我在定時器3的例程上面改，改了很久都沒改好，百度看別人說定時器1和定時器8需要額外的指令用于PWM輸出，今天下午硬件的人來要東西了，來不及研究了，于是網上找了個定時器8的4個通道全部可以輸出的例程記錄一下，已經經過本人試驗是OK的。

1.調用：

TIM8_PWM_Init(1439 ,0);    //不分頻。PWM頻率=72000000/1440=50Khz

2.函數源碼：

//TIM8 PWM部分初始化 
//PWM輸出初始化
//arr：自動重裝值
//psc：時鐘預分頻數
void TIM8_PWM_Init(u16 arr,u16 psc)
{  
  GPIO_InitTypeDef GPIO_InitStructure;
  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
  TIM_OCInitTypeDef  TIM_OCInitStructure;


  RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM8, ENABLE); //使能定時器3時鐘
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE);  //使能GPIO外設和AFIO復用功能模塊時鐘
  
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6|GPIO_Pin_7|GPIO_Pin_8|GPIO_Pin_9; //TIM_CH2
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  //復用推挽輸出
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_Init(GPIOC, &GPIO_InitStructure);//初始化GPIO
  
  //初始化TIM8
  TIM_TimeBaseStructure.TIM_Period = arr; //設置在下一個更新事件裝入活動的自動重裝載寄存器周期的值
  TIM_TimeBaseStructure.TIM_Prescaler =psc; //設置用來作為TIMx時鐘頻率除數的預分頻值
  TIM_TimeBaseStructure.TIM_ClockDivision = 0; //設置時鐘分割:TDTS = Tck_tim
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM向上計數模式
  TIM_TimeBaseInit(TIM8, &TIM_TimeBaseStructure); //根據TIM_TimeBaseInitStruct中指定的參數初始化TIMx的時間基數單位


  //初始化TIM8 Channel2 PWM模式  
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //選擇定時器模式:TIM脈沖寬度調制模式2
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比較輸出使能
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset ;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low ; //輸出極性:TIM輸出比較極性高
  TIM_OC1Init(TIM8, &TIM_OCInitStructure);  //根據T指定的參數初始化外設TIM8 OC2


  TIM_OC1PreloadConfig(TIM8, TIM_OCPreload_Enable);  //使能TIM8在CCR2上的預裝載寄存器


  TIM_SetCompare1(TIM8,474);


  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //選擇定時器模式:TIM脈沖寬度調制模式2
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比較輸出使能
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset ;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low ; //輸出極性:TIM輸出比較極性高
  TIM_OC2Init(TIM8, &TIM_OCInitStructure);  //根據T指定的參數初始化外設TIM8 OC2


  TIM_OC2PreloadConfig(TIM8, TIM_OCPreload_Enable);  //使能TIM8在CCR2上的預裝載寄存器


  TIM_SetCompare2(TIM8,700);


  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //選擇定時器模式:TIM脈沖寬度調制模式2
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比較輸出使能
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset ;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low ; //輸出極性:TIM輸出比較極性高
  TIM_OC3Init(TIM8, &TIM_OCInitStructure);  //根據T指定的參數初始化外設TIM8 OC2


  TIM_OC3PreloadConfig(TIM8, TIM_OCPreload_Enable);  //使能TIM8在CCR2上的預裝載寄存器


  TIM_SetCompare3(TIM8,900);


  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; //選擇定時器模式:TIM脈沖寬度調制模式2
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //比較輸出使能
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Reset ;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low ; //輸出極性:TIM輸出比較極性高
  TIM_OC4Init(TIM8, &TIM_OCInitStructure);  //根據T指定的參數初始化外設TIM8 OC2


  TIM_OC4PreloadConfig(TIM8, TIM_OCPreload_Enable);  //使能TIM8在CCR2上的預裝載寄存器


  TIM_SetCompare4(TIM8,1200);


  TIM_Cmd(TIM8, ENABLE);  //不使能TIM8


  TIM_CtrlPWMOutputs(TIM8,ENABLE);   
}