STM8S103F2P程序一直进入读ADC中断，为什么？

   我正在使用STM8S103F2P这个芯片， CPU没有使用外部晶振， 功能主要是读取电池电压， 我使用是 PD3 / AIN4 这个引脚，
程序一直进入读ADC中断。进入中断读到采集值为0.
程序如下：
main.c
--------------------------------------------------------
/* Includes ------------------------------------------------------------------*/
#include  quot;stm8s.h quot;
  uint16_t Conversion_Value = 0;
static void ADC_Config()
{
  GPIO_Init(GPIOC, (GPIO_Pin_TypeDef)GPIO_PIN_7, GPIO_MODE_OUT_PP_HIGH_FAST);
  GPIO_Init(GPIOC, (GPIO_Pin_TypeDef)GPIO_PIN_6, GPIO_MODE_OUT_PP_HIGH_FAST);
  
  /*  Init GPIO for ADC2 */
  GPIO_Init(GPIOD, GPIO_PIN_3, GPIO_MODE_IN_FL_NO_IT);
  
  /* De-Init ADC peripheral*/
  ADC1_DeInit();

  /* Init ADC2 peripheral */
  ADC1_Init(ADC1_CONVERSIONMODE_CONTINUOUS, ADC1_CHANNEL_9, ADC1_PRESSEL_FCPU_D2, ADC1_EXTTRIG_TIM, DISABLE, ADC1_ALIGN_RIGHT, ADC1_SCHMITTTRIG_CHANNEL9, DISABLE);

  /* Enable EOC interrupt */
  ADC1_ITConfig(ADC1_IT_EOCIE, ENABLE);

  /* Enable general interrupts */  
  enableInterrupts();
  
  /*Start Conversion */
  ADC1_StartConversion();
}
void main(void)
{
  ADC_Config();
  /* Infinite loop */
  while (1)
  {
  }
}

------------------------------------------------------------
stm8s_it.c
----------------------------------------------------------------
INTERRUPT_HANDLER(ADC1_IRQHandler, 22)
{
    /* In order to detect unexpected events during development,
       it is recommended to set a breakpoint on the following instruction.
    */
     /* Get converted value */
    Conversion_Value = ADC1_GetConversionValue();
    ADC1_ClearITPendingBit(ADC1_IT_EOC);  
}