From "A Brief History of Character Codes" by Steven J. Searle

...The next great leap in telegraph technology was a primitive printing
telegraph, or "teleprinter," patented by Jean-Maurice-Émile Baudot
(1845-1903) in France in 1874. Like Morse's telegraph, it involved the
creation of a new character code, the 5-bit Baudot code, which was also
the world's first binary character code for processing textual data.
Messages encoded in Baudot's code were printed out on narrow two-channel
transmission tapes by operators who created them using a special five-key
keypad, although in later versions typewriter keyboards that automatically
generated the proper five-unit sequences were employed. Another
interesting feature of Baudot's teleprinter system was that it was a
"multiplex" system that allowed up to six operators to share a single
telegraph line using a time division system. This led to a considerable
increase in the transmission capacity of a telegraph line. Baudot's system
proved to be fairly successful, and it remained in widespread use in the
20th century until it was displaced by the telephone, and, of course,
personal computer communications.

Being a 5-bit character code, Baudot code only has room for handling 32
elements (2^5 = 32 code points). This is not enough to handle both the
letters of the Latin alphabet plus Arabic numerals and punctuation marks,
so Baudot code employs a "locking shift scheme" to switch between two
planes of 32 elements each (Fig. 3), which can be compared to the shifting
and locking into place the upper case letters on a mechanical typewriter.
Like the subset of International Morse Code given above, Baudot code has
codes for the upper case letters of the Latin alphabet, Arabic numerals,
and punctuation marks. However, in addition, it has control codes, which
are also a feature of the character codes used in today's personal
computers. The two binary elements of Baudot were represented as either a
mark or a space on the transmission tape; they were translated into a
electrical current "on" and electric current "off" during transmission.
Each character of a message being sent was preceded by a stop bit, and
followed by a stop bit, which made it slow by today's standards.

The reason Baudot was forced to limit his character code to 5 bits--and
hence leave out the lower case Latin letters--was because of hardware
constraints. A more complex code--even just a 6-bit code--would have
necessitated a much more complex electromechanical device to transmit it,
which would have been extremely difficult to fabricate using the
technology in Baudot's time. After modifying Baudot's code to 55
elements--thus allowing for three places for national variants--the CCITT
(Comité Consultatif International Télégraphique et Téléphonique
[Consultative Committee on International Telephone and Telegraph]) in
Geneva, Switzerland, standardized it in 1932 as a 5-bit code for
teleprinters. It was given the designation "International Telegraphic
Alphabet No. 2." In the field of telegraphy, Baudot also left a portion of
him name to posterity in the form of the "Baud rate," which refers to the
number of data signalling events that occur in a second.