Baudot code

The Baudot code [bodo], invented by Émile Baudot,[1] is a character set predating EBCDIC and ASCII. It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the 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. The symbol rate measurement is known as baud, and is derived from the same name.

Clavier Baudot
An early "piano" Baudot keyboard

History

Baudot code (ITA1)

Baudot code (ITA1)
Baudot Code - from 1888 patent
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

Technically, five-bit codes began in the 17th century, when Francis Bacon developed the cipher now called Bacon's cipher. The cipher was not designed for machine telecommunications (it was instead a method of encrypting a hidden message into another) and, although in theory it could be adapted to that purpose, it only covered 24 of the 26 letters of the English alphabet (two sets of letters, I/J and U/V, were expressed with the same code) and contained no punctuation, spaces, numbers or control characters, rendering it of little use.[2]

Baudot invented his original code in 1870 and patented it in 1874.[3] It was a 5-bit code, with equal on and off intervals, which allowed for transmission of the Roman alphabet, and included punctuation and control signals. It was based on an earlier code developed by Carl Friedrich Gauss and Wilhelm Weber in 1834.[4][5][6] It was a Gray code (when vowels and consonants are sorted in their alphabetical order),[7] nonetheless, the code by itself was not patented (only the machine) because French patent law does not allow concepts to be patented.[8]

Baudot's original code was adapted to be sent from a manual keyboard, and no teleprinter equipment was ever constructed that used it in its original form.[9] 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, when 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.[10]

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."[9][11][12]

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

Murray code

Baudot Tape
Paper tape with holes representing the "Baudot–Murray Code". Note the fully punched columns of "Delete/Letters select" codes at start of the message (on the right); were used to cut the band easily between distinct messages. The message then starts with a figure shift control followed by a carriage return.

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.[13] 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.[14][15]

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 have three holes, 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 used the Murray system.

Western Union

Baudotkeyboard
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
International Telegraph Alphabet 2
British variant of ITA2
Alias(es)International Telegraph Alphabet 2
Classification5-bit stateful basic Latin encoding
Preceded byITA1
Succeeded byFIELDATA,
ITA 5 (US-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[16] 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.[17]

Some code points (marked blue in the table) were reserved for national-specific usage.[18]

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 group of five pulses, which could also be detected by simple passive electronic devices to turn on the teleprinter; this series of pulse was generating series of Erasure/Delete and also initializing the receiver state 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 opposite 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.[18]

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 a safe destruction of the message before recycling the punched band. For that function, it also plays the same role of filler as the Delete code in ASCII (and also in other 7-bit or 8-bit encodings, including EBCDIC for punched cards). Once codes for a fragment text has been replaced by 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 may be arbitrarily inserted near the end of a punch band or at start of it, and has to be ignored, whereas the Space code is significant in text).

The cells marked as reserved for extensions (using the LS code again from the letters shift page, just after a first LS code to shift from the figures page) has been defined to shift into a new mode: in this new mode, the letters page are containing lowercase letters only, but a third page of codes is still accessible for the uppercase letters, either temporarily for a single letter (encode LS before that letter), may be locked (with FS+LS) for an unlimited number of capital letters or digits and then unlocked to return to lowercase mode (with a single LS).[20] 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 uppercased 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.[21]

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,[22] 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

Original Baudot variants

Original Baudot, domestic UK

Original Baudot code, UK domestic variant (letter set, switched to with 0x10)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
A
0041
E
0045
/
002F
Y
0059
U
0055
I
0049
O
004F
FS
000E
J
004A
G
0047
H
0048
B
0042
C
0043
F
0046
D
0044
1_ SP
0020
-
002D
X
0058
Z
005A
S
0053
T
0054
W
0057
V
0056
DEL
007F
K
004B
M
004D
L
004C
R
0052
Q
0051
N
004E
P
0050
Original Baudot code, UK domestic variant (figure set, switched to with 0x08)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
1
0031
2
0032

215F
3
0033
4
0034
³⁄
00B3 2044
5
0035
SP
0020
6
0036
7
0037
¹
00B9
8
0038
9
0039
⁵⁄
2075 2044
0
0030
1_ LS
000F
.
002E
⁹⁄
2079 2044
:
003A
⁷⁄
2077 2044
²
00B2
?
003F
'
0027
DEL
007F
(
0028
)
0029
=
003D
-
002D
/
002F
£
00A3
+
002B

