`timescale 1ns / 1ps

module gen_clock();

    reg clk;
    
    initial begin
        clk = 1'b0;
    end
    
    always begin
        #5 clk = ~clk; // Period to be determined
    end

endmodule

module mux(input wire [1:0] switch,
           input wire [8:0] A,B,C,D,
           output reg [8:0] out);
           
    always @(A,B,C,D,switch) begin
        case (switch)
            2'b00 : out = A;
            2'b01 : out = B;
            2'b10 : out = C;
            default: out = D;
        endcase
    end
endmodule

module register(input wire clk, reset,
                input wire [1:0] En,
                input wire [8:0] Din,
                output reg [8:0] Dout);
                
    always @(posedge clk) begin
        if (reset == 1'b1) begin
            Dout <= 9'b000000000;
        end
        else if (En == 2'b00) begin
            Dout <= Din;
        end
        else begin
            Dout <= "ZZZZZZZZZ";
        end
    end

endmodule