How to Generate PWM with DMA in STM32

Pulse Width Modulation (PWM) is one of the most common techniques in embedded systems. In simple words, PWM controls the amount of power delivered to devices by switching a signal on and off very fast. Because of this, you can dim an LED, control the speed of a motor, or even generate audio signals with just a microcontroller pin.

In STM32 microcontrollers, PWM generation becomes very simple because the timers have built-in support. You only need to configure the timer, select the channel, and set the frequency and duty cycle. After that, the hardware takes care of generating a clean PWM signal.

Compared to manually toggling GPIOs, using timers is much more accurate and efficient. As a result, PWM in STM32 is widely used in robotics, automation, motor drivers, LED brightness control, and many other real-world projects.

In this tutorial, you will learn step by step how to configure PWM on STM32 using STM32CubeMX and the HAL library. First, we will look at the basic concept of PWM and timers. Then, we will configure the project in CubeMX, generate code, and finally test the output on real hardware.

What is PWM (Pulse Width Modulation)?

Pulse Width Modulation (PWM) is a technique to control the average voltage or power delivered to a device by switching a signal between ON and OFF very quickly. The main idea is simple: the longer the signal stays ON compared to OFF, the more power the device receives. This ratio is called the duty cycle, while the speed of switching is called the frequency.

For example, a 50% duty cycle means the signal stays ON for half the time and OFF for the other half. As a result, the device receives about half of the maximum possible power. By adjusting the duty cycle, you can dim LEDs, control motor speed, or manage the intensity of heaters.

PWM is efficient because the switching happens fast, and the power loss is very low compared to analog methods like resistors or voltage regulators.

PWM in Microcontrollers (MCU)

Microcontrollers (MCUs) like the STM32 have built-in timers that make PWM generation very easy. Instead of manually toggling pins, the hardware timers automatically create precise PWM signals at the frequency and duty cycle you choose.

With STM32, you can configure PWM using STM32CubeMX and then control it in code with the HAL library. This approach ensures accuracy and frees up the CPU for other tasks.

In real-world projects, PWM in microcontrollers is everywhere — from controlling DC motors in robots to adjusting LED brightness in displays. Because it is both powerful and simple, PWM is often the first concept you learn when starting with STM32.

STM32 Timer Overview for PWM

Timer modes relevant to PWM

STM32 microcontrollers include powerful timers that can directly generate PWM signals. These timers run independently from the CPU, which means you can produce accurate waveforms without using much processing power.

For PWM, the most commonly used timer modes are:

• Up-counting mode: The timer starts counting from 0 and goes up to the value in the Auto-Reload Register (ARR). After reaching this value, the timer resets and starts again.
• PWM Mode 1: The output stays HIGH while the counter is less than the compare value (CCR). It switches LOW when the counter goes above the CCR value.
• PWM Mode 2: The opposite of Mode 1. The output stays LOW when the counter is less than CCR and becomes HIGH afterward.

By selecting the right mode, you can decide how your PWM waveform behaves.

The image above shows how the timer counter compares with ARR and CCR to generate a PWM output.

• The blue line is the counter increasing up to ARR.
• The red line (CCR) decides when the output switches from HIGH to LOW.
• The green waveform is the actual PWM signal produced.

Frequency and duty cycle basics

Every PWM signal has two important properties: frequency and duty cycle.

• PWM frequency tells how many times the signal completes a full cycle in one second. It depends on three parameters: timer clock, prescaler (PSC), and ARR.
  Formula:PWM frequency = Timer clock / (PSC + 1) / (ARR + 1)
• Duty cycle defines the percentage of ON-time in each cycle. It depends on the compare register (CCR) value.
  Formula:Duty cycle (%) = (CCR / (ARR + 1)) × 100

For example, if ARR = 999 and CCR = 500, then the duty cycle = 50%. This means the signal stays HIGH for half the time and LOW for the other half.

The image above shows PWM signals with 25%, 50%, and 75% duty cycles.

Hardware Required for STM32 PWM Tutorial

To follow this tutorial, you will need the following hardware:

• STM32F446 Dev Board (e.g., STM32F4, STM32F7, STM32H7, or any board with ADC support)
• Breadboard (for easy circuit connections)
• Jumper Wires (male-to-male for connections)
• USB Cable (to connect the STM32 board to the PC for programming and debugging)

Configuring PWM using STM32CubeMX

I am using the STM32F103C8 (BluePill) for this project. We will start with the Clock Configuration.