Original Baudot, Continental European

Original Baudot code, continental European variant (letter set, switched to with 0x10)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
A
0041
E
0045
É
00C9
Y
0059
U
0055
I
0049
O
004F
FS
000E
J
004A
G
0047
H
0048
B
0042
C
0043
F
0046
D
0044
1_ SP
0020
t
0074
X
0058
Z
005A
S
0053
T
0054
W
0057
V
0056
DEL
007F
K
004B
M
004D
L
004C
R
0052
Q
0051
N
004E
P
0050
Original Baudot code, continental variant (figure set, switched to with 0x08)[23][23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
1
0031
2
0032
&
0026
3
0033
4
0034
º
00BA
5
0035
SP
0020
6
0036
7
0037
h
0068
8
0038
9
0039
f
0066
0
0030
1_ LS
000F
.
002E
,
002C
:
003A
;
003B
!
0021
?
003F
'
0027
DEL
007F
(
0028
)
0029
=
003D
-
002D
/
002F

2116
%
0025

Original Baudot, ITA 1

ITA 1 (letter set, switched to with 0x10)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
A
0041
E
0045
CR
000D
Y
0059
U
0055
I
0049
O
004F
FS
000E
J
004A
G
0047
H
0048
B
0042
C
0043
F
0046
D
0044
1_ SP
0020
LF
000A
X
0058
Z
005A
S
0053
T
0054
W
0057
V
0056
DEL
007F
K
004B
M
004D
L
004C
R
0052
Q
0051
N
004E
P
0050
ITA 1 (figure set, switched to with 0x08)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL
0000
1
0031
2
0032
CR
000D
3
0033
4
0034
PU
[a]
5
0035
SP
0020
6
0036
7
0037
+
002B
8
0038
9
0039
PU
[a]
0
0030
1_ LS
000F
LF
000A
,
002C
:
003A
.
002E
PU
[a]
?
003F
'
0027
DEL
007F
(
0028
)
0029
=
003D
-
002D
/
002F
PU
[a]
%
0025

Baudot-Murray variants

Murray Code

Murray code (letter set, switched to with 0x04)[23]
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL/SP
0000/0020
E
0045
COL
?
A
0041
LS
000F
S
0053
I
0049
U
0055
LF
000A
D
0044
R
0052
J
004A
N
004E
F
0046
C
0043
K
004B
1_ T
0054
Z
005A
L
004C
W
0057
H
0048
Y
0059
P
0050
Q
0051
O
004F
B
0042
G
0047
FS
000E
M
004D
X
0058
V
0056
DEL/*[b]
007F/002A
Murray code (figure set, switched to with 0x1B)
_0 _1 _2 _3 _4 _5 _6 _7 _8 _9 _A _B _C _D _E _F
0_ NUL/SP
0000/0020
3
0033
COL
?
LS
000F
'
0027
8
0038
7
0037
LF
000A
²
00B2
4
0034
⁷⁄
2077 2044

002D/2212

215F
(
0028
⁹⁄
2079 2044
1_ 5
0035
.
002E
/
002F
2
0032
⁵⁄
2075 2044
6
0036
0
0030
1
0031
9
0039
?
003F
³⁄
00B3 2044
FS
000E
,
002C
£
00A3
)
0029
DEL/*[b]
007F/002A

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
0_ NUL
0000
E
0045
LF
000A
A
0041
SP
0020
S
0053
I
0049
U
0055
CR
000D
D
0044
R
0052
J
004A
N
004E
F
0046
C
0043
K
004B
1_ T
0054
Z
005A
L
004C
W
0057
H
0048
Y
0059
P
0050
Q
0051
O
004F
B
0042
G
0047
FS
000E
M
004D
X
0058
V
0056
LS/DEL
000F/007F
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
0_ NUL
0000
3
0033
LF
000A

002D/2212
SP
0020
BEL
0007
8
0038
7
0037
CR
000D
$
0024
4
0034
'
0027
,
002C
!
0021
:
003B
(
0028
1_ 5
0035
"
0022
)
0029
2
0032
#
0023
6
0036
0
0030
1
0031
9
0039
?
003F
&
0026
FS
000E
.
002E
/
002F
;
003B
LS
000F
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
0_ NUL
0000
3
0033
LF
000A

002D/2212
SP
0020
'
0027
8
0038
7
0037
CR
000D
ENQ
0005
4
0034
BEL
0007
,
002C
!
0021
:
003B
(
0028
1_ 5
0035
+
002B
)
0029
2
0032
£
00A3
6
0036
0
0030
1
0031
9
0039
?
003F
&
0026
FS
000E
.
002E
/
002F
=
003D
LS
000F

  Letter   Number   Punctuation   Symbol   Other   undefined

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).

