my97时间控件结束时间不能小于开始时间

<tr>
<th>开始日期</th>
<td>
<input type="text" id="startdate" name="startdate"  width="100px"  onclick="WdatePicker({readOnly:true,dateFmt:'yyyy-MM-dd HH:mm:ss',maxDate:'#F{$dp.$D(\'enddate\')}'})" />
</td>
<th>结束日期</th>
<td >
<input type="text" id="enddate" name="enddate"  width="100px"  onclick="WdatePicker({readOnly:true,dateFmt:'yyyy-MM-dd HH:mm:ss',minDate:'#F{$dp.$D(\'startdate\')}'})" />
</td>
</tr>