Bind Dropdownlist inside GridView at EditMode in ASP.Net

hi all, 

I have a dropdown list control in <Edit Template>, for new records, I populate this DDL from a sqldatasource control. 

In Edit mode, (click Edit link in gridView), i bind data from a Stored Procedure in code behind.

How can i set value from database as Selected in DDL?

this is my afected code:

<EditItemTemplate>
                    <asp:Label ID="lblFacturarA" runat="server" Text='<%# Eval("facturar_a")%>'>
                    </asp:Label>
                    <asp:DropDownList 
                        ID="ddlFacturarA"  
                        CssClass="txt"   
                        runat="server" 
                         
                        DataSourceID="sqlDataSource1"
                        DataTextField="Zona" 
                        DataValueField="Zona" 
                        AppendDataBoundItems="True" 
                        AutoPostBack="True" 
                        ValidationGroup="rfNewLine">
                    </asp:DropDownList>

sqldatasource 

        
<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
    ConnectionString="<%$ ConnectionStrings:DDLGrupoMpw %>" 
    SelectCommand="usp_GrupoMpw_SELECT" SelectCommandType="StoredProcedure">
</asp:SqlDataSource>

this is only for new record

 How can i set value from database as default or Selectd in DDL?

thanks for help!!!