A five-bit data coding scheme invented by Emile Baudot in the 1870s for use in the Baudot Distributor, a sort of automatic telegraph that supported higher speed transmission over a circuit between two synchronized electromechanical devices.The Baudot Distributor soon gave way to the teletype (TTY), which also employed the Baudot coding scheme, subsequently known as International Telegraph Alphabet #2 (ITA #2). Updated in 1930, Baudot is limited to 32 (2 5 ) characters. Considering that each bit has two possible states (1 or 0), 5 bits in sequence yield 2 5 (32) possible combinations. Because 32 values is not sufficient to represent all 26 characters in the English alphabet, plus the 10 decimal digits, necessary punctuation marks and the space character, the shift key operates to shift between letters and other characters. Baudot employs asynchronous transmission, with start and stop bits separating characters.Telephone Devices for the Deaf (TDDs) and telex machines still use ITA #2. See also asynchronous transmission, code set, TDD, telegraph, telex, and TTY.