按键切换检测PWM波的占空比，频率，幅度-Key change detection wave PWM duty cycle, frequency, amplitude

This example shows how to use, for debug purpose, the RCC_GetClocksFreq function to retrieve the current status and frequencies of different on chip clocks. You can see the RCC_ClockFreq structure content, which hold the frequencies of diffe

/* 流量程序第1版 Finish Date: 2011\2\21 改动日期：2011\7\15 版本号：U1.0 采用11.0592MHz外部晶振 显示方式：动态扫描 功能描述: 1.检测流量，单位1m3/min=60m3/h 2.检测范围，0~100m3/min 3.频率输出200-1000Hz 调试方法：0 调零，1 量程，2 线性，3 报警点，4 断电点，5 复电点，6 自检点，7 自检， 8 AD输入电压，9 灵敏