Dear Team,
How to configure the BOOT0 pin of this module.
In the reference design it is let floating with an option to pull up.
In the application note (How to develop RF hardware using STM32WBA MCUs - Application note) it is pulled down.
May I know in all these three configurations(Pull up, Pull down, floating) what will be happening. From where it is booting.
You have any document which describes how to configure this BOOT0 pin.
Regards
Hariom
Function of the BOOT0 Pin
The BOOT0 pin determines where the microcontroller will start execution after a reset (boot mode). Depending on its logic level at reset, the STM32 can boot from:
Main Flash (user application memory)
System memory (factory bootloader: UART, USB, etc.)
SRAM (in some STM32 families)
:gear: BOOT0 Behavior in STM32WBA5MMG
According to the Reference Manual RM0492 and application notes for the STM32WBA series:
BOOT0 Level Boot Source
| 0 (GND) | Boot from Main Flash (user code) |
| 1 (VDD) | Boot from System Memory (internal bootloader) |
:white_heavy_check_mark: BOOT0 = 0 → Executes user application from Flash
:repeat_button: BOOT0 = 1 → Enters bootloader (e.g., for DFU via USB or UART)
:electric_plug: Possible BOOT0 Pin Configurations
Physical Setup Expected Behavior
| Pull-down (to GND) | MCU always boots from Flash (normal mode) |
| Pull-up (to VDD) | MCU enters bootloader mode |
| Floating (not connected) | Undetermined behavior / may pick up noise |
:prohibited: Avoid leaving BOOT0 floating — it can result in unpredictable boot behavior!
:open_book: Practical Recommendations
For final products: use a 10kΩ pull-down resistor to ensure boot from Flash.
For firmware updates via bootloader (e.g., USB DFU):
You can add a jumper or button to pull BOOT0 high before a reset.In the schematic shown: there’s a jumper (possibly labeled DNF – Do Not Fit) allowing pull-up to VDD, which can be used for bootloader mode.
:books: Useful Documents
RM0492 – STM32WBA Reference Manual, see the Boot configuration section
AN2606 – STM32 Microcontroller System Memory Boot Mode (detailed bootloader guide)
AN5522 – How to develop RF hardware using STM32WBA MCUs (mentioned in the question)
