当前位置：网站首页>Learning record: how to perform PWM output

Pulse width modulation (PWM),“Pulse Width Modulation” Abbreviation , abbreviation Pulse width modulation , It is a very effective technology to control analog circuit by using digital output of microprocessor . A little bit more simple , It's the control of pulse width .

and PWM Output is External output pulse width （ The duty cycle ） Adjustable square wave signal , The signal frequency is determined by the auto reload register ARR Value determination of , The duty cycle is determined by the comparison register CCR Value determination of .

STM32 In addition to TIM6、7. Other timers can be used to generate PWM Output . One of the advanced timers TIM1、TIM8 It can produce as many as 7 On the road PWM Output . And universal timers can also generate up to 4 On the road PWM Output , such ,STM32 At most... Can be generated at the same time 30 road PWM Output .

1.1、PWM The output mode — classification

PWM There are two patterns ,PWM1 and PWM2;

With PWM1 Pattern , Counter CNT The counting direction is also divided into edge alignment mode and center alignment mode .PWM The signal It is mainly used to control the motor , One General motor control uses edge alignment mode ,FOC The motor generally uses the center alignment mode .

Edge alignment when ,CNT Only work in increasing or decreasing . When the center is aligned ,CNT Work is increasing and decreasing .

1.2、PWM Edge alignment mode

In incremental count mode , Counter from 0 Count to auto overload value （TIMx_ARR The contents of the register ）, And then again from 0 Start counting and generate counter overflow Events .

In edge alignment mode , Counter CNT Working in only one mode , Increasing or decreasing mode . With CNT Working in incremental mode, for example , In the middle ARR=8,CCR=4,CNT from 0 Start counting , When CNT<CCR The value of ,OCxREF For effective high level , At the same time , Compare interrupt registers CCxIF Set up . When CCR=CNT≤ARR when ,OCxREF Invalid low level . then CNT Again from 0 Start counting and generate counter overflow Events , And so on .

1.3、PWM Center alignment mode

In center alignment mode , Counter CNT It's a job to do / In decreasing mode . At the beginning , Counter CNT from 0 Start counting to the auto reload value minus 1(ARR-1), Generate counter overflow event ; Then count down from the auto overload value to 1 And generate counter underflow event . After from 0 Start counting again .

chart PWM1 The center of the pattern aligns the waveform yes PWM1 The center of the pattern aligns the waveform ,ARR=8,CCR=4.

The first stage counter CNT Working in incremental mode , from 0 Start counting , When CNT<CCR when ,OCxREF For effective high level , When CCR≤CNT<<ARR when ,OCxREF Invalid low level .

The second stage counter CNT Working in decrement mode , from ARR The value of begins to decrease , When CNT>CCR when ,OCxREF Is invalid low level , When CCR≥CNT≥1 when ,OCxREF For effective high level .

On the waveform, we divide the waveform into two stages ：

The first stage is the counter CNT Waveforms working in incremental mode , This stage is divided into ① and ② Two phases ;

The second stage is the counter CNT Waveforms working in decreasing mode , This stage is divided into ③ and ④ Two phases .

The waveform characteristics in the center alignment mode are ① and ③ rank The period of time is equal ,② and ④ The stages are equal in time .

Center alignment patterns are divided into center alignment patterns 1、2、3, Three ： Specifically, the register CR1 position CMS[1:0] To configure .

The difference is to compare the interrupt flag bit CCxIF When to place 1： Central mode 1 stay CNT Set... When decrementing the count 1, Center alignment mode 2 stay CNT Set... When counting up 1, Central mode 3 stay CNT Set... When counting up and down 1.

Two 、PWM working process

2.1、 Channel 1 output working process

CCR1: Capture comparison ( value ) register （x=1,2,3,4): Set the comparison value .

CCMR1: OC1M[2:0] position ：

about PWM Under way , Used for setting up PWM Pattern 1【110】 perhaps PWM Pattern 2【111】

CCER:CC1P position ： Input / Capture 1 Output polarity .0： High active ,1： Low level active .

CCER:CC1E position ： Input / Capture 1 Output enable .0： close ,1： open .

3、 ... and 、PWM Register configuration

Capture / Compare mode register （TIMx_CCMR1/2）、 Capture / Compare enable register （TIMx_CCER）、 Capture / Compare register （TIMx_CCR1~4）.

