STM32f4 PWM output experimental code

The pwm.c source file code is as follows:  

//TIM14 PWM initialization  

//PWM output initialization

//arr: automatic reload value psc: clock pre-division number

void TIM14_PWM_Init(u32 arr,u32 psc)

{                  

  GPIO_InitTypeDef GPIO_InitStructure;

  TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

  TIM_OCInitTypeDef  TIM_OCInitStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM14,ENABLE); //TIM14 clock enable     

  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOF, ENABLE); //Enable PORTF clock

  GPIO_PinAFConfig(GPIOF,GPIO_PinSource9,GPIO_AF_TIM14); //GF9 is multiplexed as TIM14

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;                //GPIOF9  

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; //Multiplexing function

  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;  //速度 50MHz

  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; //Push-pull multiplexing output

  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;        //上拉

  GPIO_Init(GPIOF,&GPIO_InitStructure); //Initialize PF9

  TIM_TimeBaseStructure.TIM_Prescaler=psc; //Timer frequency division

  TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up; //Upward counting mode

  TIM_TimeBaseStructure.TIM_Period=arr; //Automatically reload value

  TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1;  

  TIM_TimeBaseInit(TIM14,&TIM_TimeBaseStructure); //Initialize timer 14

  //Initialize TIM14 Channel1 PWM mode    

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1; //PWM modulation mode 1

    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; //Comparison output enable

  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low; //Output polarity low

  TIM_OC1Init(TIM14, &TIM_OCInitStructure); //Initialize peripheral TIM1 4OC1

  TIM_OC1PreloadConfig(TIM14, TIM_OCPreload_Enable); //Enable preload register

     TIM_ARRPreloadConfig(TIM14,ENABLE);//ARPE enable  

  TIM_Cmd(TIM14, ENABLE); //Enable TIM14                     

}

This part of the code contains the first 5 steps of the PWM output settings introduced above. We will not talk about the settings of TIM14 here.  

Next, let's look at the main function in the main program as follows:

int main(void)

{  

  u16 led0pwmval=0;     

  u8 dir=1;

  NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2); //Set system interrupt priority group 2

  delay_init(168); //Initialize delay function

  uart_init(115200); //Initialize the serial port baud rate to 115200

    TIM14_PWM_Init(500-1,84-1); //The timer clock is 84M, the frequency division factor is 84, so the counting frequency

//84M/84=1Mhz, reload value 500, so PWM frequency is 1M/500=2Khz.      

     while(1)   

  {

      delay_ms(10);   

    if(dir)led0pwmval++; //dir==1 led0pwmval increments

    else led0pwmval--; //dir==0 led0pwmval decrement  

      if(led0pwmval>300)dir=0; //After led0pwmval reaches 300, the direction is decreasing

    if(led0pwmval==0)dir=1; //After led0pwmval decreases to 0, the direction changes to increasing

    TIM_SetCompare1(TIM14,led0pwmval); //Modify comparison value and duty cycle

  }

}

Here, we can see from the infinite loop function that we set the value of led0pwmval as the PWM comparison value, that is, we control the duty cycle of PWM through led0pwmval, and then control the value of led0pwmval from 0 to 300, and then from 300 to 0, and so on. Therefore, the brightness of DS0 will also change from dark to bright, and then from bright to dark as the duty cycle of the signal changes. As for the value here, why we take 300, because when the output duty cycle of PWM reaches this value, the brightness of our LED will not change much (although the maximum value can be set to 499), so it is unnecessary to design a value that is too large here. At this point, our software design is completed.