stm32f103c8t6用中断采出来的数来回跳？怎么样才能稳定下来？

STM32F103C8T6用中断采集AD677的16位数字信号，采的是2V基准电压，采出的值在0.5和3之间来回跳。
AD677的参考电压是5V，AD677采样时序如下
串口助手得到的数如下，我用fb判断busy是否为高，用fa判断busy是否为低，所以fb和fa之间的数就是采出来的数

我用外部中断检测SCLK的上升沿，检测到上升沿就进入中断，把sdata的值赋给data，采完16位通过usart发到上位机，以下是代码

#define SAMPLE_HIGH()     GPIO_SetBits(GPIOA, GPIO_Pin_4)
#define SAMPLE_LOW()      GPIO_ResetBits(GPIOA, GPIO_Pin_4)
#define CLK_HIGH()        GPIO_SetBits(GPIOA, GPIO_Pin_6)
#define CLK_LOW()         GPIO_ResetBits(GPIOA, GPIO_Pin_6)
#define CAL_HIGH()        GPIO_SetBits(GPIOA, GPIO_Pin_7)
#define CAL_LOW()         GPIO_ResetBits(GPIOA, GPIO_Pin_7)

#define READ_SDATA()      GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_8)
#define READ_BUSY()       GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11)
#define READ_SCLK()       GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_10)
#define READ_CLK()        GPIO_ReadOutputDataBit(GPIOA, GPIO_Pin_6)

#define ResetCOUNTER()    TIM_SetCounter(TIM3, 0)

volatile uint16_t data = 0;             // 最终的16位数据
volatile uint8_t bitCounter = 0;        // 位计数器
volatile uint8_t dataReady = 0;         // 数据就绪标志

void GPIO_ENABLE(uint32_t RCC_APB2Periph, GPIO_TypeDef* GPIOx, GPIOMode_TypeDef GPIO_Mode, uint16_t GPIO_Pin, GPIOSpeed_TypeDef GPIO_Speed)
{
	RCC_APB2PeriphClockCmd(RCC_APB2Periph, ENABLE);
	
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode;
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed;
	GPIO_Init(GPIOx, &GPIO_InitStructure);
}

void AD_Init(void)
{
	GPIO_ENABLE(RCC_APB2Periph_GPIOA, GPIOA, GPIO_Mode_AF_PP, GPIO_Pin_6, GPIO_Speed_50MHz);
	GPIO_ENABLE(RCC_APB2Periph_GPIOA, GPIOA, GPIO_Mode_Out_PP, GPIO_Pin_4 | GPIO_Pin_7, GPIO_Speed_50MHz);
	GPIO_ENABLE(RCC_APB2Periph_GPIOA, GPIOA, GPIO_Mode_IN_FLOATING, GPIO_Pin_8, GPIO_Speed_50MHz);
	GPIO_ENABLE(RCC_APB2Periph_GPIOB, GPIOB, GPIO_Mode_IN_FLOATING, GPIO_Pin_10 | GPIO_Pin_11, GPIO_Speed_50MHz);
	
	//A6、tim3ch1初始化，输出pwm波
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
	
	TIM_InternalClockConfig(TIM3);
	
	TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
	TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
	TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
	TIM_TimeBaseInitStruct.TIM_Period = 1000 - 1;   //ARR
	TIM_TimeBaseInitStruct.TIM_Prescaler = 4 - 1; //PSC，18kHz
	TIM_TimeBaseInitStruct.TIM_RepetitionCounter = 0;
	TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitStruct);
	
	TIM_OCInitTypeDef TIM_OCInitStruct;
	TIM_OCStructInit(&TIM_OCInitStruct);
	TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
	TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_Low;
	TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
	TIM_OCInitStruct.TIM_Pulse = 500;  //CCR
	
	TIM_OC1Init(TIM3, &TIM_OCInitStruct);
	
//	TIM_Cmd(TIM3, ENABLE);
}

void PB10EXTI_Init(void)
{
	//B10、EXTI
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);
 
	//设置IO口与中断线的映射关系
	GPIO_EXTILineConfig(GPIO_PortSourceGPIOB,GPIO_PinSource10);
	
	//初始化线上中断
	EXTI_InitTypeDef EXTI_InitStruct;
	EXTI_InitStruct.EXTI_Line = EXTI_Line10;
	EXTI_InitStruct.EXTI_LineCmd = ENABLE;
	EXTI_InitStruct.EXTI_Mode = EXTI_Mode_Interrupt;
	EXTI_InitStruct.EXTI_Trigger = EXTI_Trigger_Rising;//上升沿触发
	EXTI_Init(&EXTI_InitStruct);
	
	//配置中断分组
	NVIC_InitTypeDef NVIC_InitStruct;
	NVIC_InitStruct.NVIC_IRQChannel = EXTI15_10_IRQn;
	NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
	NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 1;
	NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
	NVIC_Init(&NVIC_InitStruct);
}

void EXTI15_10_IRQHandler(void)
{
	int8_t temp;
//    static uint32_t lastCaptureTime = 0;
//    uint32_t currentCaptureTime;
    
    if(EXTI_GetITStatus(EXTI_Line10) != RESET) 
    {
        EXTI_ClearITPendingBit(EXTI_Line10);//重置标志位
        
//        currentCaptureTime = TIM_GetCapture1(TIM1);
//        for(volatile int i = 0; i < 25; i++);
        // 接收一位数据
        if(bitCounter < 16) 
		{   
            // 将读取的位存入capturedValue
            data = (data << 1) | READ_SDATA();
            bitCounter++;
            
            // 当收到16位数据时设置数据就绪标志
            if(bitCounter == 16) 
			{
                dataReady = 1;
                bitCounter = 0;  // 重置位计数器，准备下一次接收
					if(dataReady == 1)
					{
						temp = (data >> 8) & 0xFF;  //高8位
						Serial_SendByte(temp);
		
						temp = (data & 0xFF);  //低8位
						Serial_SendByte(temp);
	
//						Serial_SendByte(0xF7);//发送完成
		
						dataReady = 0;//重置标志位
					}
			}
        }
//        lastCaptureTime = currentCaptureTime;

    }
}