STM32 Clock Configuration

The clock configuration for the project is shown in the image below.

• External Crystal (8MHz) is used to provide the clock via the PLL and the system is running at maximum 72MHz clock.
• I am going to use the TIM1 for the PWM, which is connected to the APB2 Bus.
• The APB2 Timer clock is at 72MHz right now and that makes TIM1 clock = 72MHz.

STM32 PWM Timer Configuration

I am going to use the Timer 1 to generate the PWM signal. The Timer1 PWM configuration is shown in the image below.

The detailed description of the image is mentioned below.

Timer Setting

• Clock Source: Internal Clock
  This sets the timer to use the internal APB2 clock as its source. It’s essential for generating precise time-based signals like PWM without relying on external clocks.
• Channel1: PWM Generation CH1
  This enables PWM output on Channel 1 of TIM1. It’s what makes the timer output a PWM signal rather than just counting.

Counter Settings

• Prescaler (PSC = 72-1)
  This divides the timer’s input clock frequency by 72.
  For example, if the APB clock is 72 MHz, the timer counts at 1 MHz after prescaling.
• Counter Mode: Up
  The timer counts from 0 up to the value in the AutoReload Register (ARR), then resets and starts over. This is the typical mode for PWM.
• Counter Period (ARR = 100-1)
  Sets the maximum count value (100 – 1 = 99), which defines the PWM frequency in combination with the prescaler.
  PWM Frequency = Timer Clock / (PSC + 1) / (ARR + 1)
  → For 72 MHz APB clock:
  → PWM Frequency = 72 MHz / 72 / 100 = 10 kHz

PWM Generation Channel 1 Settings

• Mode: PWM mode 1
  This sets the PWM output to PWM Mode 1, which means:
  • Output is HIGH when the counter is less than the pulse value.
  • Output is LOW when the counter is greater than or equal to the pulse value.
• Pulse (CCR1) = 0
  This defines the initial duty cycle — in this case, it’s 0, meaning no ON time.
  The output will stay LOW until this value is changed in code.

Pin Mapping (PA8 – TIM1_CH1)

• PA8 (TIM1_CH1)
  This is the GPIO pin where the PWM signal will appear.
  It is automatically configured as an alternate function output for TIM1 Channel 1. You can connect an LED, motor driver, or other device to this pin to control it with PWM.

PWM DMA Configuration

The image below shows the CubeMX Configuration for the STM32 PWM DMA Mode.

You can choose any DMA stream that is available for the specific Timer channel you are using. The important point here is to configure the DMA direction as Memory to Peripheral, because the PWM duty cycle (pulse width values) will be fetched from memory and written into the Timer’s Capture/Compare register (CCR).

For the data width, I selected Half Word (16-bit, uint16_t). This is because the Timer registers (such as CCR1, CCR2, etc.) are 16-bit wide on most STM32 devices. If your pulse width values fit within 16 bits, using Half Word is the most efficient choice.

PWM DMA Modes

Now, let’s talk about Normal and Circular mode:

• Normal Mode:
  In this mode, DMA transfers the data from memory to the Timer only once. For example, if you have an array of pulse widths stored in memory, DMA will move them one by one to the Timer CCR, and after the last value is sent, the transfer stops.
  • Best suited for one-time waveform generation, like sending a predefined burst of pulses.
  • After completion, if you want to generate more waveforms, you need to restart the DMA manually.
• Circular Mode:
  In this mode, once DMA finishes transferring all values from the memory buffer, it automatically loops back and starts again from the beginning. This process continues endlessly until you stop it.
  • Ideal for continuous waveform generation, such as creating repetitive PWM patterns (sine wave, triangular wave, etc.).
  • Since the CPU doesn’t need to restart the transfer, it reduces processor overhead and ensures smooth, uninterrupted PWM output.

We will see both the modes, but I will start with Normal Mode first.

Why do we need to use -1 ?

In STM32 timers, the Prescaler (PSC) and Auto-Reload Register (ARR) work in a way that they automatically add +1 to the value you enter. This means if you write a value of PSC = 71, the timer actually divides the clock by 72. Similarly, if you set ARR = 999, the counter counts up to 1000.

That’s why, when calculating values for frequency or period, we subtract 1 in the formula to match the hardware behavior.

