使用PWM6输出PWM信号,由KEY1控制PWM占空比,每按一次,按键将会改变一次PWM的占空比.（采用UCOS操作系统编程。）-Use PWM6 output PWM signal, KEY1 controlled by the PWM duty cycle, every time, a button will change the PWM duty cycle. (Using UCOS operating system programming.)