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ITA2 code
Baudot-Murray code

In digital telegraphy (teleprinter, telex) a standard 5-bit code is commonly used to represent a character (letter, number or punctuation mark). Although this code is generally known as the Baudot code, this name is actually wrong. The official name for the latest telegraphy standard is ITA2 (International Telegraph Alphabet No 2). It was superceeded by ASCII in 1963, but is still used by amateurs today. The most common 'Baudot' code is also known as Murray code, or as Baudot-Murray code. The ITA2 standard is used widely with historical cipher machines.
 
ITA2 Standard   CCITT-2
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 known as Letters (LTRS) and Figures (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 many of these (if they support the Latin character set) follow the ITA2 standard.


LTRS-shift is represented by 111·11 (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 Letters-mode. By convention, the holes (bits) in the tape are called channels or tracks and the tape is shown as it would run through the reader away from you.
 
Ltr Letters (A-Z)
Fig Figures (Numbers and punctuation marks)
Ctrl Control characters
Hex Hexadecimal code
Bin 1 Binary, Positions of the holes in the paper tape

 
# Ltr Fig Hex Bin  
0 NUL 00 000·00 NULL, Nothing (blank tape)
1 E 3 01 000·01  
2 LF 02 000·10 Line Feed (new line)
3 A - 03 000·11  
4 SP 04 001·00 Space
5 S ' 05 001·01  
6 I 8 06 001·10  
7 U 7 07 001·11  
8 CR 08 010·00 Cariage Return
9 D ENC 09 010·01 Enquiry (Who are you?, WRU)
10 R 4 0A 010·10  
11 J BEL 0B 010·11 BELL (ring bell at the other end)
12 N , 0C 011·00  
13 F ! 0D 011·01  
14 C : 0E 011·10  
15 K ( 0F 011·11  
16 T 5 10 100·00  
17 Z + 11 100·01  
18 L ) 12 100·10  
19 W 2 13 100·11  
20 H $ 14 101·00 Currency symbol (can also be £)
21 Y 6 15 101·01  
22 P 0 16 101·10  
23 Q 1 17 101·11  
24 O 9 18 110·00  
25 B ? 19 110·01  
26 G & 1A 110·10 Can also be @ 
27 FIGS 1B 110·11 Figures (Shift on)
28 M . 1C 111·00  
29 X / 1D 111·01  
30 V ; 1E 111·10  
31 LTRS 1F 11·111 Letters (Shift off)

 
Cipher machines that use ITA2

Other standards

References
  1. ECMA, Standard ECMA-10 for Data Interchange on Punched Tape
    2nd Edition. July 1970.

  2. Wikipedia, Punched tape
    Retrieved January 2015.

Further information

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Crypto Museum. Last changed: Friday, 29 May 2015 - 13:18 CET.
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