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The Baudot Code
Five Level Teletypewriter Code
Baudot Code (International Telegraph Alphabet 2 (ITA2) Version). Adopted in the 1930's.
Baudot Code. Invented by the Frenchman Emile Baudot in 1870.
BLK - Blank. No-action code. On paper tape, BLK only punches the traction hole.
SP - Space. The typing assembly advances one column to the right.
CR - Carriage Return. The typing assembly positions to the left-most column.
LF - Line Feed. The platen advances the paper by one line.
BELL - The alert bell rings.
LTRS - Letters. The typing assembly moves to the unshifted position, and subsequent characters that are printed will come from the "Letters" section of the Baudot code.
FIGS - Figures. The typing assembly moves to the shifted position, and subsequent characters that are printed will come from the "Figures" section of the Baudot code.
The Baudot Code has been used extensively in telegraph systems. It is a five bit code invented by the Frenchman Emile Baudot in 1870. Using five bits allowed 32 different characters. To accomodate all the letters of the alphabet and numerals, two of the 32 combinations were used to select alternate character sets. The figures column is valid after a figures shift character has been received. It remains in effect until a letters shift is received, after which the letters column should be referred to (and vice-versa).
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 TDDs and some ham radio applications, such as Radio Teletype (RTTY).
The original, true, baudot code differs from Murray's code. Murray's code was developed from Baudot's code. Baudot's code was replaced by Murray's code in 1901. And ITA2 replaced both by the early 1930's, so virtually all "teletype" equipment made in the U.S. uses ITA2 or the U.S. national version of the code.
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 signals that the following code is to be interpreted as being in the FIGS set, until this is reset by the LTRS character.
The five-bit words are bracketed by a start bit (space) and a stop bit (mark). Idling is shown by the 'marking' state.
There were a few variations in character codes for five-level teletypewriter machines. The two most-common character codes were ITA2 and USTTY (a variation of ITA2).
The USTTY and ITA2 5-level teletypewriter codes are commonly referred to as "Baudot" codes. While this is technically incorrect, these popular 5-level codes evolved from the work of Jean Maurice Emile Baudot of France -- it seems fitting to accept the defacto reference to "Baudot" as implying USTTY or ITA2 codes, since they were the 5-level codes that saw practical use in teletypewriter systems. However, the true Baudot code dates to around 1874, when Baudot designed the "Baudot Multiplex System," a printing telegraph. The system used a 5-level code generated by a device with five keys, operated with two left-hand fingers, and three right-hand fingers -- this required great skill on the part of the operator who entered the code directly.
However, it was still a major improvement in communications -- prior to Baudot's design, communication was carried out using Morse code with a telegraph key. The 5-level "Baudot" code was actually designed by Johann Gauss and Wilhelm Weber. Used primarily in France, the Baudot Multiplex System, also made inroads in Britain. The original Baudot code defined the familiar structure of a 5-level code set, using LTRS and FIGS case shifting, and became known as the International Telegraph Alphabet 1 (ITA1). Another recognition of Baudot's contribution to data communications is the term "baud," which refers to bits-per-second speed of serial data.
Around 1901, Donald Murray of New Zealand developed an automatic telegraphy system, using a typewriter-like keyboard mechanism, and a variation on the original Baudot 5-level code. While Baudot's code was designed with finger-actuation in mind, Murray's code was designed for mechanization, to minimize machine wear for frequently-occuring characters. The Murray system employed a keyboard perforator, which allowed an operator to manually 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. Early British Creed machines were used with the Murray system.
Around 1930, the CCITT (International Telegraph and Telephone Consultative Committee) introduced the International Telegraph Alphabet 2 (ITA2). The United States standardized on a variation of ITA2 called the American Teletypewriter code or USTTY. ITA2 and the USTTY variant became the basis for 5-level teletypewriter codes until 7-level ASCII code debuted (in an upper-case-only form) in 1963, and finally matured in 1967 to the form still used today.
Common to all of these 5-level codes is the shifting of keys using a FIGS or LTRS code. The same 5-level (5-bit) code is used to represent a lowercase symbol (LTRS case) or an uppercase symbol (FIGS case). When the LTRS or FIGS character is transmitted, it defines whether subsequent characters are to be interpreted as lowercase or uppercase. The receiving machine must remember the case until it is next changed.
Communicators were most familiar with the use of the Baudot Code on the perforated paper tape that was prepared with message traffic. While some later models of teletype equipment (reperforators or reperfs) printed the characters on the paper tape, Communicators were capable of "reading" an unprinted plain tape and aligning it on the TD (Transmitter Distributor). This was commonly referred to as "reading tape".
Wallet Card
Source: http://www.rtty.com/
Wallet Card
Source: http://www.rtty.com/
Pocket Ruler
Source: http://www.rtty.com/
Model 28 KSR Model 28 KSR & ASR
Model 28 ASR-2A
Photo provided by: CTOC/LCDR Peter J. Christensen, Retired
[ I think it's the one he keeps in his basement ;- ) ]
Paper Tape Punch
Commonly referred to as a "Puka Punch".
When used to punch a hole in a paper tape, it exactly
matched the size and shape of a hole made by a TTY perforator.
For example: communicators could turn a bad/stray character
into a "letters" function, by punching out all five levels of the
character, and thereby eliminate the bad or stray character.
Puka punches were originally used to punch holes in puka
shells, so they could be strung into bracelets and necklaces.
The legend goes (probably a myth) that a sailor stationed in Hawaii
discovered the puka punch and distributed them to fellow communicators.
Photo provided by: CTO1 Hugh H. Rea, Retired.
