CalendarExtender : why did display Saturday and Sunday in the calendar

hi,

why in my Calendar, only display weekdays but no weekends ? How display all of it ? 

Below, are my codes:

<asp:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txtTarikh"
 Format="dd-MM-yyyy" CssClass="CalendarStyle" FirstDayOfWeek="Monday" ></asp:CalendarExtender>

Thanks