版本 5aeece7879e148d9e91fe4d09a28d44ce713a4a4

embedded/PWM

Changes from 5aeece7879e148d9e91fe4d09a28d44ce713a4a4 to c30234bdf466e3e981a84a6706983132ecd4f2b3

---
title: Pulse-width modulation(PWM)
...

Introduction
============


又稱pulse-duration modulation(PDM)，是將類比信號轉為脈波的一種技術。

為何需要PWM？雖然類比電壓可直接用來控制，但類比電路控制信號容易隨時間漂移，功耗大。

.. image:: /pwm.png

如圖所示，PWM 電路主要功能是將輸入電壓的振幅轉換成脈衝寬度。一般轉換後脈波的週期固定，脈波的占空比(duty cycle)會依類比信號的大小而改變，可用來控制燈泡亮度、馬達轉速等等，脈波寬度越大燈泡亮度越亮、馬達轉速越快。


Implementation
==============
PWM需要透過Timer來實現，STM32的Timer可分為以下幾種

- 基本定時器(TIM6 和 TIM7)
- 高級控制定時器(TIM1 和 TIM8)
- 通用定時器(TIMx):具有測量輸入信號的脈衝長度、產生輸出波形和PWM的功能。
  - clock來源 : 內部clock(CK_INT)、外部clock模式1(TIx)、外部clock模式2(ETR)、內部觸發輸入(ITRx)。
  - CK_INT -> AHB Prescaler(/1、2、...、512) -> APB1 Prescaler(/1、2、4、8、16) or APB2 Prescaler(/1、2、4、8、16)。
  - Time Base Configuration :

  .. image:: /up mode.bmp

-----------

  .. image:: /down mode.bmp

-----------

  .. image:: /center aligned.jpg


    - TIM_ClockDivision  - 採樣頻率基準，當連續採樣到N個有效電平時，才當作一次有效電平。
    - TIM_Prescaler  -  將TIMxCLK除以(TIM_Prescaler+1)
    - TIM_CounterMode  -  選擇計數模式
    - TIM_Period  -  TIMx_ARR，counter 週期

  - 輸出脈波週期 = (TIM_Period+1) * (TIM_Prescaler+1) * (TIM_ClockDivision+1) / TIMxCLK
  - PWM configuration
    - TIM_OCMode  - PWM模式
      - PWM 1 Mode : 在向上計數，TIMx_CNT<TIMx_CCRx時，輸出為1，否則輸出為0；在向下計數，TIMx_CNT>TIMx_CCRx時，輸出為0，否則輸出為1。
      - PWM 2 Mode : 在向上計數，TIMx_CNT<TIMx_CCRx時，輸出為0，否則輸出為1；在向下計數，TIMx_CNT>TIMx_CCRx時，輸出為1，否則輸出為0。

    - TIM_Pulse  -  TIMx_CCRx，脈衝寬度
    - TIM_OCPolarity  -  設置輸出極性，例如:TIM_OCPolarity_High PWM輸出關閉時默認為低電位。 
    


以LED為例：

.. image:: /timer.png

TIM_Prescaler = 499,TIM_ClockDivision=0,TIMxCLK=84MHz

輸出脈波週期 = (TIM_Period+1) * (TIM_Prescaler+1) * (TIM_ClockDivision+1) / TIMxCLK
           
           = (1999+1) * (499+1) * (0+1)/84000000 ≒ 0.012 s

0.012 s 遠小於人眼視覺暫留的時間(0.1~0.4s)，因此上圖的PWM 2 duty cycle(75%)>PWM 1 duty cycle(25%)，PWM 2 Mode看起來會比PWM 1 Mode亮。
0.012 s 遠小於人眼視覺暫留的時間(0.1~0.4s)，因此上圖的PWM 1 duty cycle(75%)>PWM 2 duty cycle(25%)，PWM 1 Mode看起來會比PWM 2 Mode亮。

-----------

Code_section
=============

//====set pin enable=================

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD  | RCC_AHB1Periph_GPIOB | RCC_AHB1Periph_GPIOA, ENABLE ); //開啟Pin腳 D B E提供使用

