In this paper , Xiaobian mainly introduces how to use general timer to generate PWM Output .

One 、 Introduction of general timer

     The universal timer is driven by a programmable prescaler 16 Bit auto loading counter . It is suitable for many occasions , Including measuring the pulse length of the input signal ( Input acquisition ) Or produce an output waveform ( Output comparison and PWM). When using timer prescaler and RCC Clock controller prescaler time , Pulse length and waveform period can be adjusted from a few microseconds to a few milliseconds .

Two 、 Function of general timer

Universal TIMx (TIM2、 TIM3、 TIM4 and TIM5) Timer functions include ：
■ 16 Position up 、 Down 、 Up / Auto load counter down .
■ 16 Bit programmable ( It can be modified in real time ) Preassigned frequency counter .
■ 4 A separate channel ：
    ◆ Input capture ◆ Output comparison ◆ PWM Generate ◆ Monopulse mode output
■ Use external signal to control timer and timer interconnection synchronization circuit .
■ Interrupt occurs when the following events occur /DMA：
    ◆ to update ：◆ Triggering event ◆ Input capture ◆ Output comparison
■ Support for incremental positioning ( orthogonal ) Encoder and Hall sensor circuits .
■ Trigger input as an external clock or current management by cycle .

3、 ... and 、PWM Introduction to

    PWM Control is pulse width modulation technology , By modulating the width of a series of pulses , To equivalently obtain the required waveform （ Including shape and amplitude ）, PWM Control technology is most widely used in inverter circuit , Most of the applied inverter circuits are PWM type , It is widely used in measurement 、 Communication to many fields of power control and conversion .

Four 、PWM Implementation method

     Realization PWM There are mainly traditional digital circuits 、 Microcontroller common I/O Analog and microcontroller PWM Direct output, etc .
■ Traditional digital circuit ： Realize with traditional digital circuit PWM（ Such as 555 Timer ）.
■ Microcontroller common I/O Simulation mode ： For microcontrollers, there is no PWM Output function （ Such as 51 Single chip microcomputer ）, Can pass CPU The control is ordinary I/O Mouth to achieve PWM Output .
■ Micro controller PWM Direct output mode ： Those who have PWM Microcontroller with output function , After simple configuration, it can be output on the designated pin of the microcontroller PWM pulse .

5、 ... and 、 Example

     One day , Xiao Ming suddenly wants to do a project based on STM32F103ZE On the development board LED6、LED7 The breathing lamp of , So how do you do that ？ Now let's see the implementation method of Xiaobian .

1、 Module analysis

     In Xiao Ming's breathing lamp project , We don't need many modules , Only use LED Module and general timer module are enough . utilize LED The module can control LED Light status , Use the general timer module to use LED Module change LED The state of the light .

2、 Implementation code

（1） The main function

int main(void)
{
    
	u8 flag = 1;
	u32 count = 0;
	TIM3_PWMInit();
	while(1){
    
		dealy_ms(10);
		if(flag==1)		{
    
			count++;
			if(count>300)	flag=0;				
		}else{
    
			count--;
			if(count==0)   flag=1;			
		}
		//TIM_SetCompare1 The parameters of the function 2 Duty  take TIM3 The time period of is divided into two parts , stay Duty Before the time of Duty After time, the high and low levels of the two parts are different 
		TIM_SetCompare1(TIM3,count);// Set up TIMx Capture comparison 1 Register values  
		TIM_SetCompare2(TIM3,count);// Set up TIMx Capture comparison 2 Register values  
	}	
}

（2）、 General timer function

/* * @brif intialization of generic Timer3 which is used to PAM( Initialization is used for PWM General timer timer 3) * @para none * @reval none */
void TIM3_PWMInit(void)
{
    
	/*  Define initialization variables  */
	GPIO_InitTypeDef GPIO_InitStructure;   // Declare a structure variable , Used to initialize GPIO
	TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;// Declare a structure variable , Used to initialize the timer 
	TIM_OCInitTypeDef TIM_OCInitStructure;// according to TIM_OCInitStruct The parameter specified in TIMx

	/*  Turn on the clock  */
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC,ENABLE);
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO,ENABLE);

	/*  To configure GPIO Mode and IO mouth  */
	GPIO_InitStructure.GPIO_Pin=GPIO_Pin_6|GPIO_Pin_7;// Choose LED The pin of 
	GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;// Set up LED The frequency of 
	GPIO_InitStructure.GPIO_Mode=GPIO_Mode_AF_PP;// Multiplexing push pull output 
	GPIO_Init(GPIOC,&GPIO_InitStructure);

	//TIM3 Timer initialization   Adopt no frequency division  PWM  frequency =72000/900=8Khz
	TIM_TimeBaseInitStructure.TIM_Period = 900-1;	   // Set the value of the automatic reload register cycle 
	TIM_TimeBaseInitStructure.TIM_Prescaler = 1-1;// Set as TIMx Clock frequency prescaled value , Here the frequency division coefficient is 1,  No frequency division 
	TIM_TimeBaseInitStructure.TIM_ClockDivision = 0;// Set the clock split :TDTS = Tck_tim
	TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;	//TIM Upcount mode 
	TIM_TimeBaseInit(TIM3, & TIM_TimeBaseInitStructure);

	GPIO_PinRemapConfig(GPIO_FullRemap_TIM3,ENABLE);// Change the mapping of the specified pin   Here we choose complete remapping 

	//PWM initialization   according to TIM_OCInitStruct The parameter specified in TIMx
	TIM_OCInitStructure.TIM_OCMode=TIM_OCMode_PWM1;// Set up PWM The output mode of 
	TIM_OCInitStructure.TIM_OutputState=TIM_OutputState_Enable;//PWM Output enable 
	TIM_OCInitStructure.TIM_OCPolarity=TIM_OCPolarity_Low;// Set the timer to TIM  The output is less polar 
	TIM_OC1Init(TIM3,&TIM_OCInitStructure);// Initial swap capture / Compare register  1
	TIM_OC2Init(TIM3,&TIM_OCInitStructure);// Initialize capture / Compare register  2
	TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);// To enable or disable TIMx stay CCR1 Pre loaded registers on 
	TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Enable);// To enable or disable TIMx stay CCR2 Pre loaded registers on 
	
	TIM_Cmd(TIM3,ENABLE);// To enable or disable TIMx peripherals 
}

6、 ... and 、 summary

     In Xiao Ming's breathing lamp project , Because of the general timer 3 And PC6、PC7 There is a remapping relationship , therefore , We only need to initialize the pin in the process of using , Don't deliberately control LED The light goes on and off .LED The light turns on and off with a general timer TIM3 adopt PWM Mode output .