This is the vv1.21.0 version of the MicroPython documentation. The latest development version of this page may be more current.

stm — functionality specific to STM32 MCUs

This module provides functionality specific to STM32 microcontrollers, including direct access to peripheral registers.

Memory access

The module exposes three objects used for raw memory access.


Read/write 8 bits of memory.


Read/write 16 bits of memory.


Read/write 32 bits of memory.

Use subscript notation [...] to index these objects with the address of interest.

These memory objects can be used in combination with the peripheral register constants to read and write registers of the MCU hardware peripherals, as well as all other areas of address space.

Peripheral register constants

The module defines constants for registers which are generated from CMSIS header files, and the constants available depend on the microcontroller series that is being compiled for. Examples of some constants include:


Base address of the GPIOA peripheral.


Base address of the GPIOB peripheral.


Offset of the GPIO bit set/reset register.


Offset of the GPIO input data register.


Offset of the GPIO output data register.

Constants that are named after a peripheral, like GPIOA, are the absolute address of that peripheral. Constants that have a prefix which is the name of a peripheral, like GPIO_BSRR, are relative offsets of the register. Accessing peripheral registers requires adding the absolute base address of the peripheral and the relative register offset. For example GPIOA + GPIO_BSRR is the full, absolute address of the GPIOA->BSRR register.

Example use:

# set PA2 high
stm.mem32[stm.GPIOA + stm.GPIO_BSRR] = 1 << 2

# read PA3
value = (stm.mem32[stm.GPIOA + stm.GPIO_IDR] >> 3) & 1

Functions specific to STM32WBxx MCUs

These functions are available on STM32WBxx microcontrollers, and interact with the second CPU, the RF core.


Returns the status of the second CPU as an integer (the first word of device info table).


Get the version of the firmware running on the second CPU. Pass in 0 for id to get the FUS version, and 1 to get the WS version.

Returns a 5-tuple with the full version number.

stm.rfcore_sys_hci(ogf, ocf, data, timeout_ms=0)

Execute a HCI command on the SYS channel. The execution is synchronous.

Returns a bytes object with the result of the SYS command.

Functions specific to STM32WLxx MCUs

These functions are available on STM32WLxx microcontrollers, and interact with the integrated “SUBGHZ” radio modem peripheral.


Sets the internal SPI CS pin attached to the radio peripheral. The level argument is active-low: a truthy value means “CS pin high” and de-asserts the signal, a falsey value means “CS pin low” and asserts the signal.

The internal-only SPI bus corresponding to this CS signal can be instantiated using machine.SPI() id value "SUBGHZ".


Sets the internal SUBGHZ radio interrupt handler to the provided function. The handler function is called as a “hard” interrupt in response to radio peripheral interrupts. See Writing interrupt handlers for more information about interrupt handlers in MicroPython.

Calling this function with the handler argument set to None disables the IRQ.

Due to a hardware limitation, each time this IRQ fires MicroPython disables it before calling the handler. In order to receive another interrupt, Python code should call subghz_irq() to set the handler again. This has the side effect of re-enabling the IRQ.


Return a bool corresponding to the internal “RFBUSYS” signal from the radio peripheral. Before sending a new command to the radio over SPI then this function should be polled until it returns False, to confirm the busy signal is de-asserted.