Baudot code

The Baudot code, named after its inventor Emile Baudot, is a character set predating EBCDIC and ASCII and used originally and primarily on teleprinters. Use of Baudot reportedly survives in TDDs and some HAM radio applications.

Baudot's original code is known as International Telegraph Alphabet No 1, and is no longer used.

Baudot code was then improved by Donald Murray[?] by adding extra characters and shift codes. This code is what is generally known as the 'Baudot code', also known as the International Telegraph Alphabet No 2 (IA2).

In Baudot, characters are expressed using five bits. Baudot uses two code sub-sets, the "letter shift" (LTRS), and the "figure shift" (FIGS). The FIGS character (11011) signals that the following code is to be interpreted as being in the FIGS set, until this is reset by the LTRS (11111) character.

 binary  hex    LTRS   FIGS
 - - - - - - - - - - - - - - -

  00011  03      A      -
  11001  19      B      ?
  01110  0E      C      :
  01001  09      D      $
  00001  01      E      3
  01101  0D      F      !
  11010  1A      G      &
  10100  14      H      #
  00110  06      I      8
  01011  0B      J      BELL
  01111  0F      K      (
  10010  12      L      )
  11100  1C      M      .
  01100  0C      N      ,
  11000  18      O      9
  10110  16      P      0
  10111  17      Q      1
  01010  0A      R      4
  00101  05      S      '
  10000  10      T      5
  00111  07      U      7
  11110  1E      V      ;
  10011  13      W      2
  11101  1D      X      /
  10101  15      Y      6
  10001  11      Z      "
  01000  08      CR     CR
  00010  02      LF     LF
  00100  04      SP     SP
  11111  1F      LTRS   LTRS

  11011  1B      FIGS   FIGS
  00000  00      [..unused..]

Where CR is carriage return, LF is linefeed, BELL is the bell, SP is space, and STOP is the stop character.

Note: these bit values are often shown in inverse order, depending (presumably) which side of the paper tape you were looking at.

Local implementations of Baudot code may differ in the use of #, STOP, BELL, and '.

External references:

• http://www.nadcomm.com/fiveunit/fiveunits.htm
• http://www.cwi.nl/~dik/english/codes/5tape#ccitt1
• http://www.cwi.nl/~dik/english/codes/5tape#ccitt2

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Adapted from FOLDOC, with permission.