说明：  步进电机控制设计，读取显示器上显示的正、反转命令，转速（16级）和转动步数后执行，转动步数减为零时停止转动。
(The stepper motor control design, the positive and reverse commands displayed on the display is read, executed after the speed (16) and the rotation step number, and stops rotating when the rotation number of steps is reduced to zero.)