update command not working in gridview

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Gridview

Hi,
My update command is not working. I have pass 3 parameters. 2 parameter is dropdownvalue and one is bound fields. How to pass dropdown values in update parameter?
My code is below

<asp:GridView ID="grdDeptEmp" runat="server" AutoGenerateColumns="False"
                       DataKeyNames="emp_number" Cssclass="tabulardata" DataSourceID="dsOtherDept1"
                   class="tabulardata" width="100%" HorizontalAlign="Center"  OnRowCancelingEdit="grdDeptEmp_RowCancelingEdit"
                   OnRowDataBound="grdDeptEmp_RowDataBound" OnRowEditing="grdDeptEmp_RowEditing" OnRowUpdating="grdDeptEmp_RowUpdating"
                   OnRowCommand="grdDeptEmp_RowCommand" ShowFooter="True"
                       OnRowDeleting="grdDeptEmp_RowDeleting" AllowPaging="True">
                             <columns>
                               <asp:TemplateField HeaderText="Sl.No" ItemStyle-HorizontalAlign="Center"
                                        ItemStyle-Width="2%">
                                        <itemtemplate>
                                            <asp:Label ID="Sno" runat="server">
                                        </itemtemplate>
                                        <itemstyle horizontalalign="Center" />

                               <asp:TemplateField HeaderText="EmpNumber"  HeaderStyle-HorizontalAlign="Left">
                                   <edititemtemplate>
                                       <asp:Label ID="lblEmpNo" runat="server" Text='<%# Bind("emp_number") %>'>
                                   </edititemtemplate>
                                   <itemtemplate>
                                       <asp:Label ID="lblEmpNo" runat="server" Text='<%# Bind("emp_number") %>'>
                                   </itemtemplate>
                                   <HeaderStyle HorizontalAlign="Left" />

                               <%-- <asp:BoundField HeaderText="Emp_Number" Visible="true" DataField="emp_number"
                                        ItemStyle-HorizontalAlign="center" ReadOnly="true" SortExpression="emp_number">
                                        <itemstyle horizontalalign="Center" width="5%" />
                                --%>
                               <asp:BoundField HeaderText="Name" DataField="name"
                                        ItemStyle-HorizontalAlign="center" ReadOnly="true" SortExpression="name">
                                        <itemstyle horizontalalign="Center" width="17%" />

                                <asp:BoundField HeaderText="Designation" DataField="emp_designation"
                                        ItemStyle-HorizontalAlign="center" ReadOnly="true" SortExpression="emp_designation">
                                        <itemstyle horizontalalign="Center" width="17%" />

                                <asp:TemplateField HeaderText="From Period" HeaderStyle-HorizontalAlign="Left">
                                   <edititemtemplate>
                                       <asp:DropDownList ID="cmbFrm" runat="server" Style="width: 150px;"
                                           DataSourceID="dsOtherDept1" DataTextField="FromPeriod" DataValueField="FromPeriod"
                                           AppendDataBoundItems="true">
                                           <asp:ListItem Text="Please Select" Value="">

                                   </edititemtemplate>
                                   <itemtemplate>
                                       <asp:Label ID="lblFrm" runat="server" Text='<%# Eval("FromPeriod") %>'>
                                   </itemtemplate>
                                    <HeaderStyle HorizontalAlign="Left" />

                                <asp:TemplateField HeaderText="To Period" HeaderStyle-HorizontalAlign="Left">
                                   <edititemtemplate>
                                       <asp:DropDownList ID="cmbTo" runat="server" Style="width: 150px;"
                                           DataSourceID="dsOtherDept1" DataTextField="ToPeriod" DataValueField="ToPeriod"
                                           AppendDataBoundItems="true">
                                           <asp:ListItem Text="Please Select" Value="">

                                   </edititemtemplate>
                                   <itemtemplate>
                                       <asp:Label ID="lblTo" runat="server" Text='<%# Eval("ToPeriod") %>'>
                                   </itemtemplate>
                                    <HeaderStyle HorizontalAlign="Left" />

                               <asp:TemplateField HeaderText="Edit" ShowHeader="False" HeaderStyle-HorizontalAlign="Left">
                                   <edititemtemplate>
                                       <asp:LinkButton ID="lbkUpdate" runat="server" CausesValidation="True" CommandName="Update" Text="Update">
                                       <asp:LinkButton ID="lnkCancel" runat="server" CausesValidation="False" CommandName="Cancel" Text="Cancel">
                                   </edititemtemplate>
                                   <itemtemplate>
                                       <asp:LinkButton ID="lnkEdit" runat="server" CausesValidation="False" CommandName="Edit" Text="Edit">
                                   </itemtemplate>
                                   <HeaderStyle HorizontalAlign="Left" />

                               <asp:CommandField HeaderText="Delete" ShowDeleteButton="True" ShowHeader="True" />
                           </columns>

                   <asp:SqlDataSource ID="dsOtherDept1" runat="server"
                           ConnectionString="<%$ConnectionStrings:MPP%>"
                           SelectCommand="Select distinct V.emp_number as emp_number,emp_name+' '+emp_initial as name,emp_designation,Manpower_Division_ID,FromPeriod, ToPeriod from idpeapp.dbo.view_employee V inner join OtherDeptEmp O on V.emp_number = O.emp_number order by name"
                           UpdateCommand="update OtherDeptEmp set FromPeriod=@FromPeriod,ToPeriod=@ToPeriod where emp_number=@emp_number">
                           <updateparameters>
                                 <asp:Parameter Name="FromPeriod" Size="20" Type="String" />
                                 <asp:Parameter Name="ToPeriod" Size="20" Type="String" />
                                 <asp:Parameter Name="emp_number" Type="Int32" />
                            </updateparameters>