//////////////////////////////////////////////////////////////
//  4-bit loadable up-down counter          //////
//////////////////////////////////////////////////////////////

module counter(clk, rst, data, updown, load, data_out);

    input clk, rst, load;
    input updown;
    input [3:0] data;

    output reg [3:0] data_out;

    always @(posedge clk)
    begin
        if(rst)
            data_out <= 4'b0;
        else if(load)
            data_out <= data;
        else
            data_out <= ((updown)?(data_out + 1'b1):(data_out -1'b1));
    end

endmodule