PWM波程序 可以用来控制电机调速，程序比较简单，这里只用了一个定时器就实现了。因为51单片机没有PWM波的寄存器，所以要自己用软件控制。-PWM waves program can be used to control motor speed, procedure is simple, here only a timer is realized. Because no PWM waves 51-series microcomputer to yourself, so with registers control software.