CHR and ASCII are opposites.
ASCII (character) returns the binary equivalent of the character passed into the function.
SQL>
SQL> declare
2 v_nr number;
3 v_tx char(1);
4 begin
5 v_nr:=ascii('A');
6 DBMS_OUTPUT.put_line(v_nr);
7 v_tx:=chr(v_nr);
8 DBMS_OUTPUT.put_line(v_tx);
9 end;
10 /
65
A
PL/SQL procedure successfully completed.
SQL>