Writing Code for PWM with HAL (Without DMA)

The STM32 HAL library makes it easier to configure and control PWM signals without dealing directly with low-level registers. Let’s break down the process step by step.

Initializing the Timer

First, initialize the timer for PWM mode. When you generate code from STM32CubeMX, it automatically creates initialization functions such as MX_TIMx_Init(). This function sets the prescaler (PSC), auto-reload register (ARR), and configures the timer in PWM mode.

In addition, CubeMX configures the GPIO pin linked to your timer channel in Alternate Function mode, so that the PWM signal can appear on the physical pin.

Starting PWM Output

After initialization, start the PWM output using the HAL function:

HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

Here:

• htim1 is the timer handle generated by CubeMX.
• TIM_CHANNEL_1 selects the PWM channel (Channel 1 in this case).

You can repeat the same function with TIM_CHANNEL_2, TIM_CHANNEL_3, or TIM_CHANNEL_4 if your timer supports multiple channels.

Changing Duty Cycle in Code

To change the duty cycle at runtime, update the Capture/Compare Register (CCR). For example:

TIM1->CCR1 = 30;  // Set duty cycle value <= ARR

TIM1->CCR1 = 30;  // Set duty cycle value <= ARR

• The value written to CCR1 controls the ON-time of the signal.
• A higher CCR value means a longer pulse (higher duty cycle).
• A smaller CCR value means a shorter pulse (lower duty cycle).

The duty cycle is calculated using the formula:

This method allows you to dynamically adjust brightness of an LED, speed of a motor, or any other load connected to the PWM pin.

Complete PWM Code

You can refer to the main function below to change the duty cycle at the Runtime.

int main(void)
{
  HAL_Init();
  SystemClock_Config();  // System clock setup
  MX_GPIO_Init();        // GPIO init
  MX_TIM1_Init();        // Timer1 init with PWM

  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);
  while (1)
  {
    /* Example: Update duty cycle dynamically */
    for (int duty = 0; duty <= 99; duty += 10)
    {
      __HAL_TIM_SET_COMPARE(&htim1, TIM_CHANNEL_1, duty);  // TIM1->CCR1 = duty;
      HAL_Delay(500);  // Wait 500ms before changing duty cycle
    }
  }
}

int main(void)
{
  HAL_Init();
  SystemClock_Config();  // System clock setup
  MX_GPIO_Init();        // GPIO init
  MX_TIM1_Init();        // Timer1 init with PWM

  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);
  while (1)
  {
    /* Example: Update duty cycle dynamically */
    for (int duty = 0; duty <= 99; duty += 10)
    {
      __HAL_TIM_SET_COMPARE(&htim1, TIM_CHANNEL_1, duty);  // TIM1->CCR1 = duty;
      HAL_Delay(500);  // Wait 500ms before changing duty cycle
    }
  }
}

The code above gradually changes the PWM duty cycle from 0% to 100%. It increases the duty cycle in 10% steps, and each step occurs every 500 milliseconds.

STM32 PWM Generation Result

The image below show the PWM pulse captured on the Logic Analyser.

PWM waveform above has the following characteristics:

• Frequency: 10 kHz — each complete cycle lasts 100 microseconds.
• Duty Cycle: 30% — the signal stays HIGH for 30 microseconds and LOW for 70 microseconds in each cycle.
• The waveform clearly displays consistent pulse spacing and width, confirming stable PWM output.

The gif below shows the duty cycle changing every 500ms (press the Play Button). It varies from 0 to 100% in step of 10%.

STM32 PWM DMA Normal Mode Example

In this example, we will learn how to generate PWM signals on an STM32 microcontroller using DMA in Normal Mode. The idea is to preload an array of pulse width values in memory and let DMA transfer these values to the Timer’s Capture/Compare register (CCR). As the transfer happens, the PWM duty cycle changes automatically without CPU intervention.

Since we are using Normal Mode, the DMA will execute the transfer only once. Once the last value from the array is written, the transfer stops, and the PWM output will remain steady at the final duty cycle value.

This approach greatly reduces CPU workload because the duty cycle updates are handled by DMA, while the processor can continue with other tasks.