3.1、 Capture / Compare mode register （TIMx_CCMR1/2）

The registers are TIMx _CCMR1 and TIMx _CCMR2.TIMx_CCMR1 control CH1 and 2, and TIMx_CCMR2 control CH3 and 4.

Some bits of this register are in different modes , Function differently , So in the picture 14.4.8 in , We divided the registers 2 layer , The upper layer corresponds to output and the lower layer corresponds to input .

Mode setting bit OCxM, This part is made up of 3 A composition . A total of... Can be configured 7 Patterns , We use PWM Pattern , So this 3 Bit must be set to 110/111. These two kinds of PWM The difference between modes is that the polarity of the output level is opposite .

3.2、 Capture / Compare enable register （TIMx_CCER）

This register controls the switch of each input and output channel .

It's just... Here CC2E position , This bit is an input / Capture 2 Output enable bit , If you want to PWM from IO output , This bit must be set to 1, So we need to set this bit to 1.

3.3、 Capture / Compare register （TIMx_CCR1~4）

This register has 4 individual , Corresponding 4 Two transmission channels CH1~4; this 4 Each register is about the same .

In output mode , The value of this register is the same as CNT Value comparison of , Generate corresponding actions according to the comparison results . Take advantage of this , By modifying the value of this register , You can control PWM The output pulse width of .

Four 、 Remapping function

utilize TIM3 Of CH2 Output PWM To control DS0 The brightness of , however TIM3_CH2 The default is connected to PA7 above , And ours DS0 Connect to PB5 above , If it's normal MCU, Maybe you can only use the fly wire handle PA7 Fly to PB5 Come up and realize . however STM32, You can use the remapping function , hold TIM3_CH2 Mapping to PB5 On .

STM32 The remapping control of is by reusing remapping and debugging IO Configuration register （AFIO_MAPR） The control of the

TIM3_REMAP By [11:10] this 2 Bit controlled ;

By default ,TIM3_REMAP[1:0] by 00, There is no remapping , therefore TIM3_CH1~TIM3_CH4 They are connected to PA6、PA7、PB0 and PB1 Upper , And we want TIM3_CH2 Mapping to PB5 On , You need to set TIM3_REMAP[1:0]=10, That is, partial remapping , Here we need to pay attention to , here TIM3_CH1 Also mapped to PB4 Yes .

5、 ... and 、 Programming

The output step ：

1. Enable timer 3 And the related IO Port clock .

Enable timer 3 The clock ：RCC_APB1PeriphClockCmd();

Can make GPIOB The clock ：RCC_APB2PeriphClockCmd();

2. initialization IO The port is the output of multiplexing function . function ：GPIO_Init();

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

3. Here we are going to PB5 Used as a timer PWM Output pin , So remap the configuration ,

So it needs to be turned on AFIO The clock . Set remapping at the same time .

RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);

GPIO_PinRemapConfig(GPIO_PartialRemap_TIM3, ENABLE);

4. Initialize the timer ：ARR,PSC etc. ：TIM_TimeBaseInit();

5. Initialize the output comparison parameters :TIM_OC2Init();

6. Enable preload register ： TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);

7. Enable timer .TIM_Cmd();

8. Constantly changing the comparison value CCRx, Achieve different duty cycle effects :TIM_SetCompare2();

Programming :

time.c file

#include "timer.h"
#include "led.h"
#include "usart.h"

/*
1, increase TIM3_PWM_Init function .
2, increase LED0_PWM_VAL Macro definition , control TIM3_CH2 Pulse width 									  
*/ 
/*  	  
 Universal timer 3 Interrupt initialization 
 Here, the clock is selected as APB1 Of 2 times , and APB1 by 36M
arr： Auto reload value .
psc： Clock presplitting frequency 
 Here's a timer 3!
*/

void TIM3_Int_Init(u16 arr,u16 psc)
{
		TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
		NVIC_InitTypeDef NVIC_InitStructure;

		RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE); // Clock enable 

		TIM_TimeBaseStructure.TIM_Period = arr; // Set the value of the auto reload register cycle for the next update event load activity 	  Count to 5000 by 500ms
		TIM_TimeBaseStructure.TIM_Prescaler =psc; // Set as TIMx Prescaled value of clock frequency divisor   10Khz The counting frequency of   
		TIM_TimeBaseStructure.TIM_ClockDivision = 0; // Set the clock split :TDTS = Tck_tim
		TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM Upcount mode 
		TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); // according to TIM_TimeBaseInitStruct The parameter specified in TIMx Unit of time base 
 
