Baudot Code

In the dawn of time (about 1875 A.D.), a Frenchman named Emile Baudot devised a way to connect two typing machines so that whatever was typed on one would be typed on the other automatically. 

The machines, some of which are still used today, are called teletypes.  Teletype machines were used for data communications before computers were built, and were used as data terminals on computers until replaced by video display terminals (which have since been replaced by personal computers running programs which emulate teletype machines or video display terminals.)

Baudot code has several limitations which make it less than ideal for modern use. 

The technology of the time imposed a 5 level (5 bit) limit to the code.  This allows only 32 characters, normally not adequate for even the basic alphabet and digits.  Baudot code extends the character set to 55 characters by using two codes, LTRS and FIGS, as shift controls.  Each shift code determines the meaning of the codes which follow it.  For example, the sequence 11111 00011 01010 00001 means "ARE", while the sequence 11011 00011 01010 00001 means "-43".

There are no lower case letters in the Baudot code.  There are only the 26 capitol letters, the 10 digits, three format control characters (space, LF, and CR), 15 punctuation marks, and an audible signal (Bell).  There are actually several different versions of the Baudot code, with different meanings for the punctuation marks.

The codes are also not in any obvious order.  This did not matter at the time the code was devised, but doing a computer sort on the Baudot code does not put items into alphabetic order. 

The Baudot code was used for years for sending telegrams, and is mainly used today for TTY communications by the deaf. 

Baudot code is typically transmitted using an asynchronous serial protocol.  The least significant bit (LSB) is sent first, and the most significant bit (MSB) is sent last. 

Code Character LTRS FIGS 00000 Blank 00001 E 3 00010 LF 00011 A - 00100 Space 00101 S BELL 00110 I 8 00111 U 7 Code Character LTRS FIGS 01000 CR 01001 D $ 01010 R 4 01011 J ' 01100 N , 01101 F ! 01110 C : 01111 K ( Code Character LTRS FIGS 10000 T 5 10001 Z " 10010 L ) 10011 W 2 10100 H # 10101 Y 6 10110 P 0 10111 Q 1 Code Character LTRS FIGS 11000 O 9 11001 B ? 11010 G & 11011 FIGS 11100 M . 11101 X / 11110 V ; 11111 LTRS