RCC_APB1PeriphClockCmd( RCC_APB1Periph_TIM4 | RCC_APB1Periph_TIM3, ENABLE ); //開啟Timer

- GPIO_PinAFConfig(GPIOD, GPIO_PinSource12, GPIO_AF_TIM4);
- GPIO_PinAFConfig(GPIOD, GPIO_PinSource13, GPIO_AF_TIM4);
- GPIO_PinAFConfig(GPIOD, GPIO_PinSource14, GPIO_AF_TIM4);
- GPIO_PinAFConfig(GPIOD, GPIO_PinSource15, GPIO_AF_TIM4);

- /* GPIOA Configuration: CH1 (PB4) and CH2 (PB5) */ //設定PB4 5為輸出模式 提供模擬中斷來源
- GPIO_InitStructure2.GPIO_Pin = GPIO_Pin_4 | GPIO_Pin_5 ;
- GPIO_InitStructure2.GPIO_Mode = GPIO_Mode_OUT;            //輸出信號模式
- GPIO_InitStructure2.GPIO_OType = GPIO_OType_PP;
- GPIO_InitStructure2.GPIO_Speed = GPIO_Speed_100MHz;
- GPIO_InitStructure2.GPIO_PuPd = GPIO_PuPd_UP;
- GPIO_Init(GPIOB, &GPIO_InitStructure2);

- /* GPIOA Configuration: (PA2) and (PA3) */     //設定PA2 3為輸入模式 提供接收中斷來源
- GPIO_InitStructure2.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3 ;
- GPIO_InitStructure2.GPIO_Mode = GPIO_Mode_IN;
- GPIO_InitStructure2.GPIO_Speed = GPIO_Speed_100MHz;
- GPIO_InitStructure2.GPIO_OType = GPIO_OType_PP;
- GPIO_InitStructure2.GPIO_PuPd = GPIO_PuPd_DOWN ;
- GPIO_Init(GPIOA, &GPIO_InitStructure2); 
    
- // Setup Blue & Green LED on STM32-Discovery Board to use PWM. / //PD與LED3456相連實作PWM
- GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_12 | GPIO_Pin_13| GPIO_Pin_14| GPIO_Pin_15;
- GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;            // Alt Function - Push Pull
- GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
- GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
- GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
- GPIO_Init( GPIOD, &GPIO_InitStructure );

//=======================================  

//====Interrupt set section==============

- //==清空中斷標誌==
- EXTI_ClearITPendingBit(EXTI_Line2);
- EXTI_ClearITPendingBit(EXTI_Line3);

- //==選擇中斷PIN腳 A2 A3======
- SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource2);
- SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOA, EXTI_PinSource3);
  
- //==  
- EXTI_InitStructure.EXTI_Line = EXTI_Line2  ; //選擇中斷線路2 
- EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt; //設置為中斷請求，非事件請求
- EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling //設置中斷觸發方式為 下降沿觸發
- EXTI_InitStructure.EXTI_LineCmd = ENABLE;            //外部中斷enable
- EXTI_Init(&EXTI_InitStructure);
- EXTI_GenerateSWInterrupt(EXTI_Line2);
    
- EXTI_InitStructure.EXTI_Line = EXTI_Line3 ; //選擇中斷線路3 
- EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt; //设設置為中斷請求，非事件請求
- EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling; //設置中斷觸發方式為 下降沿觸發
- EXTI_InitStructure.EXTI_LineCmd = ENABLE;            //外部中斷enable
- EXTI_Init(&EXTI_InitStructure);
- EXTI_GenerateSWInterrupt(EXTI_Line3);

- //===給予中斷分組與優先權的設定===
- NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);      //選擇中斷分組2
- NVIC_InitStructure.NVIC_IRQChannel = EXTI2_IRQn  ;     //選擇中斷通道2
- NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; //搶占式中斷優先級設置為0
- NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;        //響應式中斷優先級設置為0
- NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;           //enable中断
- NVIC_Init(&NVIC_InitStructure);

