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Baudot code

January 07, 2023

The Baudot code [boˈdo] is an early character encoding for telegraphy invented by Émile Baudot in the 1870s.[1] It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the most common teleprinter code in use until the advent of ASCII. Each character in the alphabet is represented by a series of five bits, sent over a communication channel such as a telegraph wire or a radio signal by asynchronous serial communication. The symbol rate measurement is known as baud, and is derived from the same name.

An early "piano" Baudot keyboard

History

Baudot code (ITA1)

Baudot code (ITA1)
 
An early version from Baudot's 1888 US patent, listing A through Z, t and ∗ (Erasure)
Alias(es)International Telegraph Alphabet 1
Current statusReplaced by ITA2 (not mutually compatible).
Classification5-bit stateful basic Latin encoding
Preceded byMorse code
Succeeded byITA2

In the below table, Columns I, II, III, IV, and V show the code; the Let. and Fig. columns show the letters and numbers for the Continental and UK versions; and the sort keys present the table in the order: alphabetical, Gray and UK

Baudot code (Continental and UK versions)
Europe sort keys UK sort keys
V IV I II III Con­ti­nen­tal Gray Let. Fig. V IV I II III UK
- - -
A 1 ● A 1 ●
É & ● ● / 1/ ● ●
E 2 ● E 2 ●
I o ● ● I 3/ ● ●
O 5 ● ● ● O 5 ● ● ●
U 4 ● ● U 4 ● ●
Y 3 ● Y 3 ●
● B 8 ● B 8 ● ●
● C 9 ● ● C 9 ● ● ●
● D 0 ● ● ● D 0 ● ● ● ●
● F f ● ● F 5/ ● ● ●
● G 7 ● G 7 ● ●
● H h ● ● H ¹ ● ● ●
● J 6 ● J 6 ● ●
● Figure Blank Fig. Bl. ●
● ● Erasure Erasure * * ● ●
● ● K ( ● K ( ● ● ●
● ● L = ● ● L = ● ● ● ●
● ● M ) ● M ) ● ● ●
● ● N N° ● ● N £ ● ● ● ●
● ● P % ● ● ● P + ● ● ● ● ●
● ● Q / ● ● Q / ● ● ● ●
● ● R – ● R – ● ● ●
● S ; ● S 7/ ● ●
● T ! ● ● T ² ● ● ●
● V ' ● ● ● V ¹ ● ● ● ●
● W ? ● ● W ? ● ● ●
● X , ● X 9/ ● ●
● Z : ● ● Z : ● ● ●
● t . ● – . ● ●
● Blank Letter Bl. Let. ●

Baudot developed his first multiplexed telegraph in 1872[2][3] and patented it in 1874.[3][4] In 1876, he changed from a six-bit code to a five-bit code,[3] as suggested by Carl Friedrich Gauss and Wilhelm Weber in 1834,[2][5] with equal on and off intervals, which allowed for transmission of the Roman alphabet, and included punctuation and control signals. The code itself was not patented (only the machine) because French patent law does not allow concepts to be patented.[6]

Baudot's 5-bit code was adapted to be sent from a manual keyboard, and no teleprinter equipment was ever constructed that used it in its original form.[7] The code was entered on a keyboard which had just five piano-type keys and was operated using two fingers of the left hand and three fingers of the right hand. Once the keys had been pressed, they were locked down until mechanical contacts in a distributor unit passed over the sector connected to that particular keyboard, at which time the keyboard was unlocked ready for the next character to be entered, with an audible click (known as the "cadence signal") to warn the operator. Operators had to maintain a steady rhythm, and the usual speed of operation was 30 words per minute.[8]

The table "shows the allocation of the Baudot code which was employed in the British Post Office for continental and inland services. A number of characters in the continental code are replaced by fractionals in the inland code. Code elements 1, 2 and 3 are transmitted by keys 1, 2 and 3, and these are operated by the first three fingers of the right hand. Code elements 4 and 5 are transmitted by keys 4 and 5, and these are operated by the first two fingers of the left hand."[7][9][10]

Baudot's code became known as the International Telegraph Alphabet No. 1 (ITA1). It is no longer used.

Murray code

 
Paper tape with holes representing the "Baudot–Murray Code". Note the fully punched columns of "Delete/Letters select" codes at end of the message (on the right) which were used to cut the band easily between distinct messages. The last symbols before the fully punched columns at the end are BRASIL CR LF CR FS (word Brasil, carriage return, line feed, carriage return, shift to figures)

In 1901, Baudot's code was modified by Donald Murray (1865–1945), prompted by his development of a typewriter-like keyboard. The Murray system employed an intermediate step; a keyboard perforator, which allowed an operator to punch a paper tape, and a tape transmitter for sending the message from the punched tape. At the receiving end of the line, a printing mechanism would print on a paper tape, and/or a reperforator could be used to make a perforated copy of the message.[11] As there was no longer a connection between the operator's hand movement and the bits transmitted, there was no concern about arranging the code to minimize operator fatigue, and instead Murray designed the code to minimize wear on the machinery, assigning the code combinations with the fewest punched holes to the most frequently used characters.[12][13]

For example, the one-hole letters are E and T. The ten two-hole letters are AOINSHRDLZ, very similar to the "Etaoin shrdlu" order used in Linotype machines. Ten more letters, BCGFJMPUWY, have three holes each, and the four-hole letters are VXKQ.

