555计数学习和掌握单片机定时/计数器的计数模式，通过555模块产生不同频率的方波信号，输入到单片机计数脉冲输入T0/T1引脚上，通过编程可以统计输入的脉冲数或输入脉冲频率-555 counts to study and master microcontroller timer/counter counting mode, the module produced by 555 different frequency square wave signal input to the MCU pin count pulse input T0/T1, statistical input can be programmed to pulse number or frequency of the input pulse