本例程通过GPIO外部中断控制LED的电平翻转。每一次按键按下都会产生一个中断，在中断服务子程序中的代码去控制LED电平的翻转。与循环扫描按键不同，外部中断方式占用更小的CPU开销。

1 外部中断的初始化

void EXTIX_Init(void)
{
    EXTI_InitTypeDef EXTI_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE);                      

    KEY_Init();                                                               

    SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource5);

    EXTI_InitStructure.EXTI_Line = EXTI_Line0;
    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;                      
    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
    EXTI_Init(&EXTI_InitStructure);                                            

    NVIC_InitStructure.NVIC_IRQChannel = EXTI0_1_IRQn;                          
    NVIC_InitStructure.NVIC_IRQChannelPriority = 0x01;                          
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;                             
    NVIC_Init(&NVIC_InitStructure);

}

2 中断服务子程序

void EXTI0_1_IRQHandler(void)
{
    for(EXTI_DELAY = 0; EXTI_DELAY < 1000; EXTI_DELAY++);
    if(KEY1 == 0) {
        LED1_TOGGLE();
    }
    EXTI_ClearFlag(EXTI_Line0);                                                 
}

3 main函数

int main(void)
{
    delay_init();
    LED_Init();
    KEY_Init();
    EXTIX_Init();
    while(1) {
    }
}