Emile Baudot
and the
First Data Communications


EMILE BAUDOT

Jean Maurice Emile Baudot (1845-1903) was a French engineer who invented the first digital Telecommunications code and hardware. Working for the French Telecommunications Service, he invented the code in 1870. By 1874 or 1875 (various sources give both dates) he had also perfected the electro-mechanical hardware to send his code. In addition, his system allowed up to six operators to send messages on the same communications line. Therefore, it was the first practical use of multiplexing in telecommunications as well. The legacy of Baudot's work is alive today.


THE CODE

The Baudot Code is the first truly digital one. It consists of only two states, both logically and electrically. Logically, the only states are "1" and "0" . Today we call the unit that can have these two logical states a "bit". Electrically, the states are current flowing(or "1"), and no current flowing (or "0").

Each character consists of 5 bits. Two logical states and five bits allows 32 characters. (2^5 = 32). Baudot needed 26 characters for the alphabet, 10 for numbers, and more for miscellaneous characters. In order to have 36 + characters, he used two special characters, LTRS and FIGS, to give a total of 64 possibilities. LTRS (11111) precedes Alphabetic characters. FIGS (11011) precedes numerical and special characters such as punctuation.

This short code example shows how this works. The message is "A3". The code must say that the first character is a letter, and that the second is a number.
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THE HARDWARE

The hardware had three main parts. They were the keyboard, the distributor, and a tape. The keyboard, seen at the left, had five piano like keys. A spacer separated the keys into one group of two and another of three. The operator entered the five bit code for each character at the keyboard. The keyboard input went to the distributor.

The distributor, pictured on the right, was the heart of the hardware system. Both the transmitter and the receiver used a distributor. On the transmitter end, a keyboard was connected to a set of metal brushes inside the distributor. The brushes, rotated by either weights or an electric motor, made and broke contact with stationary conductive elements called segments. Typically, each system had four to six keyboards, each connected to its own set of brushes and segments in the distributor. Each set connected to a single communications line. This was the first successful multiplexing system in electrical telecommunications.

In the receiver part of the distributor was a set of electro-magnets that stored the encoded messages. A punch mechanism transferred the stored information to a tape. The hole pattern on the tape reflected the two/three pattern of the keyboard.
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LEGACY
The legacy of Baudot's work continues to this day. Teletypes (TTY) and radio teletypes (RTTY) still use an expanded version of the Baudot code. His code is the direct forerunner of the present day ASCII code. In fact, the first ASCII code was simply a modified Baudot code. Modern information theory, developed by Claude Shannon, is based on digital data communications. Baudot, of course, invented digital data communications. And the enormous amount of traffic that modern telecommunications systems send would not be possible without mutiplexing.
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ACKNOWLEDGMENTS
Here are the Web sites I used to research this page. I hope you visit them and learn more about Baudot and the history of telecommunications. Enjoy!

Data Communications Milestones

A Brief History of Character Codes

8-Bit Character Sets - Historical Background

TELEGRAPHY

Part6: Baudot and ASCII Codes

A Short History of Telegraphy

From the Instruction Manual for BTL.exe
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