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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.

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 (ITA2). ITA2 is still used in TDDss and some ham radio applications, such as RTTY.

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 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 ENQ(1) 00001 01 E 3 01101 0D F ! (2) 11010 1A G & (2) 10100 14 H (2) 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..]

(1) "ENQuiry" will trigger the other machine's answerback. It means "Who are you?"

(2) Not used in telex communication.

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.

US American implementations of Baudot code may differ in the use of ENQ, +, and f,g,h on the FIGS layer. The above table represents the official ITA2 code.

External references:


Adapted from FOLDOC, with permission.