PCB LITE blog

Why STM32L476RCT6 PWM Output is Not Working

Analysis of the Issue: "Why STM32L476RCT6 PWM Output is Not Working"

When the PWM (Pulse Width Modulation) output on the STM32L476RCT6 is not working as expected, the problem could arise from several factors. Below, we will go step by step to analyze the potential causes, the possible sources of the issue, and how to resolve it.

1. Check the Initialization of PWM Settings

The first thing to verify is whether the PWM settings on the STM32L476RCT6 have been initialized properly in the code.

Potential Issue:

Incorrect timer or PWM configuration. Missing initialization of the PWM parameters (such as frequency, duty cycle, and timer settings).

Solution:

Ensure that the timer is properly initialized. Use STM32CubeMX to configure the timers and peripherals. Verify that the correct timer is chosen for PWM output, and make sure it is enabled. In the code, double-check the configuration of the prescaler, auto-reload value, and compare match values for the timer to ensure they match your desired PWM frequency and duty cycle. 2. Verify GPIO Pin Configuration

PWM output is generated on specific GPIO pins. If the GPIO pin is not properly configured, the PWM signal will not be generated.

Potential Issue:

Incorrect GPIO pin configuration (e.g., wrong pin mode or alternate function setting). The pin is set to a default state instead of being configured for the PWM output.

Solution:

Make sure the GPIO pin that is supposed to output PWM is configured for the correct alternate function. This can be done through STM32CubeMX or directly in the code. Set the GPIO pin to the alternate function mode corresponding to the PWM output (e.g., AF1, AF2, etc., depending on the timer). 3. Check Timer Clock Source

If the timer clock is not properly configured, the PWM signal might not be generated.

Potential Issue:

Incorrect clock source for the timer. The timer might not be getting the clock signal it needs to operate.

Solution:

Ensure that the timer's clock is enabled in the RCC (Reset and Clock Control) settings. Check if the correct clock source is selected (e.g., using the APB1 or APB2 clock for timers). If using a high-frequency clock (like an external oscillator), ensure it is properly configured and enabled. 4. Verify Timer's Output Enable

Even if the timer is properly set up, the PWM output may not work if the timer's output is disabled.

Potential Issue:

The PWM output might be disabled in the timer configuration.

Solution:

Make sure that the PWM output is explicitly enabled in the timer settings. For STM32L476RCT6, this is done by configuring the timer’s output compare mode to PWM mode. Ensure that the correct channel of the timer is enabled for PWM output. 5. Check for Conflicting Peripheral Configurations

If multiple peripherals share the same timer or GPIO pin, conflicts could occur.

Potential Issue:

Conflicting peripheral configurations can cause the timer to be overridden or not function properly.

Solution:

Use STM32CubeMX to check if the timer is being used by another peripheral. If it is, make sure to reassign the peripherals to different timers or GPIO pins. 6. Verify the Timer's Counter Configuration

If the timer’s counter is misconfigured, PWM output may not behave correctly.

Potential Issue:

The timer counter might not be started, or it might not be set to continuous mode.

Solution:

Check if the timer counter is enabled and properly started. Ensure that the timer is in continuous mode and not in one-shot mode unless intended. 7. Debugging and Troubleshooting

If the PWM still isn't working after checking all configurations, further debugging is necessary.

Potential Issue:

Code errors, missing function calls, or hardware issues could still be the source of the problem.

Solution:

Use a debugger (e.g., ST-Link) to step through the code and check if the timer’s registers and GPIO configurations are correctly set at runtime. Check the physical circuit with an oscilloscope or logic analyzer to ensure that the PWM signal is not being affected by external factors.

Step-by-Step Solution Summary

Initialize Timer and PWM Settings: Use STM32CubeMX to configure the timer. Ensure the timer parameters (prescaler, period, duty cycle) are set correctly. Configure GPIO Pin: Set the GPIO pin to the correct alternate function mode. Ensure the pin is assigned to the correct timer output. Check Timer Clock Source: Enable the appropriate clock for the timer in the RCC settings. Enable PWM Output: Ensure that the timer’s PWM output is explicitly enabled and properly configured. Check for Peripheral Conflicts: Verify that no other peripheral is using the same timer or GPIO pin. Verify Timer Counter Configuration: Ensure the timer counter is enabled and in the correct mode. Debug and Troubleshoot: Use debugging tools and external measurement equipment to verify the configuration and troubleshoot further.

By following these steps, you should be able to identify and fix the problem causing the PWM output to fail on the STM32L476RCT6.