STM32 PWM output and Keil software simulation

STM32 PWM output

Pulse width mode (PWM mode) can be used to generate a signal with a frequency determined by the TIMx_ARR register and a duty cycle determined by the TIMx_CCRx register. In STM32 development, the official library functions provide a relatively complete set of functions, making our development work quite easy. We can even complete our development work and achieve the functions we need without knowing too much about the hardware structure. Here, the author also recommends that you try to familiarize yourself with the functions provided in the firmware library to adjust the frequency and duty cycle of PWM when you are just starting out, and minimize the operation of the underlying registers.

This article uses the STM32F103RB chip, and the output channel is the TIM2_CH2 channel. STM32 has strong portability. If the reader's chip type is different from mine, you can make appropriate modifications to complete your own development.

The library functions used are: 

stm32f10x.h: used for system initialization. No matter what development you do, this library must include 

stm32f10x_tim.h: TIM timer library function 

stm32f10x_rcc.h: clock configuration library function 

stm32f10x_gpio.h: GPIO configuration library functions

From the above library functions, we can see that the contents we need to initialize include TIM2 timer, clock enable configuration, and GPIO enable configuration.

void RCC_Config(void);

void GPIO_Config(void);

void TIM_Config(void);

The next step is to write the function body of each function. In these contents, the official has actually given examples. We configure them according to the official function library, and then modify some official variable properties.

RCC_Config function body

void RCC_Config(void)

{

        // Enable GPIOA, TIM2

        RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);

        RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);

}

GPIO_Config function body

void GPIO_Config(void)

{

//GPIO configuration, the official library gives some parameters that need to be configured. If you forget, just refer to it. I configure GPIOA_Pin_1 here.

        GPIO_InitTypeDef GPIO_InitStructure;

        GPIO_InitStructure.GPIO_Pin=GPIO_Pin_1;

        GPIO_InitStructure.GPIO_Mode=GPIO_Mode_AF_PP;

        GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;

        GPIO_Init(GPIOA,&GPIO_InitStructure);

}

TIM_Config function body 

Before configuring the function body, first understand how the duty cycle and frequency of stm32 are calculated 

①Frequency: The APB1 clock source we use is 72MHz. We do not do frequency division here. We set the input frequency by configuring related parameters. The calculation method is: Input frequency = APB1 clock / (pre-division coefficient + 1) = 72000000Hz / 360 = 200000Hz 

②The TIM_TImeBaseStructure.TIM_Period parameter determines the frequency of the output PWM waveform. The frequency of the output PWM waveform = the input frequency of the timer / TIM_TImeBaseStructure.TIM_Period. In this example, 20000Hz/100=200Hz, that is, one cycle of 5ms 

③Configure the duty cycle: Duty cycle = configured duty cycle value / TIM_TImeBaseStructure.TIM_Period. Use this calculation to determine the duty cycle. In this case, the duty cycle is 50/100=50% 

④Timer enable

void TIM_Config(void)

{

        TIM_TimeBaseInitTypeDef TIM_TImeBaseStructure;

        TIM_OCInitTypeDef  TIM_OCInitStructure;

    //Configure the clock output frequency of TIM2 and initialize other related parameters

        TIM_TImeBaseStructure.TIM_Prescaler=360-1; //Set the frequency of PWM

        TIM_TImeBaseStructure.TIM_CounterMode=0;

        TIM_TImeBaseStructure.TIM_Period=100;

        TIM_TimeBaseInit(TIM2,&TIM_TImeBaseStructure);

    //Set the PWM output mode

        TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM2;

        TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;

        TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable;

        TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;

        TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High;

        TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;

        TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;   

    //Configure the duty cycle

        TIM_OCInitStructure.TIM_Pulse=50;

        TIM_OC2Init(TIM2,&TIM_OCInitStructure);

        TIM_ForcedOC1Config(TIM2,TIM_ForcedAction_Active);

        TIM_Cmd(TIM2,ENABLE);

        TIM_CtrlPWMOutputs(TIM2,ENABLE);

}

Thus, our entire PWM configuration is completed 

Main function

int main()

{

        RCC_Config();

        GPIO_Config();

        TIM_Config();

        while(1)

        {

                ;

        }

}

Next, let's look at the output frequency and waveform of our GPIOA_Pin_1 pin in Keil.

Keil software simulation

①Configure debugging tools 

② Turn on debugging, and set and test the GPIO output pins 

 

③Run at full speed and observe the oscilloscope 
 

STM32-PWM output source code download address  
STM32 firmware library version 3.5 user manual Chinese translation version