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In digital telegraphy (teletype, telex) a standard 5-bit code is commonly
used to represent a character (letter, number or punctuation mark).
This is often called the Baudot code, although this name is
actually wrong. The official name for the latest telegraphy standard
is ITA2 (International Telegraph Alphabet No 2). It has been in use
until it was replaced by ASCII in 1963.
The most common Baudot code is also known as the Murray code.
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The ITA2 Standard (CCITT-2)
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Normal text consists of over 50 different characters (26 letters,
10 numbers, 10 punctuation marks and some control codes).
In the ITA2 standard, 5 bits are used to represent a character, which
means that we can create only 32 different codes (25).
As this would not be sufficient to create normal text, most codes
are used twice (i.e. have two different meanings) and special codes
are used to 'shift' between the two code sets (letters and figures, or
LTRS and FIGS).
The table below shows the interpretation of the commonly used ITA2
standard. Although this code has officially been superceeded by ASCII,
it is still in use on some old telex networks and by Radio Amateurs.
Some of the cipher machines described on this website,
use 5-bit digital telegraphy and most of these use the ITA2 standard.
LTRS-shift is represented by 11111 (5 holes), so that it can be
used to wipe part of a paper tape, without affecting the rest.
Normally, a paper tape would start with two LTRS characters, to ensure
that the teletype is in Letter-mode.
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Ltr
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Letters (A-Z)
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Fig
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Figures (Numbers and punctuation marks)
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Ctrl
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Control characters
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Hex
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Hexadecimal code
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Bin
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Binary, Positions of the holes in the paper tape
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#
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Ltr
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Fig
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Hex
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Bin
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Description
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0
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NUL
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00
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00000
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NULL, Nothing (blank tape)
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1
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E
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3
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01
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10000
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2
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LF
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02
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01000
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Line Feed (new line)
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3
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A
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-
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03
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11000
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4
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SP
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04
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00100
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Space
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5
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S
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'
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05
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10100
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6
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I
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8
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06
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01100
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7
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U
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7
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07
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11100
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8
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CR
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08
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00010
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Cariage Return
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9
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D
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ENC
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09
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10010
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Enquiry (Who are you?, WRU)
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10
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R
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4
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0A
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01010
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11
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J
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BEL
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0B
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11010
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BELL (ring bell at the other end)
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12
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N
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,
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0C
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00110
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13
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F
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!
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0D
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10110
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14
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C
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:
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0E
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01110
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15
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K
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(
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0F
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11110
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16
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T
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5
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10
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00001
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17
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Z
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+
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11
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10001
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18
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L
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)
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12
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01001
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19
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W
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2
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13
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11001
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20
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H
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$
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14
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00101
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Currency symbol (can also be £)
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21
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Y
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6
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15
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10101
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22
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P
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0
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16
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01101
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23
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Q
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1
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17
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11101
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24
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O
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9
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18
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00011
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25
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B
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?
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19
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10011
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26
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G
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&
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1A
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01011
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27
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FIGS
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1B
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11011
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Figures (Shift on)
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28
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M
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.
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1C
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00111
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29
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X
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/
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1D
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10111
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30
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V
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;
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1E
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01111
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31
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LTRS
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1F
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11111
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Letters (Shift off)
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Cipher machines that use ITA2
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Sunday, 23 June 2013 - 15:52 CET
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