The Murray code also introduced what became known as "format effectors" or "control characters" – the CR (Carriage Return) and LF (Line Feed) codes. A few of Baudot's codes moved to the positions where they have stayed ever since: the NULL or BLANK and the DEL code. NULL/BLANK was used as an idle code for when no messages were being sent, but the same code was used to encode the space separation between words. Sequences of DEL codes (fully punched columns) were used at start or end of messages or between them, allowing easy separation of distinct messages. (BELL codes could be inserted in those sequences to signal to the remote operator that a new message was coming or that transmission of a message was terminated).

Early British Creed machines also used the Murray system.

Western Union

 
Keyboard of a teleprinter using the Baudot code (US variant), with FIGS and LTRS shift keys

Murray's code was adopted by Western Union which used it until the 1950s, with a few changes that consisted of omitting some characters and adding more control codes. An explicit SPC (space) character was introduced, in place of the BLANK/NULL, and a new BEL code rang a bell or otherwise produced an audible signal at the receiver. Additionally, the WRU or "Who aRe yoU?" code was introduced, which caused a receiving machine to send an identification stream back to the sender.

ITA2

ITA2 Baudot–Murray code
 
British variant of ITA2
Alias(es)International Telegraph Alphabet 2
Classification5-bit stateful basic Latin encoding
Preceded byITA1
Succeeded byFIELDATA,
ITA 3 (van Duuren code),
ITA 5 (ISO 646, ASCII)
MTK-2
Language(s)Russian
Classification5-bit stateful Russian Cyrillic encoding
Preceded byRussian Morse code
Succeeded byKOI-7

In 1924, the CCITT introduced the International Telegraph Alphabet No. 2 (ITA2) code[14] 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.[15]

Some code points (marked blue in the table) were reserved for national-specific usage.[16]

 
A four-row teletype keyboard with Roman and Cyrillic letters.
International telegraphy alphabet No. 2 (Baudot–Murray code)[17]
Impulse patterns
(1=mark, 0=space) 		Letter shift Figure shift
LSB on
right;
code elements:
543·21 		LSB on
left;
code elements:
12·345 		Count of punched marks ITA2
standard 		Russian
MTK-2
variant 		Russian
MTK-2
variant 		ITA2
standard 		US TTY
variant
000·00 00·000 0 Null Shift to Cyrillic Letters Null
010·00 00·010 1 Carriage return
000·10 01·000 1 Line feed
001·00 00·100 1 Space
101·11 11·101 4 Q Я 1
100·11 11·001 3 W В 2
000·01 10·000 1 E Е 3
010·10 01·010 2 R Р 4
100·00 00·001 1 T Т 5
101·01 10·101 3 Y Ы 6
001·11 11·100 3 U У 7
001·10 01·100 2 I И 8
110·00 00·011 2 O О 9
101·10 01·101 3 P П 0
000·11 11·000 2 A А –
001·01 10·100 2 S С ' Bell
010·01 10·010 2 D Д WRU? $
011·01 10·110 3 F Ф Э !
110·10 01·011 3 G Г Ш &
101·00 00·101 2 H Х Щ £ #
010·11 11·010 3 J Й Ю Bell '
011·11 11·110 4 K К (
100·10 01·001 2 L Л )
100·01 10·001 2 Z З + "
111·01 10·111 4 X Ь /
011·10 01·110 3 C Ц :
111·10 01·111 4 V Ж = ;
110·01 10·011 3 B Б ?
011·00 00·110 2 N Н ,
111·00 00·111 3 M М .
110·11 11·011 4 Shift to Figures (FS) Reserved for
figures extension
111·11 11·111 5 Reserved for
lettercase extension		 Shift to Letters (LS)
/ 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.[16]

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.[clarification needed] 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.[18] 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.[19]

Nomenclature

Nearly all 20th-century teleprinter equipment used Western Union's code, ITA2, or variants thereof. Radio amateurs casually call ITA2 and variants "Baudot" incorrectly,[20] and even the American Radio Relay League's Amateur Radio Handbook does so, though in more recent editions the tables of codes correctly identifies it as ITA2.

Character set

The values shown in each cell are the Unicode codepoints, given for comparison.

