process(sel)
begin
if sel=1 then
out_sel<=sel1;
elsif sel=2 then
out_sel<=sel2;
elsif sel=3 then
out_sel<=sel3;
elsif sel=4 then
out_sel<=sel4;
elsif sel=5 then
out_sel<=sel5;
elsif sel=6 then
out_sel<=sel6;
elsif sel=7 then
out_sel<=sel7;
else sel=8 then
out_sel<=sel8;
end if;
希望能帮到你!