Editing Baudot code (section)

==={{anchor|MTK-2}}ITA2===
{{Infobox character encoding
| name = ITA2 Baudot–Murray code
| alias = International Telegraph Alphabet 2
| image = International Telegraph Alphabet 2 brightened.jpg
| caption = British variant of ITA2
| prev = [[#ITA1|ITA1]]
| next = [[FIELDATA]],<br />[[ARQ-M#ITA3|ITA 3 (van Duuren code)]],<br />[[ITU T.50|ITA 5]] ([[ISO 646]], [[ASCII]])
| classification = 5-bit [[state (computer science)|stateful]]{{citation needed|date=October 2023}} [[ISO Basic Latin alphabet|basic Latin]] encoding
}}
{{Infobox character encoding
| name = MTK-2
| alias = 
| image = 
| caption = 
| prev = [[Russian Morse code]]
| next = [[KOI-7]]
| lang = [[Russian language|Russian]]
| classification = 5-bit [[state (computer science)|stateful]]{{citation needed|date=October 2023}} [[Russian alphabet|Russian Cyrillic]] encoding
}}
In 1932, the [[CCITT]] introduced the '''International Telegraph Alphabet No. 2''' ('''ITA2''') code<ref>{{cite web |url=http://handle.itu.int/11.1004/020.1000/4.5.43.en.101 |title=Telegraph Regulations and Final Protocol (Madrid, 1932) |access-date=10 May 2024 |archive-url=https://web.archive.org/web/20230821020920/https://search.itu.int/history/HistoryDigitalCollectionDocLibrary/4.5.43.en.101.pdf |archive-date=21 August 2023}}</ref> as an international standard, which was based on the Western Union code with some minor changes. The US standardized on a version of ITA2 called the [[American Teletypewriter code]] (US TTY) which was the basis for 5-bit teletypewriter codes until the debut of 7-bit [[ASCII]] in 1963.<ref>{{cite web | last = Smith | first = Gil | title = Teletype Communication Codes | publisher = Baudot.net | year = 2001 | url = http://www.baudot.net/docs/smith--teletype-codes.pdf | access-date = 2008-07-11| archive-url= https://web.archive.org/web/20080820043949/http://www.baudot.net/docs/smith--teletype-codes.pdf| archive-date= 20 August 2008 <!--DASHBot-->|url-status = live}}</ref>

Some code points (marked blue in the table) were reserved for national-specific usage.<ref name="Steinbuch-Weber_1974">{{cite book |title=Taschenbuch der Informatik - Band III - Anwendungen und spezielle Systeme der Nachrichtenverarbeitung |language=de |editor-first1=Karl W. |editor-last1=Steinbuch |editor-link1=Karl W. Steinbuch |editor-first2=Wolfgang |editor-last2=Weber |date=1974 |orig-year=1967 |edition=3 |volume=3 |work=Taschenbuch der Nachrichtenverarbeitung |publisher=[[Springer Verlag]] |location=Berlin, Germany |isbn=3-540-06242-4 |lccn=73-80607 |pages=328–329}}</ref>