Original Baudot variants

Original Baudot, domestic UK

Original Baudot code, UK domestic variant (letter set, switched to with 0x10)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL A E / Y U I O FIGS J G H B C F D
1x  SP  - X Z S T W V DEL K M L R Q N P
Original Baudot code, UK domestic variant (figure set, switched to with 0x08)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL 1 2 ⅟ 3 4 ³⁄ 5  SP  6 7 ¹ 8 9 ⁵⁄ 0
1x LTRS . ⁹⁄ : ⁷⁄ ² ? ' DEL ( ) = - / £ +

Original Baudot, Continental European

Original Baudot code, continental European variant (letter set, switched to with 0x10)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL A E É Y U I O FIGS J G H B C F D
1x  SP  ṯ X Z S T W V DEL K M L R Q N P
Original Baudot code, continental variant (figure set, switched to with 0x08)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL 1 2 & 3 4 º 5  SP  6 7 H̱ 8 9 F̱ 0
1x LTRS . , : ; ! ? ' DEL ( ) = - / № %

Original Baudot, ITA 1

ITA 1 (letter set, switched to with 0x10)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL A E  CR  Y U I O FIGS J G H B C F D
1x  SP   LF  X Z S T W V DEL K M L R Q N P
ITA 1 (figure set, switched to with 0x08)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL 1 2  CR  3 4 PU[a] 5  SP  6 7 + 8 9 PU[a] 0
1x LTRS  LF  , : . PU[a] ? ' DEL ( ) = - / PU[a] %

Baudot–Murray variants

Murray Code

Murray code (letter set, switched to with 0x04)[21]
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL/ SP  E COL A LTRS S I U  LF  D R J N F C K
1x T Z L W H Y P Q O B G FIGS M X V DEL/*[b]
Murray code (figure set, switched to with 0x1B)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL/ SP  3 COL LTRS ' 8 7  LF  ² 4 ⁷⁄ − ⅟ ( ⁹⁄
1x 5 . / 2 ⁵⁄ 6 0 1 9 ? ³⁄ FIGS , £ ) DEL/*[b]

ITA 2 and US-TTY

ITA2 and US-TTY Baudot–Murray code (letter set, switched to with 0x1F)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL E  LF  A  SP  S I U  CR  D R J N F C K
1x T Z L W H Y P Q O B G FIGS M X V LTRS/DEL
US-TTY Baudot–Murray code (figure set, switched to with 0x1B)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL 3  LF  −  SP  BEL 8 7  CR  $ 4 ' , ! : (
1x 5 " ) 2 # 6 0 1 9 ? & FIGS . / ; LTRS
ITA2 Baudot–Murray code (figure set, switched to with 0x1B)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x NUL 3  LF  −  SP  ' 8 7  CR  ENQ 4 BEL , ! : (
1x 5 + ) 2 £ 6 0 1 9 ? & FIGS . / = LTRS

Weather code

Meteorologists used a variant of ITA2 with the figures-case symbols, except for the ten digits, BEL and a few other characters, replaced by weather symbols:

 
Weather teleprinter encoding
Meteorological Baudot–Murray code (figure set, switched to with 0x1B)
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x - 3  LF  ↑  SP  BEL 8 7  CR  ↗ 4 ↙ ⦷ → ◯ ←
1x 5 + ↖ 2 ↓ 6 0 1 9 ⊕ ↘ FIGS . / ⦶ LTRS

Details

Note: This table presumes the space called "1" by Baudot and Murray is rightmost, and least significant. The way the transmitted bits were packed into larger codes varied by manufacturer. The most common solution allocates the bits from the least significant bit towards the most significant bit (leaving the three most significant bits of a byte unused).

 
Table of ITA2 codes (expressed as hexadecimal numbers)

In ITA2, characters are expressed using five bits. ITA2 uses two code sub-sets, the "letter shift" (LTRS), and the "figure shift" (FIGS). The FIGS character (11011) signals that the following characters are to be interpreted as being in the FIGS set, until this is reset by the LTRS (11111) character. In use, the LTRS or FIGS shift key is pressed and released, transmitting the corresponding shift character to the other machine. The desired letters or figures characters are then typed. Unlike a typewriter or modern computer keyboard, the shift key isn't kept depressed whilst the corresponding characters are typed. "ENQuiry" will trigger the other machine's answerback. It means "Who are you?"

CR is carriage return, LF is line feed, BEL is the bell character which rang a small bell (often used to alert operators to an incoming message), SP is space, and NUL is the null character (blank tape).

Note: the binary conversions of the codepoints are often shown in reverse order, depending on (presumably) from which side one views the paper tape. Note further that the "control" characters were chosen so that they were either symmetric or in useful pairs so that inserting a tape "upside down" did not result in problems for the equipment and the resulting printout could be deciphered. Thus FIGS (11011), LTRS (11111) and space (00100) are invariant, while CR (00010) and LF (01000), generally used as a pair, are treated the same regardless of order by page printers.[22] LTRS could also be used to overpunch characters to be deleted on a paper tape (much like DEL in 7-bit ASCII).

The sequence RYRYRY... is often used in test messages, and at the start of every transmission. Since R is 01010 and Y is 10101, the sequence exercises much of a teleprinter's mechanical components at maximum stress. Also, at one time, fine-tuning of the receiver was done using two coloured lights (one for each tone). 'RYRYRY...' produced 0101010101..., which made the lights glow with equal brightness when the tuning was correct. This tuning sequence is only useful when ITA2 is used with two-tone FSK modulation, such as is commonly seen in radioteletype (RTTY) usage.

