4-bit 3 to 1 multiplexer with priority

4-bit 3 to 1 multiplexer with priority

//---------------------------------------
//4-bit 3 to 1 multiplexer with priority
//---------------------------------------
module MUX_3x1_Priority(y, sel, a, b, c);

input [2:0] sel;
input [3:0] a, b, c;
output reg [3:0] y;

always @ (sel or a or b or c)
 begin
  casez (sel)
   3'bzz1 : y=a;
   3'bz10 : y=b;
   3'b100 : y=c;
   default : y=4'bzzzz;
  endcase
 end
endmodule

// 時間單位 1ns, 時間精確度10 ps

`timescale 10ns/10ps 

module TB;

/*

module MUX_3x1_Priority(y, sel, a, b, c);

input [2:0] sel;

input [3:0] a, b, c;

output reg [3:0] y;

*/

// Inputs

    reg [2:0] sel;

    reg [3:0] a;

    reg [3:0] b;

    reg [3:0] c;

// Outputs

    wire [3:0] y;

// Instantiate the UUT

MUX_3x1_Priority UUT (.y(y), .sel(sel), .a(a), .b(b), .c(c));

 

// Montoring signals

initial $monitor($time, "y=%h, sel=%b, a=%h, b=%h, c=%h", y, sel, a, b, c);

// Initialize Inputs

initial begin

  sel = 3'b000;

  a = 4'b0000;

  b = 4'b1010;

  c = 4'b1111;

end  

always

  #10 sel = sel + 3'h1;

 initial #80 $finish; //Complete simulation after 160 units

endmodule