemented in integrated circuit technology and can also be employed for the interchange of serial binary signals between [[Data terminal equipment|DTE]] & [[Data circuit-terminating equipment|DCE]].

==Standard scope==
RS-423 is the common short form title of [[American National Standards Institute]] (ANSI) standard ''ANSI/TIA/EIA-423-B Electrical Characteristics of Unbalanced Voltage Digital Interface Circuits'' and its international equivalent ''ITU-T Recommendation T-REC-V.10'',<ref>{{cite web |title=V.10 : Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to 100&nbsp;kbit/s |url=https://www.itu.int/rec/T-REC-V.10/en%20V.10%20ITU%20Recommendation%20T-REC-V.10|website=itu.int |access-date=3 May 2023}}</ref> also known as ''X.26''. These technical [[Standardization|standard]]s specify the electrical characteristics of the unbalanced voltage digital interface circuit.<ref name="definition">''TIA/EIA STANDARD, Electrical Characteristics of Unbalanced Voltage Digital Interface Circuits, TIA/EIA-423-B'', May 1993</ref> RS-423 provides for data transmission, using [[unbalanced circuit|unbalanced]] or [[Single-ended signaling|single-ended]] signals, with unidirectional/non-reversible, [[Electrical termination|terminated]] or non-terminated transmission lines, point to point, or multi-drop.

== Characteristics ==
[[File:RS signal rate.svg|thumb|Guidelines for data rate versus line length]]
RS-423 is closely related to the [[RS-422]] standard, both of which use the same overall signaling system, but differ in that RS-422 has a dedicated return line for every data pin, while RS-423 uses a single return line. Use of a common ground is one weakness of RS-423 (and [[RS-232]]): if devices are far enough apart or on separate power systems, the ground will degrade between them and communications will fail, resulting in a condition that is difficult to trace.<ref>[http://www.ti.com/lit/an/snla044b/snla044b.pdf National Semiconductor Application Note AN-1031 "TIA/EIA-422-B Overview", January 2000, National Semiconductor Inc.] page 2 - evaluate the combination of cable length and data rate.</ref>

RS-423 specifies the electrical characteristics of a single unbalanced signal. The standard was written to be referenced by other standards that specify the complete DTE/DCE interface for applications which require a unbalanced voltage circuit to transmit data.{{citation needed|date=May 2023}}

These other standards would define protocols, connectors, pin assignments and functions. Standards such as [[EIA-530]] ([[DB-25]] connector) and [[EIA-449]] ([[D-subminiature|DC-37]] connector) use RS-423 electrical signals.{{citation needed|date=May 2023}}

== Applications ==
The [[BBC Micro]] computer uses RS-423 with a 5-pin [[DIN connector]]. [[Digital Equipment Corporation|DEC]] used it extensively with a [[Modified Modular Jack]] connector. This was sometimes called "DEC-423".{{citation needed|date=May 2023}}

==See also==
* [[Electronic Industries Alliance]]
* [[RS-485]]
* [[Profibus]]
* [[Fieldbus]]
* [[List of network buses]]

==References==
{{Reflist}}

==Further reading==
{{Wikibooks|Serial Programming/RS-423}}
* [http://pinouts.ru/SerialPorts/rs-423_pinout.shtml RS-423 specification]
* [http://www.zprod.org/PG/machines/bbcMicroInterface.htm Diagram of pin connections for BBC micro]

{{Computer-bus}}

{{DEFAULTSORT:Rs-423}}
[[Category:Serial buses]]
[[Category:EIA standards]]