说明：  一个用DSP开发PWM波的程序。可以产生共六路，三路正的，三路反的PWM波，这 我毕设做的，得了我们系最高分。
(DSP development of a PWM wave procedures. Can have a total of six road, the road is three, three anti-road PWM wave, I set up so complete, we achieved is the highest number of points.)