page_title: Telegraph code
section_title: Baudot code
hierarchical_section_title: Telegraph code / Automatic telegraph codes / Baudot code
caption_attribution_description: English: Baudot code as originally laid out in Baudot's patent
context_page_description: A telegraph code is one of the character encodings used to transmit information by telegraphy. Morse code is the most well known such code. Telegraphy usually refers to the electrical telegraph, but telegraph systems using the optical telegraph were in use before that. A code consists of a number of code points, each corresponding to a letter of the alphabet, a numeral, or some other character. In codes intended for machines rather than humans, code points for control characters, such as carriage return, are required to control the operation of the mechanism. Each code point is made up of a number of elements arranged in a unique way for that character. There are usually two types of element, but more element types were employed in some codes not intended for machines. For instance, American Morse code had about five elements, rather than the two of International Morse Code.
  Codes meant for human interpretation were designed so that the characters that occurred most often had the fewest elements in the corresponding code point. For instance, Morse code for E, the most common letter in English, is a single dot, whereas Q is ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄.
context_section_description: Early printing telegraphs continued to use Morse code, but the operator no longer sent the dots and dashes directly with a single key.  Instead they operated a piano keyboard with the characters to be sent marked on each key.  The machine generated the appropriate Morse code point from the key press.  An entirely new type of code was developed by Émile Baudot, patented in 1874.  The Baudot code was a 5-bit binary code, with the bits sent serially.  Having a fixed length code greatly simplified the machine design.  The operator entered the code from a small 5-key piano keyboard, each key corresponding to one bit of the code.  Like Morse, Baudot code was organised to minimise operator fatigue with the code points requiring fewest key presses assigned to the most common letters.
  Early printing telegraphs required mechanical synchronisation between the sending and receiving machine.  The Hughes printing telegraph of 1855 achieved this by sending a Morse dash every revolution of the machine.  A different solution was adopted in conjunction with the Baudot code.  Start and stop bits were added to each character on transmission, which allowed asynchronous serial communication.  This scheme of start and stop bits was followed on all the later major telegraph codes.
caption: The original Baudot code
exif: {}