PWM (pulse width modulation) of STM32 notes

Write it at the front ：
The purpose of this article is to summarize backup 、 For future reference , Because it's a personal summary , If there is any wrong , Welcome to correct ; in addition , Most of the content comes from the Internet 、 Books 、 And all kinds of manuals , In case of infringement, please inform , Immediately delete the post and apologize .

 

Catalog

One 、PWM brief introduction

Two 、STM32F1 Chinese vs PWM Support for

3、 ... and 、PWM Count mode

Four 、 working principle

5、 ... and 、PWM Output mode

6、 ... and 、 And PWM Regulation related functions

7、 ... and 、 Routine demonstration

8、 ... and 、 other

---

 

One 、PWM brief introduction

Pulse width modulation （ English ：Pulse Width Modulation, abbreviation ：PWM）, abbreviation Pulse width modulation , It is a technology that converts analog signals into pulses , Generally, the period of the converted pulse is fixed , But the working period of the pulse will change according to the size of the analog signal .

Usually we use it a lot PWM Technology is used to adjust light or speed , This is also the most common .

 

Two 、STM32F1 Chinese vs PWM Support for

stay STM32F1 Inside ,PWM The generation of is by Timer Output , But not all of them Timer All support ; Be careful , What we are talking about here is the use of hardware technology to produce PWM, It produces PWM The frequency is very considerable , As for software timing control IO Output pin , The so-called software PWM technology , I won't elaborate here .

Learn from the above ,STM32F1 Of Timer Can produce PWM Of , But not all of them Timer All support ; therefore , Look through the manual , It can be learned that , Support PWM Hardware output technology Timer Yes “ Universal timer ” and “ Advanced control timing ” These two types , And for “ Basic timer ” No PWM Hardware output technology , So we should pay a little attention in practical application , So as not to cause unreasonable resource allocation .

1、 Universal timer （TIM2 ~ TIM5）

Every time there is 4 Independent channels as output ：

2、 Advanced control timer （TIM1 & TIM8）

This timer can generate 7 road PWM Output ：

3、 Basic timer （TIM6 & TIM7）

Explanation of timer , You can read the previous chapter ：STM32 Note it Timer（ Timer ）

 

3、 ... and 、PWM Count mode

• Edge alignment mode

1、 Count up

2、 Count down

• Center alignment mode

 

Four 、 working principle

Take counting up as an example ：

The count value is fixed from... Per cycle Bottom Start counting , I've been tired Top, Then count again ; As long as it doesn't stop running , So it goes back and forth ; from Bottom Add up to Top For a cycle , In order to make PWM pulse , And all we have to do is set up Compare Value , thus , Just one more Compare reference value , It can also be called split value ; When counting , Count every time you accumulate , All follow  Compare Comparison of values , When the count value is equal to Compare Value at the same time , The control output state is the opposite , So as to get the Output Plot line of .

 

5、 ... and 、PWM Output mode

above-mentioned ,Compare Comparison of values , When the count value is equal to Compare Value at the same time , The control output state is the opposite ; therefore , There will be two duty cycle states , One is when the figure above Compare To Top The output is high level , The other is the opposite Bottom to Compare High level between .

So that corresponds to STM32 in , Its status is determined in  TIMx_CCMRx Register bit 6:4 Of  OCxM[2:0] in ：

Be careful ：STM32 Medium PWM The mode just distinguishes when the active level is , However, it is not determined whether the high level is active or the low level is active . This needs to be combined CCER The register of CCxP Bit to determine .

 

6、 ... and 、 And PWM Regulation related functions

function	function
void TIM_SetClockDivision(TIM_TypeDef* TIMx, uint16_t TIM_CKD)	Clock division factor setting
void TIM_PrescalerConfig(TIM_TypeDef* TIMx, uint16_t Prescaler, uint16_t TIM_PSCReloadMode)	TIM_x Prescaler setting
void TIM_SetAutoreload(TIM_TypeDef* TIMx, uint16_t Autoreload)	Set the automatic loading cycle of the timer
void TIM_SetCompare1(TIM_TypeDef* TIMx, uint16_t Compare1)	Set the comparison value of each channel （ It can be understood as duty cycle ）
void TIM_SetCompare2(TIM_TypeDef* TIMx, uint16_t Compare2)
void TIM_SetCompare3(TIM_TypeDef* TIMx, uint16_t Compare3)
void TIM_SetCompare4(TIM_TypeDef* TIMx, uint16_t Compare4)

Generally speaking , Calculate what you need PWM frequency = System clock / Clock division factor / TIM_x prescale / Automatic loading cycle .