[[File:Cyrillic teletype keyboard.jpg|thumb|A four-row teletype keyboard with Roman and Cyrillic letters.]]
{|class="wikitable sortable collapsible" style="border:none"
|+International telegraphy alphabet No. 2 (Baudot–Murray code)<ref>{{Cite web | last = dataIP Limited | title = The "Baudot" Code | url = http://www.dataip.co.uk/technical-information/the-baudot-code/ | access-date = 16 July 2017 | archive-url = https://web.archive.org/web/20171223093021/http://www.dataip.co.uk/technical-information/the-baudot-code/ | archive-date = 23 December 2017}}</ref>
|-
!scope="col" colspan="3"| Impulse patterns<br/> (1=mark, 0=space)
!scope="col" colspan="2"| Letter shift
!scope="col" colspan="3"| Figure shift
|-
!scope="col" width="6em"| [[Least significant bit|LSB]] on<br /> right;<br />''code elements:''<br /> 543·21
!scope="col" width="6em"| [[Least significant bit|LSB]] on<br /> left;<br /> ''code elements:''<br /> 12·345
!scope="col" width="2em"| Count of punched marks
!scope="col" width="4em"| ITA2<br /> standard
!scope="col" width="4em"| Russian<br />MTK-2<br /> variant
!scope="col" width="4em"| Russian<br />MTK-2<br /> variant
!scope="col" width="4em"| ITA2<br /> standard
!scope="col" width="4em"| US TTY<br /> variant
|-
| 000·00 || 00·000 || 0 ||colspan="2" style="background:#CCF"| Null || style="background:#FCC" | Shift to Russian Letters (RS) ||colspan="2" style="background:#CCF"| Null 
|-		        
| 010·00 || 00·010 || 1 ||style="background:#FCC" colspan="5"| Carriage return
|-		        
| 000·10 || 01·000 || 1 ||style="background:#FCC" colspan="5"| Line feed
|-		        
| 001·00 || 00·100 || 1 ||colspan="5"| Space
|-		        
| 101·11 || 11·101 || 4 || Q || Я ||colspan="3"| 1
|-		        
| 100·11 || 11·001 || 3 || W || В ||colspan="3"| 2
|-		        
| 000·01 || 10·000 || 1 || E || Е ||colspan="3"| 3
|-		        
| 010·10 || 01·010 || 2 || R || Р || 4, Ч ||colspan="2"| 4
|-		        
| 100·00 || 00·001 || 1 || T || Т ||colspan="3"| 5
|-		        
| 101·01 || 10·101 || 3 || Y || Ы ||colspan="3"| 6
|-		        
| 001·11 || 11·100 || 3 || U || У ||colspan="3"| 7
|-		        
| 001·10 || 01·100 || 2 || I || И ||colspan="3"| 8
|-		        
| 110·00 || 00·011 || 2 || O || О ||colspan="3"| 9
|-		        
| 101·10 || 01·101 || 3 || P || П ||colspan="3"| 0
|-		        
| 000·11 || 11·000 || 2 || A || А ||colspan="3"| –
|-		        
| 001·01 || 10·100 || 2 || S || С ||colspan="2"| ' ||style="background:#FCC"| Bell
|-		        
| 010·01 || 10·010 || 2 || D || Д ||colspan="2"| <abbr title="Who are you?">WRU?</abbr> || $
|-		        
| 011·01 || 10·110 || 3 || F || Ф || style="background:#CCF"|Э || style="background:#CCF" colspan="2"| !
|-		        
| 110·10 || 01·011 || 3 || G || Г || style="background:#CCF"|Ш || style="background:#CCF" colspan="2"| &
|-		        
| 101·00 || 00·101 || 2 || H || Х || style="background:#CCF"|Щ || style="background:#CCF"|£ || style="background:#CCF"|#
|-		        
| 010·11 || 11·010 || 3 || J || Й || Ю, Bell ||style="background:#FCC"| Bell || '
|-		        
| 011·11 || 11·110 || 4 || K || К ||colspan="3"| (
|-		        
| 100·10 || 01·001 || 2 || L || Л ||colspan="3"| )
|-		        
| 100·01 || 10·001 || 2 || Z || З ||colspan="2"| + || "
|-		        
| 111·01 || 10·111 || 4 || X || Ь ||colspan="3"| /
|-		        
| 011·10 || 01·110 || 3 || C || Ц ||colspan="3"| :
|-		        
| 111·10 || 01·111 || 4 || V || Ж ||colspan="2"| = || ;
|-		        
| 110·01 || 10·011 || 3 || B || Б ||colspan="3"| ?
|-		        
| 011·00 || 00·110 || 2 || N || Н ||colspan="3"| ,
|-		        
| 111·00 || 00·111 || 3 || M || М ||colspan="3"| .
|-		        
| 110·11 || 11·011 || 4 ||style="background:#FCC" colspan="2"| Shift to Figures (FS) ||style="background:#CCC" colspan="3"| ''Reserved for<br/> figures extension''
|-		        
| 111·11 || 11·111 || 5 ||style="background:#CCC" colspan="2"| ''Reserved for<br/> lettercase extension'' ||style="background:#FCC" colspan="3"| Shift to Letters (LS)<br /> / Erasure / Delete
|}

