void Tim3_Init(u16 period_num)
{
        TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
        RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
        TIM_DeInit(TIM3);
        TIM_TimeBaseStructure.TIM_Period=period_num;
        //prescaler is 1200,that is 72000000/72/500=2000Hz;
        TIM_TimeBaseStructure.TIM_Prescaler=72-1;
        //set clock division
        TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1; //or TIM_CKD_DIV2 or TIM_CKD_DIV4
        //count up
        TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;       
        TIM_TimeBaseInit(TIM3,&TIM_TimeBaseStructure);
        TIM_ClearITPendingBit(TIM3,TIM_IT_Update);
        //TIM2 overflow interrupt enable
        TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE);
        //clear the TIM2 overflow interrupt flag
        TIM_ClearFlag(TIM3,TIM_FLAG_Update);
        //enable TIM2
        TIM_Cmd(TIM3,ENABLE);         
}为什么我一启动定时器，状态寄存器里的值是0x1f，无法清除！定时器有计数但却一直进不了中断！求指教啊！！

帮顶，坛友请帮忙看看

解决了吗？