 

7、 ... and 、 Routine demonstration

Let's say TIM3 Of ch3、4 As an example ：

#define TIME3_ARR			624			//  Automatic reload register cycle value 
#define TIME3_PSC			71			// TIMx Clock frequency prescaled value 
#define TIME3_PULSE			(uint16_t)((TIME3_ARR+1) / 2 - 1)		//  Compare register values 

#define TIME3_CH3_PIN       GPIO_Pin_0
#define TIME3_CH4_PIN       GPIO_Pin_1

uint16_t Time3_CCR3_Val = TIME3_PULSE;
uint16_t Time3_CCR4_Val = TIME3_PULSE;

void TIM3_PWM_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
    TIM_OCInitTypeDef  TIM_OCInitStructure;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB | RCC_APB2Periph_AFIO, ENABLE);
    GPIO_InitStructure.GPIO_Pin = TIME3_CH3_PIN | TIME3_CH4_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOB, &GPIO_InitStructure);				// IO Mouth configuration 

    /* Time base configuration */
    TIM_TimeBaseStructure.TIM_Period = TIME3_ARR;
    TIM_TimeBaseStructure.TIM_Prescaler = TIME3_PSC;	// 1600Hz
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;        //  Clock division factor 
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);		//  Basic configuration of timer 

    /* PWM1 Mode configuration: Channel3 */
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;   // PWM mode 1
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStructure.TIM_Pulse = Time3_CCR3_Val;     //  Duty cycle setting 
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;    //  Polarity is high 

    TIM_OC3Init(TIM3, &TIM_OCInitStructure);

    TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Enable);

    /* PWM1 Mode configuration: Channel4 */
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStructure.TIM_Pulse = Time3_CCR4_Val;

    TIM_OC4Init(TIM3, &TIM_OCInitStructure);

    TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Enable); //  Enable pre loading （ Can make  CCR4 Preload of ）

    TIM_ARRPreloadConfig(TIM3, ENABLE); //  Enable automatic reloading of registers  ARR Preload of 

    /* TIM3 enable counter */
    TIM_Cmd(TIM3, ENABLE);
}

ad locum , Pay attention to  TIM_ARRPreloadConfig() function , Its function is only to allow or prohibit the timer to ARR Whether to update immediately after writing the new value in the buffer of , The operation is TIMx->CR1 Medium “APRE” position , Its bit is explained as follows ：

We can't get any useful information from the above explanation , You need to combine the following two examples to understand ：

chart 1：APRE = 0（ The default value is ）, When ARR When the value is modified , At the same time, update the value of shadow register immediately

You can see that the previous parameter is ARR = FF, When ARR Reassign to zero 36 after , It will take effect immediately , And is equal to 36 Overflow occurred at , And generate an event .

chart 2：APRE = 1, When ARR When the value is modified , It has to be in the next event UEV The value of the shadow register cannot be updated until it occurs

You can see here that the previous parameter is ARR = F5, When to modify ARR The value of is 36, Only the reload register value of the surface has changed , But the shadow register that really works doesn't change . At this time, you need to wait until the end of the previous cycle , An update event occurred , The shadow register will be modified .

And in the program ,TIM_ARRPreloadConfig(TIM3, ENABLE); So that when we change the value , Avoid triggering events that do not conform to the parameters before and after modification during switching （ In the picture above 2 For example , If it is not enabled APRE, So here you are ARR Reassign to zero 36 after , The data will take effect immediately ; Because we were counting at that time  F1 It was modified when , meanwhile , because APRE = 0, So when we count to F5 It will not generate an event and reset the count value （ At this time, the trigger value becomes 36 了 ）, Will run until 0xFFFF（ With 16bit Take the timer as an example ） Then the register overflows again 0 Start counting , Finally, I counted to 36 An event occurs when , Then it will cause , The total count during this switch is ： 0xFFFF - 0x00F5 + 36; If in PWM In mode , In this way, it becomes writing new  ARR When the value of , It is possible to generate a high when switching （ low ） Irregular pulses of level （ It does not conform to the requirements before and after modification ））.

alike , about  TIM_OCxPreloadConfig() The same goes for functions .

 

8、 ... and 、 other

1、 It is worth noting that , Using advanced timer TIM8 When （ Maybe other advanced timers need to be added , But in TIM1 Has been opened by default ）, Need to add again  TIM_CtrlPWMOutputs(TIM8, ENABLE); Execute the function to output PWM wave . in the light of  TIM_CtrlPWMOutputs function , See the following instructions ：

/**
  * @brief  Enables or disables the TIM peripheral Main Outputs.
  * @param  TIMx: where x can be 1, 8, 15, 16 or 17 to select the TIMx peripheral.
  * @param  NewState: new state of the TIM peripheral Main Outputs.
  *   This parameter can be: ENABLE or DISABLE.
  * @retval None
  */
void TIM_CtrlPWMOutputs(TIM_TypeDef* TIMx, FunctionalState NewState);

2、 For using Keil Software simulation , Use the built-in logic analyzer to see the waveform , You have to set the clock frequency ：

Then you need to set it here （ Remember to go back to your chip ）：

And then go into DEBUG Pattern , Set up PWM Output port （ There is a random one here ）：

Last , The key is coming. ：Keil Software waveform simulation , Relatively a little unreliable , Do not use this if you can observe with an oscilloscope , Or get a logic analyzer , also , As if Keil Does not support TIM5 Observe the above timer output .