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Why Your STM32F103CBT7 TR is Not Entering Low Power Mode

Why Your STM32F103 CBT7TR is Not Entering Low Power Mode: Troubleshooting and Solutions

The STM32F103CBT7TR microcontroller, part of the STM32 family, is designed with power-saving modes to help extend battery life and reduce power consumption. If you are facing an issue where your STM32F103CBT7 TR is not entering low power mode as expected, there are a few key aspects that could be causing this issue. Let's break it down step by step and explore how to resolve it.

1. Check the Low Power Mode Configuration

Potential Cause: Incorrect configuration of the low power mode or improper initialization could prevent the microcontroller from entering low power mode.

Solution:

Review the Code: Ensure that the code properly configures the low-power mode (e.g., Sleep, Stop, or Standby mode). STM32 microcontrollers offer several low-power modes, and you must make sure that you are selecting the appropriate one based on your application requirements. Example: // Example code to enter Stop mode HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI); Use HAL or Direct Register Access : Depending on your method, ensure that you are using the correct API functions (HAL, SPL, or direct register manipulation) to trigger low-power modes.

2. Peripherals Preventing Low Power Mode

Potential Cause: Some peripherals may not be properly disabled or configured to allow low power modes. If peripherals such as USART, ADC, or GPIO pins are active, they may prevent the microcontroller from entering low-power mode.

Solution:

Disable Unused Peripherals: Ensure that all unused peripherals are disabled. This includes disabling Clock s to peripherals that are not needed in low power mode. For example: c __HAL_RCC_USART1_CLK_DISABLE(); // Disable USART1 clock HAL_UART_DeInit(&huart1); // Deinitialize USART1 Check for Active Interrupts: Interrupts from active peripherals can also prevent the MCU from entering low power mode. Make sure that interrupts are properly handled or disabled when entering low power mode.

3. GPIO Pins Holding the MCU Awake

Potential Cause: Certain GPIO pins may have been configured in a way that keeps the MCU awake. For example, pins that are configured as inputs with no pull-up or pull-down resistors may float and cause unwanted behavior.

Solution:

Configure GPIO Pins: Ensure that all unused GPIO pins are either configured as analog inputs (which consume less power) or set to a defined logic state (high or low). It is especially important to avoid floating inputs, which can cause the MCU to stay awake.

4. External Clock Source or PLL Configuration

Potential Cause: The system clock, or PLL configuration, might prevent the microcontroller from entering low power mode. Some low power modes require the use of the internal oscillator or disabling certain clock sources.

Solution:

Switch to Low-Speed Internal (LSI) Oscillator: When entering low-power modes like Stop or Standby, it's recommended to switch the system clock to a lower-power oscillator. Example: c HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_1); HAL_RCC_OscConfig(&RCC_OscInitStruct); // Set internal oscillator for low power mode

5. Interrupt and Sleep Mode Handling

Potential Cause: The microcontroller might be stuck in a loop waiting for an interrupt or external event, and hence, it's not entering the low-power state.

Solution:

Use WFI (Wait For Interrupt) or WFE (Wait For Event): Ensure that the system is correctly set to enter sleep mode by calling __WFI() or __WFE() to allow the MCU to enter low power mode when there are no pending interrupts. Example: __WFI(); // Enter Sleep mode, MCU will enter low power mode until an interrupt occurs

6. Watchdog Timer Preventing Low Power Mode

Potential Cause: If the watchdog timer (WDT) is running and not properly reset or disabled, it may prevent the MCU from entering low power mode.

Solution:

Disable the Watchdog: Ensure that the independent watchdog (IWDG) or the window watchdog (WWDG) is either disabled or properly configured. Example to disable IWDG: c IWDG->KR = 0xAAAA; // Disable the Independent Watchdog (IWDG)

7. Check for External Factors

Potential Cause: External factors like power supply issues or external interrupts could also interfere with the MCU's ability to enter low power mode.

Solution:

Ensure Stable Power Supply: Make sure that the power supply is stable, as fluctuations or noisy signals might affect the low power mode behavior. Review External Interrupt Sources: Double-check that no external interrupts are being triggered unnecessarily, preventing the MCU from entering low power mode.

Step-by-Step Troubleshooting Checklist:

Verify Code Configuration: Ensure correct configuration of low power modes in your code. Disable Unnecessary Peripherals: Turn off unused peripherals and disable unused GPIOs. Set Low-Speed Internal Oscillator: Switch to a lower power oscillator if applicable. Check Interrupts and Events: Ensure that interrupts are not holding the MCU from entering low power mode. Check the Watchdog Timer: Disable or properly configure any watchdog timers. Review External Factors: Make sure external factors like power supply and external interrupt sources are not interfering.

By systematically addressing each of these factors, you can resolve the issue of the STM32F103CBT7TR not entering low power mode and ensure it functions as intended with minimal power consumption.

Let me know if you need further assistance with any specific steps or more details on the solution!