Populate (Bind) ListBox using three tier architecture in ASP.Net

i want to display Emp Id from database to ListBox in c# web application.

but having no much idea with three tier i want to display record using three tier architecture.

i have used below code to do this. but there is no output.

how to fill ListBox using three tier architecture in c# web application?

DAL

public static DataTable fillListbox()
{
    string conn = ConfigurationManager.ConnectionStrings["constring"].ConnectionString;
    SqlConnection con = new SqlConnection(conn);
    con.Open();
    string sqlSelect = "SELECT EMP_ID From EMPLOYEE_MASTER";
    SqlCommand cmd = new SqlCommand(sqlSelect, con);
    SqlDataReader dr = cmd.ExecuteReader();
    DataTable dtt = null;
    if (dr.HasRows)
    {
        dtt = new DataTable("EMPLOYEE_MASTER");
        dr.Read();
        return dtt;         
    }
    if (cmd != null)
    {
        con.Close();
        cmd.Dispose();
        cmd = null;
    }
    return dtt;
}

 BAL 

public static DataTable Get_EMPID()
{
    return DAL.DAL.fillListbox();
}

PL 

private void BindEMPID()
{
    BAL.BAL empLstbox = new BAL.BAL();
    DataTable dt = BAL.BAL.Get_EMPID();
    empListbox.DataTextField = "EMP_ID";
    empListbox.DataValueField = "EMP_ID";
    empListbox.DataBind();
}