The code position assigned to Null was in fact used only for the idle state of teleprinters. During long periods of idle time, the impulse rate was not synchronized between both devices (which could even be powered off or not permanently interconnected on commuted phone lines). To start a message it was first necessary to calibrate the impulse rate, a sequence of regularly timed "mark" pulses (1), by a group of five pulses, which could also be detected by simple passive electronic devices to turn on the teleprinter. This sequence of pulses generated a series of Erasure/Delete characters while also initializing the state of the receiver to the Letters shift mode. However, the first pulse could be lost, so this power on procedure could then be terminated by a single Null immediately followed by an Erasure/Delete character. To preserve the synchronization between devices, the Null code could not be used arbitrarily in the middle of messages (this was an improvement to the initial Baudot system where spaces were not explicitly differentiated, so it was difficult to maintain the pulse counters for repeating spaces on teleprinters). But it was then possible to resynchronize devices at any time by sending a Null in the middle of a message (immediately followed by an Erasure/Delete/LS control if followed by a letter, or by a FS control if followed by a figure). Sending Null controls also did not cause the paper band to advance to the next row (as nothing was punched), so this saved precious lengths of punchable paper band. On the other hand, the Erasure/Delete/LS control code was always punched and always shifted to the (initial) letters mode. According to some sources, the Null code point was reserved for country-internal usage only.<ref name="Steinbuch-Weber_1974"/>

The Shift to Letters code (LS) is also usable as a way to cancel/delete text from a punched tape after it has been read, allowing the safe destruction of a message before discarding the punched band.{{clarify|date=October 2020}} Functionally, it can also play the same filler role as the Delete code in ASCII (or other 7-bit and 8-bit encodings, including EBCDIC for punched cards). After codes in a fragment of text have been replaced by an arbitrary number of LS codes, what follows is still preserved and decodable. It can also be used as an initiator to make sure that the decoding of the first code will not give a digit or another symbol from the figures page (because the Null code can be arbitrarily inserted near the end or beginning of a punch band, and has to be ignored, whereas the Space code is significant in text).

The cells marked as reserved for extensions (which use the LS code again a second time—just after the first LS code—to shift from the figures page to the letters shift page) has been defined to shift into a new mode. In this new mode, the letters page contains only lowercase letters, but retains access to a third code page for uppercase letters, either by encoding for a single letter (by sending LS before that letter), or locking (with FS+LS) for an unlimited number of capital letters or digits before then unlocking (with a single LS) to return to lowercase mode.<ref>[[ITU-T]] [https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-S.1-198811-S!!PDF-E Recommendation S.2 / 11/1988], published in Fascicle VII.1 of the ''Blue Book''</ref> The cell marked as "Reserved" is also usable (using the FS code from the figures shift page) to switch the page of figures (which normally contains digits and ''national'' lowercase letters or symbols) to a fourth page (where national letters are uppercase and other symbols may be encoded).

ITA2 is still used in [[telecommunications devices for the deaf]] (TDD), [[Telex]], and some [[amateur radio]] applications, such as [[radioteletype]] ("RTTY"). ITA2 is also used in Enhanced Broadcast Solution, an early 21st-century financial protocol specified by [[Deutsche Börse]], to reduce the character encoding footprint.<ref>{{Cite web | title = Enhanced Broadcast Solution – Interface Specification Final Version | publisher = Deutsche Börse | date = 17 May 2010 | url = https://www9.deutsche-boerse.com/INTERNET/XETRA/x4_member.nsf/0/4502210270B32DA8C1257600005247F5/$FILE/MUI11010_EnBS_FinalVersion.pdf/MUI11010_EnBS_FinalVersion.pdf?OpenElement | access-date = 10 August 2011 | archive-date = 8 February 2012 | archive-url = https://web.archive.org/web/20120208070449/https://www9.deutsche-boerse.com/INTERNET/XETRA/x4_member.nsf/0/4502210270B32DA8C1257600005247F5/$FILE/MUI11010_EnBS_FinalVersion.pdf/MUI11010_EnBS_FinalVersion.pdf?OpenElement | url-status = dead }}</ref>