Ita2
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.[24] 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

Footnotes

  1. ^ a b c d "At the disposal of each administration for its internal service"[23]
  2. ^ a b "[G]ives invisible correction on page printers & * on slip printers."[23]

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. ^ Bacon's Bilateral Cipher (PDF), retrieved 15 April 2012
  3. ^ "Jean-Maurice- Emile Baudot. Système de télégraphie rapide, June 1874. Brevet 103,898; Source: Archives Institut National de la Propriété Industrielle (INPI)".
  4. ^ H. A. Emmons (1 May 1916). "Printer Systems". Wire & Radio Communications. 34: 209.
  5. ^ William V. Vansize (25 January 1901). "A New Page-Printing Telegraph". Transactions. American Institute of Electrical Engineers. 18: 22.
  6. ^ "Gauss-Weber-Telegraph". Metrology Mile (in German). Measurement Valley. Retrieved 3 May 2009.
  7. ^ Pickover, Clifford A. (2009). The Math Book: From Pythagoras to the 57th Dimension, 250 Milestones in the History of Mathematics. Sterling Publishing Company. p. 392.
  8. ^ Procès d'Amiens Baudot vs Mimault
  9. ^ a b Jennings 2004
  10. ^ Beauchamp, K.G. (2001). History of Telegraphy: Its Technology and Application. Institution of Engineering and Technology. pp. 394–395. ISBN 0-85296-792-6.
  11. ^ Alan G. Hobbs, 5 Unit Codes, section Baudot Multiplex System
  12. ^ Gleick, James (2011). The Information: A History, a Theory, a Flood. London: Fourth Estate. p. 203. ISBN 978-0-00-742311-8.
  13. ^ Foster, Maximilian (August 1901). "A Successful Printing Telegraph". The World's Work: A History of Our Time. II: 1195–1199. Retrieved 9 July 2009.
  14. ^ Copeland 2006, p. 38
  15. ^ 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.
  16. ^ "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.
  17. ^ Smith, Gil (2001). "Teletype Communication Codes" (PDF). Baudot.net. Archived (PDF) from the original on 20 August 2008. Retrieved 11 July 2008.
  18. ^ 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). 3 (3 ed.). Berlin, Germany: Springer Verlag. pp. 328–329. ISBN 3-540-06242-4. LCCN 73-80607.
  19. ^ dataIP Limited. "The "Baudot" Code". Retrieved 16 July 2017
  20. ^ ITU-T Recommendation S.2 / 11/1988, published in Fascicle VII.1 of the Blue Book
  21. ^ "Enhanced Broadcast Solution – Interface Specification Final Version" (PDF). Deutsche Börse. 17 May 2010. Retrieved 10 August 2011.
  22. ^ Gillam, Richard (2002). Unicode Demystified:. Addison-Wesley. p. 30. ISBN 0-201-70052-2. Enhanced Broadcast Solution – Interface Specification Final Version
  23. ^ a b c d e f g h i j "Five-unit codes". NADCOMM museum. Archived from the original on 4 November 1999.
  24. ^ Jennings, Tom (20 April 2016). "An annotated history of some character codes: ITA2". Retrieved 20 January 2018. […] 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!

Further reading

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

Asynchronous serial communication

Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contains synchronization information in form of start and stop signals, before and after each unit of transmission, respectively. The start signal prepares the receiver for arrival of data and the stop signal resets its state to enable triggering of a new sequence.

A common kind of start-stop transmission is ASCII over RS-232, for example for use in teletypewriter operation.

Baud

In telecommunication and electronics, baud (; symbol: Bd) is a common measure of symbol rate, one of the components that determine the speed of communication over a data channel.