- //===Timer section===
- PrescalerValue = (uint16_t) ((SystemCoreClock /4) / 100000) - 1; //算脈衝周期的時間

-//==TIMER 4 設定
- TIM_TimeBaseStructInit( &TIM_TimeBaseInitStruct );
- TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1; 
- TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up; //上數模式
- TIM_TimeBaseInitStruct.TIM_Period = 2000 - 1;   // 0..2000   //周期
- TIM_TimeBaseInitStruct.TIM_Prescaler = PrescalerValue;       
- TIM_TimeBaseInit( TIM4, &TIM_TimeBaseInitStruct );

-//==TIMER 4 CCRx 暫存器設定
- TIM_OCStructInit( &TIM_OCInitStruct );
- TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
- TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
- // Initial duty cycle equals 0%. Value can range from zero to 1000.
- TIM_OCInitStruct.TIM_Pulse = 1000-1; // 0 .. 1000 (0=Always Off, 1000=Always On)

-//==TIMER channel init
- TIM_OC1Init( TIM4, &TIM_OCInitStruct ); // Channel 1  LED
- TIM_OC2Init( TIM4, &TIM_OCInitStruct ); // Channel 2  LED
- TIM_OC3Init( TIM4, &TIM_OCInitStruct ); // Channel 3  LED
- TIM_OC4Init( TIM4, &TIM_OCInitStruct ); // Channel 4  LED
- TIM_Cmd( TIM4, ENABLE );

- TIM4->CCR1 = 500-1;
- TIM4->CCR2 = 500-1;
- TIM4->CCR3 = 500-1;
- TIM4->CCR4 = 500-1;

//=======================================

//====中斷subroutine=====================

void EXTI2_IRQHandler(void) //加長脈波頻寬的中斷subroutine

{
 
 if(EXTI_GetITStatus(EXTI_Line2) != 0)
 
 {
    EXTI_ClearITPendingBit(EXTI_Line2);   
    
    if (brightness <= 1999 - 100)
        brightness +=100;

    TIM4->CCR1 = brightness;

    TIM4->CCR2 = brightness;

    TIM4->CCR3 = brightness;

    TIM4->CCR4 = brightness;
    
    EXTI_ClearITPendingBit(EXTI_Line2);

    EXTI_ClearITPendingBit(EXTI_Line3);
  }
}

void EXTI3_IRQHandler(void)  //減少脈波頻寬的中斷subroutine
{
 
 if(EXTI_GetITStatus(EXTI_Line3) != 0)
 
 {
    EXTI_ClearITPendingBit(EXTI_Line3);
    
    if (brightness >= 199)
        brightness -=100;

    TIM4->CCR1 = brightness;

    TIM4->CCR2 = brightness;

    TIM4->CCR3 = brightness;

    TIM4->CCR4 = brightness;
    
    EXTI_ClearITPendingBit(EXTI_Line2);

    EXTI_ClearITPendingBit(EXTI_Line3);
    }
}

//=======================================

Demo
=============
http://youtu.be/RHzLguvuOKY

http://youtu.be/guG6MdLIwfI

http://youtu.be/jJfebbbMDPw

Reference
=============
http://zh.wikipedia.org/zh-tw/%E8%84%88%E8%A1%9D%E5%AF%AC%E5%BA%A6%E8%AA%BF%E8%AE%8A

http://ppt.cc/nIAF

http://www.google.com.tw/url?sa=t&rct=j&q=pwm&source=web&cd=10&cad=rja&ved=0CFMQFjAJ&url=http%3A%2F%2Fwww.vr.ncue.edu.tw%2Fesa%2Fa1001%2FPWM.pdf&ei=S3OoUO6pOafcmAWWiIGQDw&usg=AFQjCNE_7pw6paGQzH7kSwkwD2witqcC-A

http://hi.baidu.com/snic_k/item/0f045e3288e6683d2e20c42b

陳志旺（2012），STM32 嵌入式微控制器快速上手，中國：電子工業出版社。