CONVERT
CONVERT(x,to_char_set[,from_char_set]) converts x from from_char_set to to_char_set.
SQL>
SQL> select convert('A ', 'US7ASCII') from dual;
CONV
----
A Z
SQL> select convert('A ', 'US7ASCII', 'WE8ISO8859P1') from dual;
CONV
----
A ?
SQL>