It is the unit for symbol rate or modulation rate in symbols per second or pulses per second. It is the number of distinct symbol changes (signaling events) made to the transmission medium per second in a digitally modulated signal or a bd rate line code.

Baud is related to, but not equivalent to, gross bit rate, which can be expressed as bits per second. If there are only two symbols in the system (typically 0 and 1), then baud and bits per second (bps) are equivalent.

Baudot

Baudot may refer to:

People:

Marc Antoine Baudot (1765-1837), deputy during the French Revolution

Émile Baudot (1845-1903), French telegraph engineer, inventor of the Baudot code

Anatole de Baudot (1834-1915), French architectTechnology:

Baudot code, a way to encode characters for sending over a communication channel

Bell character

A bell code (sometimes bell character) is a device control code originally sent to ring a small electromechanical bell on tickers and other teleprinters and teletypewriters to alert operators at the other end of the line, often of an incoming message. Though tickers punched the bell codes into their tapes, printers generally do not print a character when the bell code is received. Bell codes are usually represented by the label "BEL". They have been used since 1870 (initially in Baudot code).To maintain backward compatibility, video display terminals (VDTs) that replaced teletypewriters included speakers or buzzers to perform the same function, as did the personal computers that followed. Modern terminal emulators often integrate the warnings to the desktop environment (e.g., the Mac OS X Terminal will play the system warning sound) and also often offer a silent visual bell feature that flashes the terminal window briefly.

Donald Murray (inventor)

Donald Murray (1865–1945) was an electrical engineer and the inventor of a telegraphic typewriter system using an extended Baudot code that was a direct ancestor of the teleprinter (teletype machine). He can justifiably be called the "Father of the remote Typewriter".Murray's system became the International Telegraph Alphabet No. 2 (ITA2) or Murray Code; it was supplanted by the American Standard Code for Information Interchange (ASCII) in 1963.

Figure space

A figure space is a typographic unit equal to the size of a single typographic figure (numeral or letter), minus leading. Its size can fluctuate somewhat depending on which font is being used. This is the preferred space to use in numbers. It has the same width as a digit and keeps the number together for the purpose of line breaking.

Packet radio

Packet radio is a form of packet switching technology used to transmit digital data via wireless communications. Packet radio uses the same concepts of data transmission using datagrams that are fundamental to communications on the Internet, as opposed to older techniques used by dedicated or switched circuits. Packet radio can be used over long distances without the need for a physical connection between stations. Packet radio can also be used for mobile communications.

Packet radio is a digital radio communications mode. Earlier digital modes were telegraphy (using Morse code), teleprinter (using Baudot code) and facsimile.

Telecommunications device for the deaf

A telecommunications device for the deaf (TDD) is a teleprinter, an electronic device for text communication over a telephone line, that is designed for use by persons with hearing or speech difficulties. Other names for the device include teletypewriter (TTY), textphone (common in Europe), and minicom (United Kingdom).

The typical TDD is a device about the size of a typewriter or laptop computer with a QWERTY keyboard and small screen that uses an LED, LCD, or VFD screen to display typed text electronically. In addition, TDDs commonly have a small spool of paper on which text is also printed – old versions of the device had only a printer and no screen. The text is transmitted live, via a telephone line, to a compatible device, i.e. one that uses a similar communication protocol.

Special telephone services have been developed to carry the TDD functionality even further. In certain countries there are systems in place so that a deaf person can communicate with a hearing person on an ordinary voice phone using a human relay operator. There are also "carry-over" services, enabling people who can hear but cannot speak ("hearing carry-over," a.k.a. "HCO"), or people who cannot hear but are able to speak ("voice carry-over," a.k.a. "VCO") to use the telephone.

The term TDD is sometimes discouraged because people who are deaf are increasingly using mainstream devices and technologies to carry out most of their communication. The devices described here were developed for use on the partially-analog Public Switched Telephone Network (PSTN). They do not work well on the new internet protocol (IP) networks. Thus as society increasingly moves toward IP based telecommunication, the telecommunication devices used by people who are deaf will not be TDDs. In the US for example, the use of the term TDD is discouraged to avoid confusion with these partly-analog devices being referred to as TTYs.

