STM32F407的TIM1输出的PWM信号是正负极性的怎么回事

dy007

   用STM32F407的TIM1输出一个1M的PWM信号，不用选项的是 TIM_OCMode_PWM2（反极性） 还是 TIM_OCMode_PWM1（正极性），输出的PWM信号都是一样的，都是正负极性的，用示波器的耦合交流来看，大家帮忙看看是怎么回事是哪里设置有问题恩？

TIM_TimeBaseStructure.TIM_Period = 168-1; //查数据手册可知，TIM1与TIM8为16位自动装载
TIM_TimeBaseStructure.TIM_Prescaler =1-1;      //分频为168M
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;//向上计数
TIM_TimeBaseStructure.TIM_RepetitionCounter = 0x0;
TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);
 
TIM_OCStructInit(&TIM_OCInitStructure);  //填入缺省值，其中后几项只对TIM1和TIM8有效
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //PWM1为正常占空比模式，PWM2为反极性模式
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //输出允许
TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable; //互补输出允许
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;  //High为占空比高极性，此时占空比为20%；Low则为反极性，占空比为80%
TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;//互补输出，与以上相反
TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;

TIM_OCInitStructure.TIM_Pulse = 84;
TIM_OC2Init(TIM1, &TIM_OCInitStructure);

TIM_OC1PreloadConfig(TIM1, TIM_OCPreload_Enable);//CCR自动装载默认也是打开的
TIM_ARRPreloadConfig(TIM1, ENABLE); //ARR自动装载默认是打开的，可以不设置

TIM_ClearFlag(TIM1, TIM_FLAG_Update);
TIM_ITConfig(TIM1, TIM_IT_Update, ENABLE);
 TIM_BDTRConfig(TIM1, &TIM_BDTRInitStructure);

TIM_Cmd(TIM1, ENABLE); //使能TIM1定时器
TIM_CtrlPWMOutputs(TIM1, ENABLE);//使能TIM1的PWM输出，TIM1与TIM8有效

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