US implementations of Baudot code may differ in the addition of a few characters, such as #, & on the FIGS layer.

The Russian version of Baudot code (MTK-2) used three shift modes; the Cyrillic letter mode was activated by the character (00000). Because of the larger number of characters in the Cyrillic alphabet, the characters !, &, £ were omitted and replaced by Cyrillics, and BEL has the same code as Cyrillic letter Ю. The Cyrillic letters Ъ and Ё are omitted, and Ч is merged with the numeral 4.

See also

Notes

  1. ^ a b c d "At the disposal of each administration for its internal service"[21]
  2. ^ a b "[G]ives invisible correction on page printers & * on slip printers."[21]

References

  1. ^ Ralston, Anthony; Reilly, Edwin D., eds. (1993), "Baudot Code", Encyclopedia of Computer Science (Third ed.), New York: IEEE Press/Van Nostrand Reinhold, ISBN 0-442-27679-6
  2. ^ a b H. A. Emmons (1 May 1916). "Printer Systems". Wire & Radio Communications. 34: 209.
  3. ^ a b c Fischer, Eric N. (20 June 2000). "The Evolution of Character Codes, 1874–1968". ark:/13960/t07x23w8s. Retrieved 20 December 2020. [...] In 1872, [Baudot] started research toward a telegraph system that would allow multiple operators to transmit simultaneously over a single wire and, as the transmissions were received, would print them in ordinary alphabetic characters on a strip of paper. He received a patent for such a system on June 17, 1874. [...] Instead of a variable delay followed by a single-unit pulse, Baudot's system used a uniform six time units to transmit each character. [...] his early telegraph probably used the six-unit code [...] that he attributes to Davy in an 1877 article. [...] in 1876 Baudot redesigned his equipment to use a five-unit code. Punctuation and digits were still sometimes needed, though, so he adopted from Hughes the use of two special letter space and figure space characters that would cause the printer to shift between cases at the same time as it advanced the paper without printing. The five-unit code he began using at this time [...] was structured to suit his keyboard [...], which controlled two units of each character with switches operated by the left hand and the other three units with the right hand. [...] [2]
  4. ^ Baudot, Jean-Maurice-Émile (June 1874). (in French). Archives Institut National de la Propriété Industrielle (INPI). Patent Brevet 103,898. Archived from the original on 16 December 2017.
  5. ^ William V. Vansize (25 January 1901). "A New Page-Printing Telegraph". Transactions. American Institute of Electrical Engineers. 18: 22.
  6. ^ Procès d'Amiens Baudot vs Mimault
  7. ^ a b Jennings, Tom (2020). "An annotated history of some character codes: Baudot's code".
  8. ^ Beauchamp, K.G. (2001). History of Telegraphy: Its Technology and Application. Institution of Engineering and Technology. pp. 394–395. ISBN 0-85296-792-6.
  9. ^ Alan G. Hobbs, 5 Unit Codes, section Baudot Multiplex System
  10. ^ Gleick, James (2011). The Information: A History, a Theory, a Flood. London: Fourth Estate. p. 203. ISBN 978-0-00-742311-8.
  11. ^ Foster, Maximilian (August 1901). "A Successful Printing Telegraph". The World's Work: A History of Our Time. II: 1195–1199. Retrieved 9 July 2009.
  12. ^ Copeland 2006, p. 38
  13. ^ Telegraph and Telephone Age. 1921. I allocated the most frequently used letters in English language to the signals represented by the fewest holes in the perforated tape, and so on in proportion.
  14. ^ "BruXy: Radio Teletype communication". 10 October 2005. Retrieved 9 May 2016. The transmitted code use International Telegraph Alphabet No. 2 (ITA-2) which was introduced by CCITT in 1924.
  15. ^ Smith, Gil (2001). "Teletype Communication Codes" (PDF). Baudot.net. (PDF) from the original on 20 August 2008. Retrieved 11 July 2008.
  16. ^ a b Steinbuch, Karl W.; Weber, Wolfgang, eds. (1974) [1967]. Taschenbuch der Informatik - Band III - Anwendungen und spezielle Systeme der Nachrichtenverarbeitung. Taschenbuch der Nachrichtenverarbeitung (in German). Vol. 3 (3 ed.). Berlin, Germany: Springer Verlag. pp. 328–329. ISBN 3-540-06242-4. LCCN 73-80607.
  17. ^ dataIP Limited. . Archived from the original on 23 December 2017. Retrieved 16 July 2017.
  18. ^ ITU-T Recommendation S.2 / 11/1988, published in Fascicle VII.1 of the Blue Book
  19. ^ (PDF). Deutsche Börse. 17 May 2010. Archived from the original (PDF) on 8 February 2012. Retrieved 10 August 2011.
  20. ^ Gillam, Richard (2002). Unicode Demystified. Addison-Wesley. p. 30. ISBN 0-201-70052-2.
  21. ^ a b c d e f g h i . NADCOMM museum. Archived from the original on 4 November 1999. Retrieved 5 December 2001.
  22. ^ Jennings, Tom (5 February 2020). "An annotated history of some character codes: ITA2". Retrieved 1 June 2022. [...] the characters that are 'transmission control' related [...] are bit-wise symmetrical – the codes for FIGS, LTRS, space and BLANK – are the same reversed left to right! Further, the codes for CR and LF, equal each other when reversed left to right!
  23. ^ Bacon, Francis (1605). The Proficience and Advancement of Learning Divine and Humane.