Teletype Corporation, of Skokie, Illinois, made page printers for text, notably for news wire services and telegrams, but these used standards different from those for deaf communication, and although in quite widespread use, were technically incompatible. Furthermore, these were sometimes referred to by the "TTY" initialism, short for "Teletype". When computers had keyboard input mechanisms and page printer output, before CRT terminals came into use, Teletypes were the most widely used devices. They were called "console typewriters". (Telex used similar equipment, but was a separate international communication network.)

Telegraph code

A telegraph code is one of the character encodings used to transmit information through telegraphy machines. The most famous such code is Morse code.

Telegraphy

Telegraphy is the long-distance transmission of textual messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas pigeon post is not. Ancient signalling systems, although sometimes quite extensive and sophisticated as in China, were generally not capable of transmitting arbitrary text messages. Possible messages were fixed and predetermined and such systems are thus not true telegraphs.

The earliest true telegraph put into widespread use was the optical telegraph of Claude Chappe, invented in the late eighteenth century. The system was extensively used in France, and European countries controlled by France, during the Napoleonic era. The electric telegraph started to replace the optical telegraph in the mid-nineteenth century. It was first taken up in Britain in the form of the Cooke and Wheatstone telegraph, initally used mostly as an aid to railway signalling. This was quickly followed by a different system developed in the United States by Samuel Morse. The electric telegraph was slower to develop in France due to the established optical telegraph system, but an electrical telegraph was put into use with a code compatible with the Chappe optical telegraph. The Morse system was adopted as the international standard in 1865, using a modified Morse code developed in Germany.

The heliograph is a telegraph system using reflected sunlight for signalling. It was mainly used in areas where the electrical telegraph had not been established and generally uses the same code. The most extensive heliograph network established was in Arizona and New Mexico during the Apache Wars. The heliograph was standard military equipment as late as World War II. Wireless telegraphy developed in the early twentieth century. Wireless telegraphy became important for maritime use, and was a competitor to electrical telegraphy using submarine telegraph cables in international communications.

Telegrams became a popular means of sending messages once telegraph prices had fallen sufficiently. Traffic was became high enough to spur the development of automated systems – teleprinters and punched tape transmission. These systems led to new telegraph codes, starting with the Baudot code. However, telegrams were never able to compete with the letter post on price, and competition from the telephone, which removed their speed advantage, drove the telegraph into decline from 1920 onwards. The few remaining telegraph applications were largely taken over by alternatives on the internet towards the end of the twentieth century.

Teletype Model 33

The Teletype Model 33 is an electromechanical teleprinter designed for light-duty office. It is less rugged and less expensive than earlier Teletype machines. The Teletype Corporation introduced the Model 33 as a commercial product in 1963 after being originally designed for the US Navy. There are three versions of the Model 33:

the Model 33 ASR, (Automatic Send and Receive), which has a built-in 8-level punched tape reader and tape punch;

the Model 33 KSR (Keyboard Send and Receive), which lacks the paper tape reader and punch;

the Model 33 RO (Receive Only) which has neither a keyboard nor a reader/punch.The Model 33 was one of the first products to employ the newly standardized ASCII code. A companion Model 32 used the more established five-level Baudot code. Because of its low price and ASCII-compatibility, the Model 33 was widely used with early minicomputers.

X

X (named ex , plural exes) is the 24th and antepenultimate letter in the modern English alphabet and the ISO basic Latin alphabet.

Émile Baudot

Jean-Maurice-Émile Baudot (French: [emil bodo]; 11 September 1845 – 28 March 1903), French telegraph engineer and inventor of the first means of digital communication Baudot code, was one of the pioneers of telecommunications. He invented a multiplexed printing telegraph system that used his code and allowed multiple transmissions over a single line. The baud unit was named after him.

Baudot code (Continental and UK versions)
Baudot code (Continental and UK versions)
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; The sort keys present the table in the order: alphabetical, Gray and UK
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 £
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.
International telegraphy alphabet No. 2 (Baudot–Murray code)[19]
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
Early telecommunications
ISO/IEC 8859
Bibliographic use
National standards
EUC
ISO/IEC 2022
MacOS code pages("scripts")
DOS code pages
IBM AIX code pages
IBM Apple MacIntoshemulations
IBM Adobe emulations
IBM DEC emulations
IBM HP emulations
Windows code pages
EBCDIC code pages
Platform specific
Unicode / ISO/IEC 10646
TeX typesetting system
Miscellaneous code pages
Related topics

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