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The Baudot character code system is a method of transmitting basic text messages containing the Roman alphabet and numerals, along with a limited set of symbols. The coding system was originally devised in 1870 by Emil Baudot, and consists of 32 code combinations that allowed messages to be communicated between two locations by means of a six wire electrical circuit.

Because 32 is not enough combinations to communicate all letters and numbers, two codes of the 32 are used to "shift" or select which character set is to be used for conveying subsequent characters. The earliest Baudot devices were essentially modified typewriters, so the two shift codes performed the same function as setting or releasing the SHIFT LOCK key on a standard typewriter keyboard, mechanically selecting the top or bottom set of characters on the print hammers that would be used from that point on.

The Baudot character code was also used in the early "5-level" two-wire and radio-based "Teleprinters" that appeared early in the 20th century. These devices used Baudot code within the sending and receiving device, and transmitted the five signals in serial, one pulse (or bit) at a time, with a fixed timing. A receiving device would receive the serial stream of pulses (or bits) and would perform the electrical or mechanical equivalent of separating the five signals so that the original character could be printed or some other action performed.

Although the sending and receiving equipment was now more complex than earlier models, these devices were considered to be a great improvement because fewer wires had to be run between locations, making the system far more economical, and the messages could also be sent by radio. It also regulated the transmission speed, which prevented faster typists from jamming the print hammers in the receiving printer.

The introduction of the "5-level" teletypeprinter helped supercede Morse code, and Baudot became the primary communication method for Western Union and virtually all news wire services. It was also used widely by the military organizations of numerous countries. The Baudot system saw regular service until these devices started to be replaced with ASCII-based equipment in the mid to late 1960s.

Some widely-deployed devices that used the Baudot coding system were the TG-7 and TG-37 teletypewriters, used by the United States Army beginning in the 1940s. In particular, the United States Army used the TG-7-A, TG-7-B, and the TG-37-B models. The TG-37-B used a special "Weather" FIGS character set instead of the Western Union/Teletype character set shown below. (The weather symbol set included directional arrows and other symbols ideal for providing weather observation and prediction reports.)

Western Union/TeleTypewriters US Baudot Code Assignments

The following table shows the Baudot code assignments used on TeleType brand of equipment (TTYs) manufactured by Western Electric for United States use.

The background color for each code or symbol indicates the category that the code resides in. Red indicates control (non-printable) codes. Orange indicates basic punctuation and symbols. Yellow indicates numeric digits. Green indicates the uppercase letters.

CCITT/ITU Original Baudot Code Assignments

The following table shows the Baudot code assignments used on equipment compliant with the original coding modifications created by the CCITT/ITU.

The background color for each code or symbol indicates the category that the code resides in. Red indicates control (non-printable) codes. Orange indicates basic punctuation and symbols. Yellow indicates numeric digits. Green indicates the uppercase letters.

CCITT/ITU Baudot Code Second Edition Assignments

The following table shows the Baudot code assignments used on equipment compliant with the second edition of coding modifications created by the CCITT/ITU.

Essentially this code is the original CCITT/ITU assignments with three differences: Two codes previously undefined by the CCITT are adopted from the Western Union/US character set ("!" and "&"), and the third code that was previously undefined by the CCITT is assigned to the British Sterling Pound symbol. In Western Union/US models, this third code was either used for the "#" character, or for motor control, depending on printer model.

The background color for each code or symbol indicates the category that the code resides in. Red indicates control (non-printable) codes. Orange indicates basic punctuation and symbols. Yellow indicates numeric digits. Green indicates the uppercase letters.

Related Topics

Extended Binary Coded Decimal Information Code Reference (EBCDIC) (HTML)

SIXBIT Character Code Reference (HTML)

RADIX50 Character Code Reference (HTML)

Return to the Telecommunications Reference Index (HTML)

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