The main function below demonstrates how to send an array of pulse widths to the DMA.

uint16_t pwmData[11];
int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_TIM1_Init();
//  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

  pwmData[0] = 10; pwmData[1] = 20; pwmData[2] = 30;
  pwmData[3] = 40; pwmData[4] = 50; pwmData[5] = 60;
  pwmData[6] = 70; pwmData[7] = 80; pwmData[8] = 90;
  pwmData[9] = 100;pwmData[10] = 0;
  HAL_TIM_PWM_Start_DMA(&htim1, TIM_CHANNEL_1, (uint32_t *)pwmData, 11);
  while(1){
  }
}

uint16_t pwmData[11];
int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_TIM1_Init();
//  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

  pwmData[0] = 10; pwmData[1] = 20; pwmData[2] = 30;
  pwmData[3] = 40; pwmData[4] = 50; pwmData[5] = 60;
  pwmData[6] = 70; pwmData[7] = 80; pwmData[8] = 90;
  pwmData[9] = 100;pwmData[10] = 0;
  HAL_TIM_PWM_Start_DMA(&htim1, TIM_CHANNEL_1, (uint32_t *)pwmData, 11);
  while(1){
  }
}

First, we load the desired duty cycle values into the pwmData array. Since the Timer’s ARR (Auto Reload Register) is set to 100, each value directly represents the duty cycle in percentage. For example, a value of 10 corresponds to 10% duty, 20 to 20% duty, and so on. At the end of the array, we place a 0, which forces the PWM output pin to go LOW once the sequence finishes.

After preparing the array, we call HAL_TIM_PWM_Start_DMA, which transfers all the values to the Timer using DMA. Because the DMA is configured in Normal Mode, it sends the 11 values only once. When the transfer completes, the PWM output stays fixed at the final duty cycle value (0).

Result of PWM DMA Normal Mode

The image below shows the Complete PWM wave on the Logic Analyzer.

You can see that we only get a single PWM Wave with varying Duty cycles. The PWM frequency is fixed at 10KHz, same as what we configured in the CubeMX.

The image below shows the Duty cycles of the PWM waveform.

We get the Duty cycle ranging from 10%(1-us) to 100% (visually we can’t show it).

STM32 PWM DMA Circular Mode Example

In this example, we will learn how to generate PWM signals on an STM32 microcontroller using DMA in Circular Mode. Similar to Normal Mode, we preload an array of pulse width values in memory and let DMA transfer these values to the Timer’s Capture/Compare register (CCR). As the transfer happens, the PWM duty cycle changes automatically without CPU involvement.

The difference here is that in Circular Mode, once DMA finishes sending all the values in the array, it automatically starts again from the beginning. This creates a continuous loop of duty cycle updates, making it ideal for generating repetitive waveforms such as sine waves, triangular waves, or any custom pattern.

This method allows the PWM output to run indefinitely with changing duty cycles, while keeping the CPU free for other tasks. The processor does not need to restart the DMA transfer, which ensures smooth and uninterrupted waveform generation.

In order to use the DMA in circular mode, we must configure it in CubeMX as shown in the DMA Configuration Image.

The main function below demonstrates how to send an array of pulse widths to the DMA in Circular Mode.

uint16_t pwmData[13];
int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_TIM1_Init();
//  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

  pwmData[0] = 10; pwmData[1] = 20; pwmData[2] = 30;
  pwmData[3] = 40; pwmData[4] = 50; pwmData[5] = 60;
  pwmData[6] = 70; pwmData[7] = 80; pwmData[8] = 90;
  pwmData[9] = 100;pwmData[10] = 0; pwmData[11] = 0;
  pwmData[12] = 0;
  HAL_TIM_PWM_Start_DMA(&htim1, TIM_CHANNEL_1, (uint32_t *)pwmData, 13);
  while(1){
  }
}

uint16_t pwmData[13];
int main(void)
{
  HAL_Init();
  SystemClock_Config();
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_TIM1_Init();
//  HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_1);

  pwmData[0] = 10; pwmData[1] = 20; pwmData[2] = 30;
  pwmData[3] = 40; pwmData[4] = 50; pwmData[5] = 60;
  pwmData[6] = 70; pwmData[7] = 80; pwmData[8] = 90;
  pwmData[9] = 100;pwmData[10] = 0; pwmData[11] = 0;
  pwmData[12] = 0;
  HAL_TIM_PWM_Start_DMA(&htim1, TIM_CHANNEL_1, (uint32_t *)pwmData, 13);
  while(1){
  }
}

First, we load the desired duty cycle values into the pwmData array. For example, a value of 10 corresponds to 10% duty, 20 to 20% duty, and so on. At the end of the array, we place three 0, which forces the PWM output pin to stay LOW once the sequence finishes. This will help us distinguish between successive waveforms.

