How to Show the progressbar to Adding PostBackTriggers and AsyncPostBackTriggers to UpdatePanel in asp.net?

I have a page with a ToolkitScriptManager and three update panels each update panel have triggers based on controls , now my problem is fire any server side events show the progressbar like percentages Example, How to show like that in PostBackTriggers and AsyncPostBackTriggers controls , my code is
<asp:UpdatePanel ID="up1" runat="server" ChildrenAsTriggers="true" UpdateMode="Conditional"> <Triggers> <asp:AsyncPostBackTrigger ControlID="TxtZip" EventName="textchanged" /> </Triggers> <ContentTemplate> <asp:TextBox ID="TxtZip" runat="server" AutoPostBack="true" ClientIDMode="Static" MaxLength="6" onkeypress="return isNumberKey(event)" CssClass="txtstyle" OnTextChanged="TxtZip_TextChanged"></asp:TextBox> </ContentTemplate> </asp:UpdatePanel> <asp:Up ...