Some of the design decisions of ASCII are covered in the original standard (first link) and in the other references here:

American Standard Code for Information Interchange http://www.wps.com/projects/codes/X3.4-1963/index.html

Revised U.S.A. Standard Code for Information Interchange http://www.wps.com/J/codes/Revised-ASCII/index.html


Eric Fischer, The Evolution of Character Codes, 1874-1968 http://www.pobox.com/~enf/ascii/ascii.pdf

Tom Jennings, An annotated history of some character codes or ASCII: American Standard Code for Information Infiltration http://www.wps.com/J/codes/

R W Bemer, The 1960 Survey of Coded Character Sets: The Reasons for ASCII, http://www.trailing-edge.com/~bobbemer/SURVEY.HTM

R W Bemer, Design of an improved transmission/data processing code http://dx.doi.org/10.1145/366532.366538


Charles E. MacKenzie, Coded Character Sets: History and Development 978-0201144604