说明：  步进电机的速度控制通过单片机发出的脉冲频率来实现。软件分配方式，可以采用调整两个控制字之间的时间间隔来实现。硬件脉冲分配方式，可以控制步进脉冲的频率来调速。
(stepper motor speed control of the MCU by pulse frequency is to be achieved. Software distribution, and the adjustment can be used to control two characters between the time interval is to be achieved. Hardware pulse distribution, and can be controlled stepper pulse frequency to the governor.)