Further reading

  • Copeland, B. Jack, ed. (2006). Colossus: The Secrets of Bletchley Park's Codebreaking Computers. Oxford: Oxford University Press. ISBN 978-0-19-284055-4.
  • Hobbs, Alan G. "NADCOMM Papers and Writings: Five-unit codes". Retrieved 10 February 2017.
  • MTK-2 code table
  • Baudot, Murray, ITA2, ITA5, etc.
  • . Archived from the original on 13 September 2009.
  • Online Baudot code converter (includes paper tape view)
  • A breakdown of the patent for Baudot's first device

January 07, 2023
baudot, code, boˈdo, early, character, encoding, telegraphy, invented, Émile, baudot, 1870s, predecessor, international, telegraph, alphabet, ita2, most, common, teleprinter, code, until, advent, ascii, each, character, alphabet, represented, series, five, bit. The Baudot code boˈdo is an early character encoding for telegraphy invented by Emile Baudot in the 1870s 1 It was the predecessor to the International Telegraph Alphabet No 2 ITA2 the most common teleprinter code in use until the advent of ASCII Each character in the alphabet is represented by a series of five bits sent over a communication channel such as a telegraph wire or a radio signal by asynchronous serial communication The symbol rate measurement is known as baud and is derived from the same name An early piano Baudot keyboard Contents 1 History 1 1 Baudot code ITA1 1 2 Murray code 1 3 Western Union 1 4 ITA2 2 Nomenclature 3 Character set 3 1 Original Baudot variants 3 1 1 Original Baudot domestic UK 3 1 2 Original Baudot Continental European 3 1 3 Original Baudot ITA 1 3 2 Baudot Murray variants 3 2 1 Murray Code 3 2 2 ITA 2 and US TTY 3 3 Weather code 4 Details 5 See also 6 Notes 7 References 8 Further readingHistory EditBaudot code ITA1 Edit Baudot code ITA1 An early version from Baudot s 1888 US patent listing A through Z t and Erasure Alias es International Telegraph Alphabet 1Current statusReplaced by ITA2 not mutually compatible Classification5 bit stateful basic Latin encodingPreceded byMorse codeSucceeded byITA2vteIn the below table Columns I II III IV and V show the code the Let and Fig columns show the letters and numbers for the Continental and UK versions and the sort keys present the table in the order alphabetical Gray and UK Baudot code Continental and UK versions Europe sort keys UK sort keysV IV I II III Con ti nen tal Gray Let Fig V IV I II III UK A 1 A 1 E amp 1 E 2 E 2 I o I 3 O 5 O 5 U 4 U 4 Y 3 Y 3 B 8 B 8 C 9 C 9 D 0 D 0 F f F 5 G 7 G 7 H h H J 6 J 6 Figure Blank Fig Bl Erasure Erasure K K L L M M N N N P P Q Q R R S S 7 T T V V W W X X 9 Z Z t Blank Letter Bl Let Baudot developed his first multiplexed telegraph in 1872 2 3 and patented it in 1874 3 4 In 1876 he changed from a six bit code to a five bit code 3 as suggested by Carl Friedrich Gauss and Wilhelm Weber in 1834 2 5 with equal on and off intervals which allowed for transmission of the Roman alphabet and included punctuation and control signals The code itself was not patented only the machine because French patent law does not allow concepts to be patented 6 Baudot s 5 bit code was adapted to be sent from a manual keyboard and no teleprinter equipment was ever constructed that used it in its original form 7 The code was entered on a keyboard which had just five piano type keys and was operated using two fingers of the left hand and three fingers of the right hand Once the keys had been pressed they were locked down until mechanical contacts in a distributor unit passed over the sector connected to that particular keyboard at which time the keyboard was unlocked ready for the next character to be entered with an audible click known as the cadence signal to warn the operator Operators had to maintain a steady rhythm and the usual speed of operation was 30 words per minute 8 The table shows the allocation of the Baudot code which was employed in the British Post Office for continental and inland services A number of characters in the continental code are replaced by fractionals in the inland code Code elements 1 2 and 3 are transmitted by keys 1 2 and 3 and these are operated by the first three fingers of the right hand Code elements 4 and 5 are transmitted by keys 4 and 5 and these are operated by the first two fingers of the left hand 7 9 10 Baudot s code became known as the International Telegraph Alphabet No 1 ITA1 It is no longer used Murray code Edit Paper tape with holes representing the Baudot Murray Code Note the fully punched columns of Delete Letters select codes at end of the message on the right which were used to cut the band easily between distinct messages The last symbols before the fully punched columns at the end are BRASIL CR LF CR FS word Brasil carriage return line feed carriage return shift to figures In 1901 Baudot s code was modified by Donald Murray 1865 1945 prompted by his development of a typewriter like keyboard The Murray system employed an intermediate step a keyboard perforator which allowed an operator to punch a paper tape and a tape transmitter for sending the message from