pwm对于电机的转速调整，我们是采用脉宽调制（PWM）办法，控制电机的时候，电源并非连续地向电机供电，而是在一个特定的频率下以方波脉冲的形式提供电能。不同占空比的方波信号能对电机起到调速作用，这是因为电机实际上是一个大电感，它有阻碍输入电流和电压突变的能力，因此脉冲输入信号被平均分配到作用时间上，这样，改变在始能端PE2  和PD5  上输入方波的占空比就能改变加在电机两端的电压大小，从而改变了转速-PWM for motor speed adjustment, we are using pulse width modulation (PWM) to control the motor, supply power to motor power supply is not continuous but Israel under a specific frequency pulse in the form of power. Different duty ratio of the square wave signal to the motor speed control effect, this is because the motor is in fact a large inductance, it has the ability to hinder the input current and voltage mutation, the average pulse input signal is assigned to a role in time, so that changes at the beginning to end PE2 and PD5 input square wave duty ratio can change in voltage at the ends of the motor size, thus changing the rotational speed