说明：  给出了一路15级PWM波形输出，目的是使使用者练习PWM波的生成方法，使用者可在此程序的基础上稍加改动，自行编制另一路PWM波形或直接参考“实验十八”的双路PWM输出方法
(Given the way 15 PWM waveform output is intended to enable users to exercise PWM wave generation method, the user can be on the basis of this process is modified, produced its own way of another PWM waveform or direct reference to " experiment 18" in Dual PWM output method)