the punched tape At the receiving end of the line a printing mechanism would print on a paper tape and or a reperforator could be used to make a perforated copy of the message 11 As there was no longer a connection between the operator s hand movement and the bits transmitted there was no concern about arranging the code to minimize operator fatigue and instead Murray designed the code to minimize wear on the machinery assigning the code combinations with the fewest punched holes to the most frequently used characters 12 13 For example the one hole letters are E and T The ten two hole letters are AOINSHRDLZ very similar to the Etaoin shrdlu order used in Linotype machines Ten more letters BCGFJMPUWY have three holes each and the four hole letters are VXKQ The Murray code also introduced what became known as format effectors or control characters the CR Carriage Return and LF Line Feed codes A few of Baudot s codes moved to the positions where they have stayed ever since the NULL or BLANK and the DEL code NULL BLANK was used as an idle code for when no messages were being sent but the same code was used to encode the space separation between words Sequences of DEL codes fully punched columns were used at start or end of messages or between them allowing easy separation of distinct messages BELL codes could be inserted in those sequences to signal to the remote operator that a new message was coming or that transmission of a message was terminated Early British Creed machines also used the Murray system Western Union Edit Keyboard of a teleprinter using the Baudot code US variant with FIGS and LTRS shift keys Murray s code was adopted by Western Union which used it until the 1950s with a few changes that consisted of omitting some characters and adding more control codes An explicit SPC space character was introduced in place of the BLANK NULL and a new BEL code rang a bell or otherwise produced an audible signal at the receiver Additionally the WRU or Who aRe yoU code was introduced which caused a receiving machine to send an identification stream back to the sender ITA2 Edit ITA2 Baudot Murray code British variant of ITA2Alias es International Telegraph Alphabet 2Classification5 bit stateful basic Latin encodingPreceded byITA1Succeeded byFIELDATA ITA 3 van Duuren code ITA 5 ISO 646 ASCII vteMTK 2Language s RussianClassification5 bit stateful Russian Cyrillic encodingPreceded byRussian Morse codeSucceeded byKOI 7vteIn 1924 the CCITT introduced the International Telegraph Alphabet No 2 ITA2 code 14 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 15 Some code points marked blue in the table were reserved for national specific usage 16 A four row teletype keyboard with Roman and Cyrillic letters International telegraphy alphabet No 2 Baudot Murray code 17 Impulse patterns 1 mark 0 space Letter shift Figure shiftLSB on right code elements 543 21 LSB on left code elements 12 345 Count of punched marks ITA2 standard RussianMTK 2 variant RussianMTK 2 variant ITA2 standard US TTY variant000 00 00 000 0 Null Shift to Cyrillic Letters Null010 00 00 010 1 Carriage return000 10 01 000 1 Line feed001 00 00 100 1 Space101 11 11 101 4 Q Ya 1100 11 11 001 3 W V 2000 01 10 000 1 E E 3010 10 01 010 2 R R 4100 00 00 001 1 T T 5101 01 10 101 3 Y Y 6001 11 11 100 3 U U 7001 10 01 100 2 I I 8110 00 00 011 2 O O 9101 10 01 101 3 P P 0000 11 11 000 2 A A 001 01 10 100 2 S S Bell010 01 10 010 2 D D WRU 011 01 10 110 3 F F E 110 10 01 011 3 G G Sh amp 101 00 00 101 2 H H Sh 010 11 11 010 3 J J Yu Bell 011 11 11 110 4 K K 100 10 01 001 2 L L 100 01 10 001 2 Z Z 111 01 10 111 4 X 011 10 01 110 3 C C 111 10 01 111 4 V Zh 110 01 10 011 3 B B 011 00 00 110 2 N N 111 00 00 111 3 M M 110 11 11 011 4 Shift to Figures FS Reserved for figures extension111 11 11 111 5 Reserved for lettercase extension Shift to Letters LS Erasure DeleteThe 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 16 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 clarification needed 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 18 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 Borse to reduce the character encoding footprint 19 Nomenclature EditNearly all 20th century teleprinter equipment used Western Union s code ITA2 or variants thereof Radio amateurs casually call ITA2 and variants Baudot incorrectly 20 and even the American Radio Relay League s Amateur Radio Handbook does so though in more recent editions the tables of codes correctly identifies it as ITA2 Character set EditThe values shown in each cell are the Unicode codepoints given for comparison Original Baudot variants Edit Original Baudot domestic UK Edit Original Baudot code UK domestic variant letter set switched to with 0x10 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL A E Y U I O FIGS J G H B C F D1x SP X Z S T W V DEL K M L R Q N POriginal Baudot code UK domestic variant figure set switched to with 0x08 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL 1 2 3 4 5 SP 6 7 8 9 01x LTRS DEL Original Baudot Continental