		TIM_ITConfig(TIM3,TIM_IT_Update,ENABLE ); // Enable to designate TIM3 interrupt , Allow update interrupt 

		NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;  //TIM3 interrupt 
		NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;  // Take precedence 0 level 
		NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3;  // From the priority 3 level 
		NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ The channel is energized 
		NVIC_Init(&NVIC_InitStructure);  // according to NVIC_InitStruct The parameter specified in NVIC register 

		TIM_Cmd(TIM3, ENABLE);  // Can make TIMx peripherals 
							 
}

/* Timer 3 Interrupt service routine */
void TIM3_IRQHandler(void)   //TIM3 interrupt 
{
		if (TIM_GetITStatus(TIM3, TIM_IT_Update) != RESET) // Check the specified TIM Whether the interruption occurs or not :TIM  Interrupt source  
		{
			TIM_ClearITPendingBit(TIM3, TIM_IT_Update  );  // eliminate TIMx Interrupt pending bit of :TIM  Interrupt source  
			LED1=!LED1;
		}
}
/*
TIM3 PWM Partial initialization  
PWM Output initialization 
arr： Auto reload value 
psc： Clock presplitting frequency 
*/
void TIM3_PWM_Init(u16 arr,u16 psc)
{  
		GPIO_InitTypeDef GPIO_InitStructure;
		TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;
		TIM_OCInitTypeDef  TIM_OCInitStructure;
	

		RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);	// Enable timer 3 The clock 
		RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB  | RCC_APB2Periph_AFIO, ENABLE);  // Can make GPIO Peripherals and AFIO Multiplexing function module clock 
	
		GPIO_PinRemapConfig(GPIO_PartialRemap_TIM3, ENABLE); //Timer3 Partial remapping   TIM3_CH2->PB5    
 
    // Set this pin to multiplex output function , Output TIM3 CH2 Of PWM Pulse shape 	GPIOB.5
		GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5; //TIM_CH2
		GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  // Multiplexing push pull output 
		GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
		GPIO_Init(GPIOB, &GPIO_InitStructure);// initialization GPIO
 
    // initialization TIM3
		TIM_TimeBaseStructure.TIM_Period = arr; // Set the value of the auto reload register cycle for the next update event load activity 
		TIM_TimeBaseStructure.TIM_Prescaler =psc; // Set as TIMx Prescaled value of clock frequency divisor  
		TIM_TimeBaseStructure.TIM_ClockDivision = 0; // Set the clock split :TDTS = Tck_tim
		TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  //TIM Upcount mode 
		TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure); // according to TIM_TimeBaseInitStruct The parameter specified in TIMx Unit of time base 
	
	  // initialization TIM3 Channel2 PWM Pattern 	 
		TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2; // Select timer mode :TIM Pulse width modulation mode 2
		TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable; // Compare output enable 
		TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High; // Output polarity :TIM High output polarity 
		TIM_OC2Init(TIM3, &TIM_OCInitStructure);  // according to T The specified parameter initializes the peripheral TIM3 OC2

		TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);  // Can make TIM3 stay CCR2 Pre loaded registers on 
 
		TIM_Cmd(TIM3, ENABLE);  // Can make TIM3
}

timer.h The procedure is as follows ：

#ifndef __TIMER_H
#define __TIMER_H
#include "sys.h"

void TIM3_Int_Init(u16 arr,u16 psc);
void TIM3_PWM_Init(u16 arr,u16 psc);
#endif

#include "led.h"
#include "delay.h"
#include "key.h"
#include "sys.h"
#include "usart.h"
#include "timer.h"
 
 int main(void)
 {		
		u16 led0pwmval=0;
		u8 dir=1;	
		delay_init();	    	 // Delay function initialization 	  
		NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2); 	 // Set up NVIC Interrupt grouping 2:2 Bit preemption priority ,2 Bit response priority 
		uart_init(115200);	 // The serial port is initialized to 115200
		LED_Init();			     //LED Port initialization 
		TIM3_PWM_Init(899,0);	 // Regardless of the frequency .PWM frequency =72000000/900=80Khz
   	while(1)
		{
			delay_ms(10);	 
			if(dir)led0pwmval++;
			else led0pwmval--;

			if(led0pwmval>300)dir=0;
			if(led0pwmval==0)dir=1;										 
			TIM_SetCompare2(TIM3,led0pwmval);		   
		}	 
 }

原网站

版权声明
本文为[Bitter tea seeds]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/187/202207060919234706.html