subdesign  control1
(
opa1[3..0],opb1[3..0],opc1[3..0],opd1[3..0] :input;
opa2[3..0],opb2[3..0],opc2[3..0],opd2[3..0] :input;
con                                         :input;
outa[3..0],outb[3..0],outc[3..0],outd[3..0] :output;
)
begin
if con  then
outa[]=opa2[];
outb[]=opb2[];
outc[]=opc2[];
outd[]=opd2[];
else 
outa[]=opa1[];
outb[]=opb1[];
outc[]=opc1[];
outd[]=opd1[];
end if;
end;