Why STM32F100RBT6B May Be Stuck in Bootloader Mode

Why STM32F100RBT6B May Be Stuck in Bootloader Mode

Why STM32F100RBT6B May Be Stuck in Bootloader Mode and How to Resolve It

Introduction

The STM32F100RBT6B microcontroller may sometimes get stuck in bootloader mode. This can be frustrating, especially if you are working on firmware development or debugging your system. In this article, we'll explore the possible causes of the issue and provide a step-by-step solution to resolve it.

Possible Causes

Boot Mode Pin Configuration Issue The STM32F100RBT6B has a dedicated pin (BOOT0) that determines the boot mode at startup. If this pin is inadvertently set to high (logic 1) during Power -up or reset, the microcontroller will enter the bootloader mode instead of running user application code. Incorrect Firmware Flashing If the STM32F100RBT6B was flashed with incorrect or incomplete firmware, the microcontroller may be unable to exit bootloader mode, as it cannot properly load or run the application code. Low Power or Power Supply Issues An unstable or insufficient power supply can cause the microcontroller to behave unpredictably. If the system does not provide the correct voltage during startup, it may fail to boot the user application and stay in bootloader mode. JTAG or SWD interface Interference If the JTAG or SWD interface is actively connected or improperly configured, it can prevent the STM32 from booting normally. The presence of debugger interfaces can force the microcontroller into a debug mode, making it seem as though it is stuck in bootloader mode. Watchdog Timer or Reset Issues A watchdog timer that is not properly managed can cause repeated resets, forcing the system to continuously enter bootloader mode. Similarly, improper handling of external reset signals can lead to the device remaining in a reset state or bootloader mode.

Step-by-Step Solution

Step 1: Check BOOT0 Pin Configuration

Action: First, verify the state of the BOOT0 pin. By default, this pin should be held low (0) to allow the STM32 to boot from flash memory.

Solution: Ensure that the BOOT0 pin is connected to ground (0V). If it’s floating or connected to a high voltage (3.3V), it will trigger bootloader mode.

How to Fix: If the pin is incorrectly set, use a jumper or resistor to pull the BOOT0 pin to ground. After this, reset the microcontroller and check if it exits bootloader mode.

Step 2: Reflash the Firmware

Action: If the microcontroller is stuck in bootloader mode, it’s possible that the firmware is corrupt or missing.

Solution: Reflash the STM32F100RBT6B with the correct, verified firmware. Use a tool like STM32CubeProgrammer or a compatible flashing tool to upload the correct firmware to the microcontroller.

How to Fix:

Connect the STM32 to your PC via a USB to serial adapter or a dedicated ST-Link programmer. Open STM32CubeProgrammer and select the connected device. Reflash the correct binary file to the STM32F100RBT6B. After flashing, reset the microcontroller and check if it runs the correct application code. Step 3: Power Supply Check

Action: Ensure that the microcontroller is receiving a stable and sufficient power supply.

Solution: Measure the supply voltage to the STM32F100RBT6B and ensure that it is within the specified range (typically 3.3V).

How to Fix: If the power supply is unstable, replace or fix the power supply circuit to ensure it provides a clean 3.3V or the appropriate voltage for your system. A faulty power supply can lead to the microcontroller entering bootloader mode or failing to boot correctly.

Step 4: Disable Debugger Interfaces

Action: If you are using a debugger like JTAG or SWD, ensure that the debugger is not interfering with the boot process.

Solution: Disconnect any debugger interfaces (e.g., ST-Link, JTAG) from the STM32F100RBT6B and attempt to reset the device.

How to Fix:

Physically disconnect the debugger. Ensure that no debugger interface is enabled in the configuration. Reset the microcontroller and check if it boots properly. Step 5: Watchdog Timer and Reset Handling

Action: Investigate the state of the watchdog timer and external reset signals.

Solution: If the watchdog timer is enabled and not properly cleared, it could cause the microcontroller to reset continuously. Similarly, if the reset circuit is malfunctioning, the microcontroller might never leave the reset state and stay in bootloader mode.

How to Fix:

Disable the watchdog timer in your firmware (or configure it correctly if you need it). Ensure that external reset circuits are properly connected and functioning. If necessary, initiate a manual reset to exit bootloader mode.

Conclusion

By following these steps, you should be able to identify and resolve the issue of the STM32F100RBT6B being stuck in bootloader mode. The most common causes are incorrect BOOT0 pin configuration, corrupted firmware, power supply issues, debugger interference, and improper reset handling. By checking and addressing these areas, you can get your STM32F100RBT6B back to running your desired application code.

If the issue persists after trying these solutions, there could be a hardware fault, and further diagnostics may be needed.