使用STM8的TIM2输入补获功能测PWM的占空比和周期，把被测信号接到TIM1的CH1，当有PWM时进入中断更改触发边沿，即可以使用一个通道测量高电平和低电平的时间，得到占空比和周期-Use the STM8 TIM2 input capture function PWM duty cycle and period measurement, the measured signal received TIM1 of CH1, when a PWM into the interrupt trigg