ASCII was defined 1968 and revised 1970 by ANSI (standard: ANSI X3.4-1977). ANSI X3.4-1977 only standardizes the first 7 bits. So, it could be used as basis for further international character sets.
See also
UTF-8 preservers the full range of the US-ASCII chracters.
In vim, the character that an ASCII value represents, is returned by nr2char.