How to get multiple values as input to Select Command from textbox

I have a textbox in asp page wherein it should take multiple values separated by comma's to select command as input. The same I have done using C# page, but now trying to have the entire query in aspx page itself.

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
//GridView code
<asp:SqlDataSource ID="Sql1" runat="server" ConnectionString="test"
        SelectCommand="SELECT Name 
                        WHERE ID IN (@TEST_ID) from EMPLOYEE 
                        ORDER BY 'Name'">
        <SelectParameters>
            <asp:ControlParameter ControlID="TextBox1" Name="TEST_ID" PropertyName="Text" />
        </SelectParameters>
    </asp:SqlDataSource>