2015/10/28 2+2=4位元多工器

module top;

wire [3:0]A,SEL,B,OUT;

system_clock #100 clock1(A[1]);
system_clock #200 clock2(A[0]);
system_clock #6400 clock3(SEL);
system_clock #400 clock4(B[1]);
system_clock #800 clock5(B[0]);
system_clock #1600 clock6(A[2]);
system_clock #3200 clock7(B[2]);
system_clock #800 clock8(A[3]);
system_clock #6400 clock9(B[3]);
mux2 M32(OUT[3:2], A[3:2], B[3:2], SEL);

mux2 M10(OUT[1:0], A[1:0], B[1:0], SEL);

endmodule


module mux2(OUT, A, B, SEL);
output [1:0] OUT;
input [1:0] A,B;
input SEL;
mux hi (OUT[1], A[1], B[1], SEL);
mux lo (OUT[0], A[0], B[0], SEL);
endmodule


module mux(OUT, A, B, SEL);

output OUT;

input A,B,SEL;

not I5 (sel_n, SEL) ;

and I6 (sel_a, A, SEL);

and I7 (sel_b, sel_n, B);

or I4 (OUT, sel_a, sel_b);

endmodule



module system_clock(clk);
parameter PERIOD=100;
output clk;
reg clk;

initial clk=0;

always
 begin
#(PERIOD/2) clk=~clk;
 end

always@(posedge clk)
 if($time>12800)$stop;

endmodule