RCC->APB2ENR|=1<<11; //TIM2时钟使能
TIM1->CCMR1|=7<<12; //CH2 PWM2模式
TIM1->CCMR1|=1<<11; //CH2预装载使能
TIM1->ARR=1900; //设定计数器自动重装值
TIM1->  SC=0; //预分频器不分频
TIM1->CCR2=0x23; //设置占空比
TIM1->CR1=0x8000; //ARPE使能
TIM1->CCER|=1<<4; //OC2 输出使能
TIM1->CR1|=0x01; //使能定时器2
/*
RCC->APB1ENR|=1<<0; //TIM2时钟使能
TIM2->CCMR1|=7<<12; //CH2 PWM2模式
TIM2->CCMR1|=1<<11; //CH2预装载使能
TIM2->ARR=1900; //设定计数器自动重装值
TIM2->  SC=0; //预分频器不分频
TIM2->CCR2=0x23; //设置占空比
TIM2->CR1=0x8000; //ARPE使能
TIM2->CCER|=1<<4; //OC2 输出使能
TIM2->CR1|=0x01; //使能定时器2*/
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