7路PWM产生程序阅读

如下是7路PWM产生的程序解读，粘贴程序如下，并会在一些内容上做简单注释说明，以方便理解阅读，对于具体的产生原理需要阅读《STM32不完全手册》或是其它STM32的相关资料文档。使用库函数的方式完成功能实现，需要对库函数有一定的熟悉了解，相对于寄存器方式的方式更加快捷，但是对于初学者还是寄存器的方式更容易理解，加深学习效果。

 

程序的设计步骤为：

1、初始化系统时钟，使能相应的module的时钟；

2、GPIO的相应设置，使用GPIO的复用功能；

3、设置定时器的时基，采用的是内部时钟，主要设置频率、计数模式、分频倍频；

4、设置相应通道，包括比较寄存器的值、使能输出驱动、输出模式、输出极性、idle状态值

#include "stm32f10x.h"

TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

TIM_OCInitTypeDef  TIM_OCInitStructure;

uint16_t TimerPeriod = 0;

uint16_t Channel1Pulse = 0, Channel2Pulse = 0, Channel3Pulse = 0, Channel4Pulse = 0;

 

/* Private function prototypes -----------------------------------------------*/

void RCC_Configuration(void);      // 关于设备的时钟初始化在rcc.c的库文件中，startup文件启动时自动跳转至时钟设置处，在如下文档中只是做相应的module的时钟使能

void GPIO_Configuration(void);    // 设置 channel的GPIO，需要复用功能开启

 

int main(void)

{

  /*!< At this stage the microcontroller clock setting is already configured, 

       this is done through SystemInit() function which is called from startup

       file (startup_stm32f10x_xx.s) before to branch to application main.

       To reconfigure the default setting of SystemInit() function, refer to

       system_stm32f10x.c file

     */     

       

  /* System Clocks Configuration */

  RCC_Configuration();

 

  /* GPIO Configuration */

  GPIO_Configuration();

 

  /* TIM1 Configuration ---------------------------------------------------

   Generate 7 PWM signals with 4 different duty cycles:

   TIM1CLK = SystemCoreClock, Prescaler = 0, TIM1 counter clock = SystemCoreClock

   SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density

   and Connectivity line devices and to 24 MHz for Low-Density Value line and

   Medium-Density Value line devices

   

   The objective is to generate 7 PWM signal at 17.57 KHz:（72MHz/4097=17570Hz 所以反向计算定时器周期为如下公式）

     - TIM1_Period = (SystemCoreClock / 17570) - 1

   The channel 1 and channel 1N duty cycle is set to 50%

   The channel 2 and channel 2N duty cycle is set to 37.5%

   The channel 3 and channel 3N duty cycle is set to 25%

   The channel 4 duty cycle is set to 12.5%

   The Timer pulse is calculated as follows:

     - ChannelxPulse = DutyCycle * (TIM1_Period - 1) / 100

  ----------------------------------------------------------------------- */

  /* Compute the value to be set in ARR regiter to generate signal frequency at 17.57 Khz */

  TimerPeriod = (SystemCoreClock / 17570 ) - 1;

  /* Compute CCR1 value to generate a duty cycle at 50% for channel 1 and 1N */

  Channel1Pulse = (uint16_t) (((uint32_t) 5 * (TimerPeriod - 1)) / 10);

  /* Compute CCR2 value to generate a duty cycle at 37.5%  for channel 2 and 2N */

  Channel2Pulse = (uint16_t) (((uint32_t) 375 * (TimerPeriod - 1)) / 1000);

  /* Compute CCR3 value to generate a duty cycle at 25%  for channel 3 and 3N */

  Channel3Pulse = (uint16_t) (((uint32_t) 25 * (TimerPeriod - 1)) / 100);

  /* Compute CCR4 value to generate a duty cycle at 12.5%  for channel 4 */

  Channel4Pulse = (uint16_t) (((uint32_t) 125 * (TimerPeriod- 1)) / 1000);

 

  /* Time Base configuration 时基的设置*/    

  TIM_TimeBaseStructure.TIM_Prescaler = 0;

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseStructure.TIM_Period = TimerPeriod;

  TIM_TimeBaseStructure.TIM_ClockDivision = 0;

  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;

 

  TIM_TimeBaseInit(TIM1, &TIM_TimeBaseStructure);

 

  /* Channel 1, 2,3 and 4 Configuration in PWM mode */

  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;

  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;

  TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;

  TIM_OCInitStructure.TIM_Pulse = Channel1Pulse;

  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;

  TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;

  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;

  TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;

 

  TIM_OC1Init(TIM1, &TIM_OCInitStructure);

 

  TIM_OCInitStructure.TIM_Pulse = Channel2Pulse;

  TIM_OC2Init(TIM1, &TIM_OCInitStructure);

 

  TIM_OCInitStructure.TIM_Pulse = Channel3Pulse;

  TIM_OC3Init(TIM1, &TIM_OCInitStructure);

 

  TIM_OCInitStructure.TIM_Pulse = Channel4Pulse;

  TIM_OC4Init(TIM1, &TIM_OCInitStructure);

 

  /* TIM1 counter enable */

  TIM_Cmd(TIM1, ENABLE);

 

  /* TIM1 Main Output Enable */

  TIM_CtrlPWMOutputs(TIM1, ENABLE);

 

  while (1)

  {}

}

// 使能相应模块的时钟 

void RCC_Configuration(void)

{

  /* TIM1, GPIOA, GPIOB, GPIOE and AFIO clocks enable */

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1 | RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOE|

                         RCC_APB2Periph_GPIOB |RCC_APB2Periph_AFIO, ENABLE);

}

//子函数为相应的GPIO的设置

void GPIO_Configuration(void)

{

  GPIO_InitTypeDef GPIO_InitStructure;

 

  /* GPIOA Configuration: Channel 1, 2 and 3 as alternate function push-pull */

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9 | GPIO_Pin_10 | GPIO_Pin_11;

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOA, &GPIO_InitStructure);

 

  /* GPIOB Configuration: Channel 1N, 2N and 3N as alternate function push-pull */

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;

  GPIO_Init(GPIOB, &GPIO_InitStructure);

}

如下是示波器量测的波形，channel 2 GPIOA 的Pin 9

从图中可以看出信号是正确的，频率17.57KHz，占空比为37.5%