原理：

• 当计数值向上溢出或者向下溢出时，对应增加和减少重装载的值 0xFFFF。
• 对此读取 （TIM1->CNT + abs_count）是为了防止中途被中断打断而破坏组包数据。不建议屏蔽中断去读取，查询过快时也会造成中断开启关闭过快，会造成系统实时性下降。

static int abs_count = 0;//绝对位置

void Speed_ENC(void)
{
	GPIO_InitTypeDef GPIO_InitStructure;
	NVIC_InitTypeDef NVIC_InitStructure;

	TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

	RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);   
	RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOE, ENABLE);  

 
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_11;  
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
	GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
	GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

	GPIO_Init(GPIOE, &GPIO_InitStructure);

	GPIO_PinAFConfig(GPIOE, GPIO_PinSource9, GPIO_AF_TIM1);  
	GPIO_PinAFConfig(GPIOE, GPIO_PinSource11, GPIO_AF_TIM1);  

	TIM_TimeBaseStructure.TIM_Prescaler = 0;  
	TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
	TIM_TimeBaseStructure.TIM_Period = 0xFFFF; 

	TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);

	TIM_EncoderInterfaceConfig(TIM1, TIM_EncoderMode_TI12, TIM_ICPolarity_Rising, TIM_ICPolarity_Rising);

	TIM_Cmd(TIM1, ENABLE);  

	NVIC_InitStructure.NVIC_IRQChannel = TIM1_UP_TIM10_IRQn;
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2; 
	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;		 
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;			 
	NVIC_Init(&NVIC_InitStructure);							 

	TIM_ClearITPendingBit(TIM1, TIM_IT_Update);

	TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE);
}

void TIM1_UP_TIM10_IRQHandler(void)
{
	if (TIM_GetITStatus(TIM1, TIM_IT_Update) != RESET) //溢出
	{
		if (TIM1->CR1 & (1 << 4))
			abs_count -= 0xFFFF;
		else
			abs_count += 0xFFFF;
		TIM_ClearITPendingBit(TIM1, TIM_IT_Update);
	}
}

//***************设置当前绝对位置**************
void TIM1_Encoder_Write(int data)
{
	TIM_ITConfig(TIM1, TIM_IT_Update, DISABLE);
	TIM1->CNT = 0;
	abs_count = data;
	TIM_ClearITPendingBit(TIM1, TIM_IT_Update);
	TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE);
}

//*************读计当前绝对位置**************
int TIM1_Encoder_Read(void)
{
	int cnt1 = TIM1->CNT + abs_count;
	int cnt2 = TIM1->CNT + abs_count;
	if (cnt1 == cnt2)
		return cnt1; //未出现中断
	else
		return TIM1->CNT + abs_count; //可能刚发生中断
}