GridView textbox Navigation using Arrow(up/down) keys using asp.net 2008

<script language="javascript" type="text/javascript">
    function keyPressed(TB, e) {
        var rowscount = document.getElementById('<%=GridView1.ClientID%>').rows.length;
        if (e.keyCode == 40 || e.keyCode == 13) {
            if (TB.split("TextBox1_")[1] < (rowscount-2))
                document.getElementById(TB.split("TextBox1_")[0] + 'TextBox1_' + eval(TB.split("TextBox1_")[1] + '+1')).focus();

        }
        if (e.keyCode == 38) {
            if (TB.split("TextBox1_")[1] >= 1)
                document.getElementById(TB.split("TextBox1_")[0] + 'TextBox1_' + eval(TB.split("TextBox1_")[1] + '-1')).focus();
        }
    }
</script>

    <asp:GridView ID="GridView1" runat="server" AllowPaging="True"
        AllowSorting="True" AutoGenerateColumns="False" DataKeyNames="AccessTypeID"
        DataSourceID="SqlDataSource1">
        <Columns>
            <asp:TemplateField HeaderText="type" SortExpression="type">
                <ItemTemplate>
                    <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("type") %>'  onkeyup="keyPressed(this.id,event)"></asp:TextBox>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server"
        ConnectionString="<%$ ConnectionStrings:omfConnectionString %>"
        SelectCommand="SELECT * FROM [tblAccessType] WHERE ([type] LIKE '%' + @type + '%')">
        <SelectParameters>
            <asp:Parameter DefaultValue="work phone" Name="type" Type="String" />
        </SelectParameters>
    </asp:SqlDataSource>