European Edit Original Baudot code continental European variant letter set switched to with 0x10 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL A E E Y U I O FIGS J G H B C F D1x SP ṯ X Z S T W V DEL K M L R Q N POriginal Baudot code continental variant figure set switched to with 0x08 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL 1 2 amp 3 4 º 5 SP 6 7 H 8 9 F 01x LTRS DEL Original Baudot ITA 1 Edit ITA 1 letter set switched to with 0x10 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL A E CR Y U I O FIGS J G H B C F D1x SP LF X Z S T W V DEL K M L R Q N PITA 1 figure set switched to with 0x08 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL 1 2 CR 3 4 PU a 5 SP 6 7 8 9 PU a 01x LTRS LF PU a DEL PU a Baudot Murray variants Edit Murray Code Edit Murray code letter set switched to with 0x04 21 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL SP E COL A LTRS S I U LF D R J N F C K1x T Z L W H Y P Q O B G FIGS M X V DEL b Murray code figure set switched to with 0x1B 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL SP 3 COL LTRS 8 7 LF 4 1x 5 2 6 0 1 9 FIGS DEL b ITA 2 and US TTY Edit ITA2 and US TTY Baudot Murray code letter set switched to with 0x1F 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL E LF A SP S I U CR D R J N F C K1x T Z L W H Y P Q O B G FIGS M X V LTRS DELUS TTY Baudot Murray code figure set switched to with 0x1B 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL 3 LF SP BEL 8 7 CR 4 1x 5 2 6 0 1 9 amp FIGS LTRSITA2 Baudot Murray code figure set switched to with 0x1B 0 1 2 3 4 5 6 7 8 9 A B C D E F0x NUL 3 LF SP 8 7 CR ENQ 4 BEL 1x 5 2 6 0 1 9 amp FIGS LTRSWeather code Edit Meteorologists used a variant of ITA2 with the figures case symbols except for the ten digits BEL and a few other characters replaced by weather symbols Weather teleprinter encoding Meteorological Baudot Murray code figure set switched to with 0x1B 0 1 2 3 4 5 6 7 8 9 A B C D E F0x 3 LF SP BEL 8 7 CR 4 1x 5 2 6 0 1 9 FIGS LTRSDetails EditNote This table presumes the space called 1 by Baudot and Murray is rightmost and least significant The way the transmitted bits were packed into larger codes varied by manufacturer The most common solution allocates the bits from the least significant bit towards the most significant bit leaving the three most significant bits of a byte unused Table of ITA2 codes expressed as hexadecimal numbers In ITA2 characters are expressed using five bits ITA2 uses two code sub sets the letter shift LTRS and the figure shift FIGS The FIGS character 11011 signals that the following characters are to be interpreted as being in the FIGS set until this is reset by the LTRS 11111 character In use the LTRS or FIGS shift key is pressed and released transmitting the corresponding shift character to the other machine The desired letters or figures characters are then typed Unlike a typewriter or modern computer keyboard the shift key isn t kept depressed whilst the corresponding characters are typed ENQuiry will trigger the other machine s answerback It means Who are you CR is carriage return LF is line feed BEL is the bell character which rang a small bell often used to alert operators to an incoming message SP is space and NUL is the null character blank tape Note the binary conversions of the codepoints are often shown in reverse order depending on presumably from which side one views the paper tape Note further that the control characters were chosen so that they were either symmetric or in useful pairs so that inserting a tape upside down did not result in problems for the equipment and the resulting printout could be deciphered Thus FIGS 11011 LTRS 11111 and space 00100 are invariant while CR 00010 and LF 01000 generally used as a pair are treated the same regardless of order by page printers 22 LTRS could also be used to overpunch characters to be deleted on a paper tape much like DEL in 7 bit ASCII The sequence RYRYRY is often used in test messages and at the start of every transmission Since R is 01010 and Y is 10101 the sequence exercises much of a teleprinter s mechanical components at maximum stress Also at one time fine tuning of the receiver was done using two coloured lights one for each tone RYRYRY produced 0101010101 which made the lights glow with equal brightness when the tuning was correct This tuning sequence is only useful when ITA2 is used with two tone FSK modulation such as is commonly seen in radioteletype RTTY usage US implementations of Baudot code may differ in the addition of a few characters such as amp on the FIGS layer The Russian version of Baudot code MTK 2 used three shift modes the Cyrillic letter mode was activated by the character 00000 Because of the larger number of characters in the Cyrillic alphabet the characters amp were omitted and replaced by Cyrillics and BEL has the same code as Cyrillic letter Yu The Cyrillic letters and Yo are omitted and Ch is merged with the numeral 4 See also EditBacon s cipher A 5 bit binary encoding of the English alphabet devised by