Here txtamt is the item template of a gridview and uptotamt is outside of the gridview.
<asp:UpdatePanel ID="UpTotAmt" runat="server" RenderMode="Inline" UpdateMode="Conditional">
<ContentTemplate>
<asp:TextBox ID="txttot" runat="server" CssClass="texttot" Width="180px"
Enabled="False" ></asp:TextBox>
</ContentTemplate>
<Triggers >
<asp:AsyncPostBackTrigger ControlID="txtamt" EventName="TextChanged" />
</Triggers>
</asp:UpdatePanel>