版本 556e9e70282c88c0933d4c9cd7f9b1b79e4cf124
Changes from 556e9e70282c88c0933d4c9cd7f9b1b79e4cf124 to a209dee4c0dcef29fabf333e4cdbea1f02836d58
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title: Pulse-Width Modulation(PWM)
title: Pulse-Width Modulation (PWM)
...
Introduction
============
Pulse-Width Modulation, 又稱pulse-duration modulation(PDM)
, 其利用在頻率不變的狀態下, 改變工作週期大小, 使整體平均電壓值上升或下降, 藉此間歇性電壓及功率切換以節省能源及控制等效果.
.. image:: /PWM_intr.PNG
Implementation
==============
PWM需要透過Timer來實現,STM32的Timer可分為以下幾種
- Basic timers 基本定時器(TIM6 和 TIM7)
- 具有 16-bit auto-reload upcounter driven by a programmable prescaler
- 用途: Synchronization circuit to trigger the DAC(內部連接至DAC)
- Advanced-control timers 高級控制定時器(TIM1 和 TIM8)
- 具有 16-bit up, down, up/down auto-reload counter driven by a programmable prescaler which allowing dividing the counter clock frequency either by any factor between 1 and 65536(2^16).
- 用途: Up to 4 independent channels for input capture, output compare, PWM generation(Edge and Center-aligned Mode) and one-pulse mode output.
- General-purpose timers 通用定時器(TIM9 to TIM14)
- 具有16-bit auto-reload up counter.
- 以及16-bit programmable prescaler used to divide the counter clock frequency by any factor between 1 and 65536.
- 用途: Up to 2 independent channels for input capture, output compare, PWM generation(Edge and Center-aligned Mode) and one-pulse mode output.
- General-purpose timers 通用定時器(TIM2 to TIM5)
- 具有16-bit (TIM3 & TIM4) or 32-bit (TIM2 & TIM5) up, down, up/dowm auto-reload counter.
- 以及16-bit programmable prescaler used to divide the counter clock frequency by any factor between 1 and 65536.
- 用途: Up to 4 independent channels for input capture, output compare, PWM generation(Edge and Center-aligned Mode) and one-pulse mode output.
- 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:: /embedded/PWM-Timer_up_mode.bmp
-----------
.. image:: /embedded/PWM-Timer_down_mode.bmp
-----------
.. image:: /embedded/PWM-Timer_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 1 duty cycle(75%)>PWM 2 duty cycle(25%),PWM 1 Mode看起來會比PWM 2 Mode亮。
-----------
Code_section
=============
.. code-block:: prettyprint
//====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
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 set 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)
{
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)
{
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
Demo video
=============
http://youtu.be/RHzLguvuOKY
http://youtu.be/guG6MdLIwfI (LED 3 4 5 6依序 亮-暗 轉換)
http://youtu.be/jJfebbbMDPw (透過外接BUTTON 調整led亮度)
* http://youtu.be/RHzLguvuOKY
* http://youtu.be/guG6MdLIwfI (LED 3 4 5 6依序 亮-暗 轉換)
* http://youtu.be/jJfebbbMDPw (透過外接 BUTTON 調整 LED亮度)
補充
=============
1. PWM較省電?
因為一般類比電壓要降低電壓輸出需靠增加電阻,源頭輸出電壓"持續"都為同一電壓,不過利用電阻改變最後輸出電壓,而PWM他靠的是一段時間內輸出的頻率來模擬類比電壓,"不需要持續的輸出",故不會降電浪費在電阻上,即可達到省電效果。
例如:使用9V電池來給一燈泡供電,連接電池跟燈泡時間為50ms,斷開電池和燈泡時間為50ms。1秒鐘(1000ms)過後,會重複此過程10次,燈泡將會連接到一個4.5V電池(9V電池的50%)上一樣。
2. overflow 和 UEV UIF的關係
UEV occurs everytime an overflow occurs, and UIF is a flag triggered when overflow occurs, if you don't clean the flag, it will remain triggered.
3. 向上計數和向下計數的差別
以四位元向上計數器為例,由四個JK正反器串接而成,輸出DCBA由0000依據二進位的變化至1111。下一個脈波來時,又回到0000。依此類推故此計數器可由0計數到15。而向下計數器與向上計數器不同點是下一級的CLK接於前一級的Q,輸出DCBA由1111向下計數到0000,待下一個時脈輸入時又變為1111,再依序變化。
4. timer 和 RTC的差別
The system timer is what makes everything in the computer run at the same speed.
For example, your CPU won't look for a fresh batch of data while the Memory is still trying to feed it the last batch.The Real Time Clock tells the system what day/time it is.
5. TIM_OCMode (timer output compare mode)
.. image:: /TIM_OCMode.png
6. PWM先高後低和先低後高 在步進馬達上表現有什麼差別?
在馬達剛要啟動時,因為先高後低是在duty cycle的前半段先供電,而先低後高則是到duty cycle的後半段才供電,在馬達的表現上 先高後低的啟動速度會比先低後高還要快一點
7. 改成中央對齊計數方式會怎麼樣?
.. image:: /中央對齊.png
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。
P.155 8.3.3 計數器模式
範例程式
=============
- https://gitcafe.com/embedded2012/P-coolod/blob/master/Lab-6/discoveryF4/TIM_PWM_Output/main.c
此程式為依序更改 LED 3 4 5 6(利用PD12 13 14 15 作PWM應用)亮度 由暗漸漸轉亮 再由亮漸漸轉暗
- https://gitcafe.com/embedded2012/P-coolod/blob/master/Lab-6/discoveryF4/GPIO_test/main.c
此程式碼利用PB4 5作Output pin持續輸出高態電壓,PA2 3作Input Pin接收來在output pin的電壓輸入,並設定負緣觸發中斷,中斷觸發以改變duty cycle佔空比,電壓高低態變化則利用外接button,當按下button則電壓 高->低 ,PA2 3接收到變化便會觸發中斷,透過改變Timer來做duty cycle佔空比的改變,以達到LED亮暗改變.(以下圖說明)
.. image:: /embedded/PWM-GPIO_test_Explain_figure.png