Baudot code: Difference between revisions
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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.<ref>Procès d'Amiens Baudot vs Mimault</ref> | 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.<ref>Procès d'Amiens Baudot vs Mimault</ref> | ||
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.<ref name = "TomJennings-Baudot">{{Cite web |last1=Jennings |first1=Tom |author-link=Tom Jennings |title=An annotated history of some character codes: Baudot's code |year=2020 |url=https://www. | 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.<ref name = "TomJennings-Baudot">{{Cite web |last1=Jennings |first1=Tom |author-link=Tom Jennings |title=An annotated history of some character codes: Baudot's code |year=2020 |url=https://www.sensitiveresearch.com/Archive/CharCodeHist/index.html#BAUDOT |access-date=20 September 2025}}</ref> 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.<ref>{{cite book |last=Beauchamp |first=K.G. |title=History of Telegraphy: Its Technology and Application |publisher=[[Institution of Engineering and Technology]] |year=2001 |pages=394–395 |isbn=0-85296-792-6}}</ref> | ||
The table "shows the allocation of the Baudot code which was employed in the [[General Post Office#New communication systems|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."<ref name = "TomJennings-Baudot" /><ref>Alan G. Hobbs, ''[http://www.nadcomm.com/?p=95 5 Unit Codes]'', section ''Baudot Multiplex System''</ref><ref>{{cite book |last=Gleick |first=James |title=The Information: A History, a Theory, a Flood |year=2011 |publisher=Fourth Estate |location=London |isbn=978-0-00-742311-8 |pages=203 |url=http://around.com/the-information}}</ref> | The table "shows the allocation of the Baudot code which was employed in the [[General Post Office#New communication systems|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."<ref name = "TomJennings-Baudot" /><ref>Alan G. Hobbs, ''[http://www.nadcomm.com/?p=95 5 Unit Codes]'', section ''Baudot Multiplex System''</ref><ref>{{cite book |last=Gleick |first=James |title=The Information: A History, a Theory, a Flood |year=2011 |publisher=Fourth Estate |location=London |isbn=978-0-00-742311-8 |pages=203 |url=http://around.com/the-information}}</ref> | ||
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===Western Union=== | ===Western Union=== | ||
[[File:Baudotkeyboard.png|right|frame|Keyboard of a [[teleprinter]] using the Baudot code (US variant), with FIGS and LTRS shift keys]] | [[File:Baudotkeyboard.png|right|frame|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 [[Bell character|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. | 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 [[Bell character|BEL]] code rang a bell or otherwise produced an audible signal at the receiver. Additionally, the [[Enquiry character|WRU]] or "Who aRe yoU?" code was introduced, which caused a receiving machine to send an identification stream back to the sender. | ||
{{clear}} | {{clear}} | ||
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| 001·01 || 10·100 || 2 || S || С ||colspan="2"| ' ||style="background:#FCC"| Bell | | 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> || $ | | 010·01 || 10·010 || 2 || D || Д ||colspan="2"| [[enquiry character|<abbr title="Who are you?">WRU?</abbr>]] || $ | ||
|- | |- | ||
| 011·01 || 10·110 || 3 || F || Ф || style="background:#CCF"|Э || style="background:#CCF" colspan="2"| ! | | 011·01 || 10·110 || 3 || F || Ф || style="background:#CCF"|Э || style="background:#CCF" colspan="2"| ! | ||
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CR is [[carriage return]], LF is [[line feed]], BEL is the [[bell character]] which rang a small [[bell (instrument)|bell]] (often used to alert operators to an incoming message), SP is space, and NUL is the [[null character]] (blank tape). | CR is [[carriage return]], LF is [[line feed]], BEL is the [[bell character]] which rang a small [[bell (instrument)|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 character|"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.<ref>{{cite web|url=https://www. | 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 character|"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.<ref>{{cite web |url=https://www.sensitiveresearch.com/Archive/CharCodeHist/index.html#ITA2 |title=An annotated history of some character codes: ITA2 |last=Jennings |first=Tom |author-link=Tom Jennings |date=5 February 2020 |access-date=20 September 2025 |quote=[...] 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!}}</ref> LTRS could also be used to overpunch characters to be deleted on a paper tape (much like DEL in 7-bit [[ASCII]]). | ||
The sequence ''[[RY (test signal)|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 [[Frequency-shift keying|FSK]] modulation, such as is commonly seen in [[radioteletype]] (RTTY) usage. | The sequence ''[[RY (test signal)|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 [[Frequency-shift keying|FSK]] modulation, such as is commonly seen in [[radioteletype]] (RTTY) usage. | ||