This document by Tom Jennings describes a history of ASCII (the American Standard Code for Information Interchange) and its immediate ancestors including FIELDATA, ITA2, Murray’s telegraphy code, Baudot’s telegraphy code, and Morse’s telegraphy code. This history provides a thorough foundation for how ASCII came to be and serves as a basis for understanding electronic communication.
This research isn’t a detailed history of the development of character codes per se, but of the codes themselves and their specific meanings.