Using STM32 HAL and register-level methods

 Generating PWM (Pulse Width Modulation) on an STM32 microcontroller involves configuring a timer (TIM) peripheral to produce a variable-duty-cycle signal. Below is a step-by-step guide using STM32 HAL and register-level methods.

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1. PWM Generation Using STM32 HAL (CubeMX)

(A) CubeMX Setup

1. Enable Timer (e.g., TIM1, TIM2, etc.) in PWM mode.

2. Configure Channel (e.g., CH1, CH2) as PWM Generation.

3. Set:

   • Prescaler (PSC) – Divides the timer clock.

   • Auto-Reload Register (ARR) – Sets PWM frequency.

   • Pulse (CCR) – Sets duty cycle.

(B) Code Implementation

c

#include "stm32f4xx_hal.h"

TIM_HandleTypeDef htim2;

void PWM_Init() {
  TIM_OC_InitTypeDef sConfigOC = {0};

  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 84 - 1;       // PSC = 84 → 1 MHz clock (if APB1 = 84 MHz)
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 1000 - 1;        // ARR = 1000 → 1 kHz PWM
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  HAL_TIM_PWM_Init(&htim2);

  sConfigOC.OCMode = TIM_OCMODE_PWM1;
  sConfigOC.Pulse = 500;               // 50% duty (500/1000)
  sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
  sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
  HAL_TIM_PWM_ConfigChannel(&htim2, &sConfigOC, TIM_CHANNEL_1);

  HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);  // Start PWM
}

int main() {
  HAL_Init();
  SystemClock_Config();  // Ensure clock is configured (e.g., APB1 = 84 MHz)
  PWM_Init();

  while (1) {
    // Adjust duty cycle dynamically
    __HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, 750);  // 75% duty
    HAL_Delay(1000);
    __HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, 250);  // 25% duty
    HAL_Delay(1000);
  }
}

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2. Register-Level PWM Setup (No HAL)

For better performance, configure registers directly:

c

void PWM_Init_Registers() {
  // Enable TIM2 clock (APB1)
  RCC->APB1ENR |= RCC_APB1ENR_TIM2EN;

  // Configure TIM2 for PWM
  TIM2->PSC = 84 - 1;      // Prescaler → 1 MHz clock
  TIM2->ARR = 1000 - 1;    // Auto-reload → 1 kHz frequency
  TIM2->CCR1 = 500;        // 50% duty cycle (CCR1 = Channel 1)

  // PWM Mode 1 (OC1M = 110)
  TIM2->CCMR1 |= TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1;
  TIM2->CCER |= TIM_CCER_CC1E;      // Enable output
  TIM2->CR1 |= TIM_CR1_CEN;         // Start timer
}

int main() {
  PWM_Init_Registers();

  while (1) {
    TIM2->CCR1 = 750;  // 75% duty
    for (volatile int i = 0; i < 1000000; i++);
    TIM2->CCR1 = 250;  // 25% duty
    for (volatile int i = 0; i < 1000000; i++);
  }
}

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3. Key Formulas

(A) PWM Frequency

$$f_{PWM}=\frac{f_{TIM}}{(PSC+1)\times (ARR+1)}$$

• Example:

  • $f_{TIM}=84\text{ MHz}$ (APB1 clock)

  • $PSC=84-1$ → Timer clock = $1\text{ MHz}$

  • $ARR=1000-1$ → $f_{PWM}=\frac{1\text{ MHz}}{1000}=1\text{ kHz}$

(B) Duty Cycle

$$\text{Duty Cycle (\%)}=\left(\frac{CCR}{ARR+1}\right)\times 100$$

• Example:

  • $CCR=500$, $ARR=999$ → 50% duty

  • $CCR=750$ → 75% duty

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4. Applications

• Motor Control (DC, Servo, BLDC)

• LED Dimming

• Audio Generation (Class D Amplifiers)

• Power Converters (Buck/Boost)

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5. Debugging Tips

• Check Clock Settings: Ensure APB1/APB2 clocks are correct.

• Use Logic Analyzer: Verify PWM frequency/duty cycle.

• Adjust Dead Time (for complementary PWM in advanced timers like TIM1).

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Summary Table

Parameter	Role	Example Values
PSC	Divides input clock	84-1 (for 1 MHz)
ARR	Sets PWM period (frequency)	1000-1 → 1 kHz
CCR	Sets duty cycle	500 → 50% duty
OC Mode	PWM mode (1 or 2)	TIM_OCMODE_PWM1