使用PWM方式来产生一个1KHz左右的正弦波，幅度为0-Vcc/2

pwm波恒流源程序，输出1khz的矩形波，可调范围为10 到80 ，步进为5 -pwm wave constant current source, the output of a rectangular wave of 1khz, the adjustable range of 10 to 80 , the stepping to 5

2812 PWM程序：初始化EVA，使得PWM1和PWM2输出互补的周期为1KHz的PWM波，占空比初始化为10 ，死区时间为4.27us-2812 PWM procedures: Initialize EVA makes PWM1 and PWM2 output complementary cycle 1KHz PWM wave, 10 duty cycle initialization, deadtime 4.27us

Method to generate sinewave PWM module with TMR2 at 100 ticks (20uS) giving 100 possible PWM resolution steps. However sine table goes from 14 to 86 PWM or a total height range of 73 steps. Sine table has 50 entries over one full 1kHz cy