说明：  * 超声波测距程序 * 使用一个位定时器(定时器0模式1)和一个外部中断实现超声波测距 * * 需要调用的函数： * void HC_RS04_Driver()； 超声波测距驱动函数，需在【主函数】中调用 * void EchoExint0()； 回响时间计算,需在【外部中断】中调用 * void HC_RS04_Start()； 超声波开始测距触发函数，需在【定时器中断】中调用 * * 优点：占用单片机资源少，因使用定时器中断计时回响时间， * 不会影响的其他状态监测。使用起来方便 * 缺点：测量精度不高，测量300cm时有5cm左右的误差 * * 晶振频率：11.0592 MHz * 测量距离保存在 int 型全局变量 detection_range 中单位"cm"
(* ultrasonic distance measuring program * using a bit timer (timer 0 mode 1) and an external interrupt to achieve ultrasonic ranging. * * the function that needs to be called: * void HC_RS04_Driver (); the ultrasonic ranging drive function needs to be called in the main function. * void EchoExint0 (); reverberation time calculation, called in external interrupt. * void HC_RS04_Start (); the starting function of the ultrasonic ranging start is called in the timer interrupt. * advantages: occupy less MCU resources, because timer interrupt time reverberation time. * other state monitoring that will not be affected. Easy to use Disadvantages: the measurement accuracy is not high, and the error is about 5cm when measuring 300cm. * crystal oscillator frequency: 11.0592 MHz * measuring distance is saved in the int global variable detection_range in the unit "cm".)