Once the array is ready, we call HAL_TIM_PWM_Start_DMA, which begins transferring the values to the Timer via DMA. Because the DMA is set to Circular Mode, all 13 values are sent in a loop continuously, without requiring any intervention from the CPU.

Result of PWM DMA Normal Mode

The image below shows the Complete PWM waves on the Logic Analyzer.

As shown in the image, Circular DMA generates a continuous series of PWM waveforms. The duty cycle in each waveform gradually increases from 10% to 100%, and at the end, the output stays LOW for a short duration due to the three 0 values we added at the end of the array.

How to Stop PWM Circular DMA

When the DMA finishes transferring all values from the array, it triggers an interrupt, which calls the PWM_PulseFinishedCallback function. Inside this callback, you can write custom code—for example, to stop the DMA from sending any further values or to perform other actions once the PWM sequence completes.

int count = 0;

void HAL_TIM_PWM_PulseFinishedCallback(TIM_HandleTypeDef *htim){
	count++;
	if (count == 3){
		HAL_TIM_PWM_Stop_DMA(htim, TIM_CHANNEL_1);
	}
}

int count = 0;

void HAL_TIM_PWM_PulseFinishedCallback(TIM_HandleTypeDef *htim){
	count++;
	if (count == 3){
		HAL_TIM_PWM_Stop_DMA(htim, TIM_CHANNEL_1);
	}
}

A counter count tracks how many times the PWM sequence completes. Each time the HAL_TIM_PWM_PulseFinishedCallback is called, the counter increments. When it reaches 3, HAL_TIM_PWM_Stop_DMA stops the DMA on Timer Channel 1, allowing the PWM to run three full cycles before stopping automatically.

The image below shows the circular PWM being stopped after 3 cycles.

To explore a more practical and application-specific example of Circular DMA mode, check out STM32 PWM using DMA. This tutorial provides detailed steps, code examples, and waveform explanations that show how DMA can be used to generate efficient and continuous PWM signals on STM32 microcontrollers.

Applications of PWM in STM32

LED Dimming

PWM allows precise control over LED brightness by adjusting the duty cycle. This technique is widely used in lighting systems and displays to achieve energy-efficient illumination.

Motor Control

By varying the duty cycle, PWM enables control over motor speed and torque. This is essential in applications like robotics, fans, and servo motors, where precise motion control is required.

Communication Protocols

PWM can be utilized in communication systems to encode data. By modulating the pulse width, information can be transmitted between devices, making it useful in various signaling applications.

Troubleshooting PWM Issues

Incorrect Frequency Output

Ensure that the timer’s prescaler and auto-reload register (ARR) are correctly configured to achieve the desired frequency. Double-check the system clock settings in STM32CubeMX to confirm that the timer is receiving the correct clock source.

Duty Cycle Not Updating

If changes to the duty cycle aren’t reflected in the output, verify that the compare register (CCR) is being updated correctly. Additionally, ensure that the timer is running and not in a stopped state.

Pin or Channel Mismatch

Confirm that the PWM output pin is correctly mapped to the timer channel in STM32CubeMX. Mismatches between the configured pin and the actual hardware connection can lead to no output signal.

Conclusion

This tutorial successfully demonstrates how to generate a PWM signal using an STM32 microcontroller. We learned how to configure timers in STM32CubeMX, start PWM output using HAL functions, and adjust the duty cycle to observe changes in the waveform. You can apply this knowledge to practical applications such as dimming LEDs, controlling motor speed, or generating analog-style signals.

In the next tutorials, we will explore advanced topics like PWM input measurement, using DMA with PWM, and generating three-phase PWM signals for motor control. These lessons will help you take your STM32 projects to the next level.

STM32 TIMERS #2. How to Measure PWM Input

STM32 TIMERS #3. How to use the ENCODER Mode

STM32 Input Capture Example – HAL_TIM_IC_CaptureCallback for Frequency, Pulse Width

STM32 TIMERS #5. Timer synchronization || Slave Trigger mode

STM32 TIMERS #6. Timer synchronization || Generate 3 Phase PWM

STM32 TIMERS #7. Timer synchronization || Slave Reset mode

STM32 TIMERS #8. Make 48 bit Counter by Cascading Timers

STM32 Timers #9. One Pulse Mode

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