case sel is
when “000” => y<= data(0);
when “001” => y<= data(1);
when “010” => y<= data(2);
when “011” => y<= data(3);
1) when others => y<= ‘0’;
2) when others => y<= ‘Z’;
3) when others => y<= ‘X’;
4) when others => NULL;
end case;
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjgskJ3P3BD2-0GDrn0VtUVKan2dTmQ3ZP8gm237LVZyP9jwC5YDn8aMgeL09H_rgC108pw_IyqxzUl0Jqc4oi8tFyoZNMKgp_J7fDWPGfp1p9tnOOVTniBs_3RjgUikVGI4mEhmsH3K4IY/s320/dia+1.png)
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgYN5ify5OIZ49rlmkKhKA3SXTabNVYUtimKpe9HGt_PE0zesYju7A3hncJEVWUzvY9jpLrWfSi4c6gnwZeCefzcbKblHdUEfmVnPE5zUvvQuRdaxS_pjQMFn-iT8x_DAgfwIAdEC73XjDD/s320/dia+2.png)
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