Francis Bacon in 1605 23 List of information system character sets CCIR 476Notes Edit a b c d At the disposal of each administration for its internal service 21 a b G ives invisible correction on page printers amp on slip printers 21 References Edit Ralston Anthony Reilly Edwin D eds 1993 Baudot Code Encyclopedia of Computer Science Third ed New York IEEE Press Van Nostrand Reinhold ISBN 0 442 27679 6 a b H A Emmons 1 May 1916 Printer Systems Wire amp Radio Communications 34 209 a b c Fischer Eric N 20 June 2000 The Evolution of Character Codes 1874 1968 ark 13960 t07x23w8s Retrieved 20 December 2020 In 1872 Baudot started research toward a telegraph system that would allow multiple operators to transmit simultaneously over a single wire and as the transmissions were received would print them in ordinary alphabetic characters on a strip of paper He received a patent for such a system on June 17 1874 Instead of a variable delay followed by a single unit pulse Baudot s system used a uniform six time units to transmit each character his early telegraph probably used the six unit code that he attributes to Davy in an 1877 article in 1876 Baudot redesigned his equipment to use a five unit code Punctuation and digits were still sometimes needed though so he adopted from Hughes the use of two special letter space and figure space characters that would cause the printer to shift between cases at the same time as it advanced the paper without printing The five unit code he began using at this time was structured to suit his keyboard which controlled two units of each character with switches operated by the left hand and the other three units with the right hand 1 2 Baudot Jean Maurice Emile June 1874 Systeme de telegraphie rapide in French Archives Institut National de la Propriete Industrielle INPI Patent Brevet 103 898 Archived from the original on 16 December 2017 William V Vansize 25 January 1901 A New Page Printing Telegraph Transactions American Institute of Electrical Engineers 18 22 Proces d Amiens Baudot vs Mimault a b Jennings Tom 2020 An annotated history of some character codes Baudot s code Beauchamp K G 2001 History of Telegraphy Its Technology and Application Institution of Engineering and Technology pp 394 395 ISBN 0 85296 792 6 Alan G Hobbs 5 Unit Codes section Baudot Multiplex System Gleick James 2011 The Information A History a Theory a Flood London Fourth Estate p 203 ISBN 978 0 00 742311 8 Foster Maximilian August 1901 A Successful Printing Telegraph The World s Work A History of Our Time II 1195 1199 Retrieved 9 July 2009 Copeland 2006 p 38 Telegraph and Telephone Age 1921 I allocated the most frequently used letters in English language to the signals represented by the fewest holes in the perforated tape and so on in proportion BruXy Radio Teletype communication 10 October 2005 Retrieved 9 May 2016 The transmitted code use International Telegraph Alphabet No 2 ITA 2 which was introduced by CCITT in 1924 Smith Gil 2001 Teletype Communication Codes PDF Baudot net Archived PDF from the original on 20 August 2008 Retrieved 11 July 2008 a b Steinbuch Karl W Weber Wolfgang eds 1974 1967 Taschenbuch der Informatik Band III Anwendungen und spezielle Systeme der Nachrichtenverarbeitung Taschenbuch der Nachrichtenverarbeitung in German Vol 3 3 ed Berlin Germany Springer Verlag pp 328 329 ISBN 3 540 06242 4 LCCN 73 80607 dataIP Limited The Baudot Code Archived from the original on 23 December 2017 Retrieved 16 July 2017 ITU T Recommendation S 2 11 1988 published in Fascicle VII 1 of the Blue Book Enhanced Broadcast Solution Interface Specification Final Version PDF Deutsche Borse 17 May 2010 Archived from the original PDF on 8 February 2012 Retrieved 10 August 2011 Gillam Richard 2002 Unicode Demystified Addison Wesley p 30 ISBN 0 201 70052 2 a b c d e f g h i Five unit codes NADCOMM museum Archived from the original on 4 November 1999 Retrieved 5 December 2001 Jennings Tom 5 February 2020 An annotated history of some character codes ITA2 Retrieved 1 June 2022 the characters that are transmission control related are bit wise symmetrical the codes for FIGS LTRS space and BLANK are the same reversed left to right Further the codes for CR and LF equal each other when reversed left to right Bacon Francis 1605 The Proficience and Advancement of Learning Divine and Humane Further reading Edit Wikimedia Commons has media related to Baudot code Copeland B Jack ed 2006 Colossus The Secrets of Bletchley Park s Codebreaking Computers Oxford Oxford University Press ISBN 978 0 19 284055 4 Hobbs Alan G NADCOMM Papers and Writings Five unit codes Retrieved 10 February 2017 MTK 2 code table Baudot Murray ITA2 ITA5 etc Jean Maurice Emile Baudot Archived from the original on 13 September 2009 Online Baudot code converter includes paper tape view A breakdown of the patent for Baudot s first device Retrieved from https en wikipedia org w index php title Baudot code amp oldid 1100190272, wikipedia, wiki, book, books, library,

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