PWM頻率 = 計數(shù)器的更新頻率 72M/CRR+1/ARR+1 72M/(720-1)+1/(100-1)+1 = 1000HZ

占空比 = CRR/ARR+1；

分辨率：1/ARR +1

例：時鐘72M，ARR:100-1, PSC:720-1, CRR: 50

是一個輸出 1khz，50%占空比，分辨率為1%的PWM波的參數(shù)

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1.?RCC時鐘，定時器和GPIO外設(shè)打開

2.?配置時基單元，時鐘源選擇

3.?配置輸出比較單元

4.?配置GPIO，復(fù)用推挽輸出

5.?運(yùn)行控制

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void TIM_OC1Init(TIM_TypeDef* TIMx, TIM_OCInitTypeDef* TIM_OCInitStruct);

用結(jié)構(gòu)體控制輸出比較單元

1.RCC時鐘，定時器和GPIO外設(shè)打開

?RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

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2.配置時基單元，時鐘源選擇

TIM_InternalClockConfig(TIM2);//內(nèi)部時鐘

????TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;

????TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;

????TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;

????TIM_TimeBaseInitStruct.TIM_Period = 100 - 1;//ARR

????TIM_TimeBaseInitStruct.TIM_Prescaler = 720 - 1;//PSC 72M/720/100 = 1000

????TIM_TimeBaseInitStruct.TIM_RepetitionCounter = 0;

TIM_TimeBaseInit(TIM2,&TIM_TimeBaseInitStruct);

3.配置輸出比較單元

不同的輸出通道對應(yīng)不同的GPIO口

?TIM_OCInitTypeDef ?TIM_OCInitStruct;

????TIM_OCStructInit(&TIM_OCInitStruct);//結(jié)構(gòu)體賦初值，防止有參數(shù)沒定義到

????TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;

????TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;

????TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;

????TIM_OCInitStruct.TIM_Pulse = 0;//CCR的值

TIM_OC1Init(TIM2, &TIM_OCInitStruct);

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4.配置GPIO，復(fù)用推挽輸出

????RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);

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????#if 0 //如果需要使用引腳重定義 PWM波輸出PA0 -> PA15

????RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO, ENABLE);

????GPIO_PinRemapConfig(GPIO_PartialRemap1_TIM2,ENABLE);

????GPIO_PinRemapConfig(GPIO_Remap_SWJ_JTAGDisable, ENABLE);

????#endif

????GPIO_InitTypeDef GPIO_InitStruct;

????GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;//復(fù)用推挽，將控制權(quán)轉(zhuǎn)移給片上外設(shè)

????GPIO_InitStruct.GPIO_Pin = GPIO_Pin_0;//如果重映射，GPIO_Pin_15

????GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;

????GPIO_Init(GPIOA,&GPIO_InitStruct);

5.運(yùn)行控制

?TIM_Cmd(TIM2, ENABLE);

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更改CRR寄存器函數(shù)

?TIM_SetCompare1(TIM2, Compare);

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void PWM_SetCompare1(uint16_t Compare)

{

????TIM_SetCompare1(TIM2, Compare);

}

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呼吸燈效果

?for (i = 0; i <= 100; i++)

{

????PWM_SetCompare1(i);

????Delay_ms(10);

}

for (i = 0; i <= 100; i++)

{

????PWM_SetCompare1(100 - i);

????Delay_ms(10);

}

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