Datasheet

Functional overview STM32L433xx
20/224 DocID028794 Rev 4
3.7 Boot modes
At startup, BOOT0 pin or nSWBOOT0 option bit, and BOOT1 option bit are used to select
one of three boot options:
• Boot from user Flash
• Boot from system memory
• Boot from embedded SRAM
BOOT0 value may come from the PH3-BOOT0 pin or from an option bit depending on the
value of a user option bit to free the GPIO pad if needed.
A Flash empty check mechanism is implemented to force the boot from system flash if the
first flash memory location is not programmed and if the boot selection is configured to boot
from main flash.
The boot loader is located in system memory. It is used to reprogram the Flash memory by
using USART, I2C, SPI, CAN or USB FS in Device mode through DFU (device firmware
upgrade).
3.8 Cyclic redundancy check calculation unit (CRC)
The CRC (cyclic redundancy check) calculation unit is used to get a CRC code using a
configurable generator polynomial value and size.
Among other applications, CRC-based techniques are used to verify data transmission or
storage integrity. In the scope of the EN/IEC 60335-1 standard, they offer a means of
verifying the Flash memory integrity. The CRC calculation unit helps compute a signature of
the software during runtime, to be compared with a reference signature generated at link-
time and stored at a given memory location.
3.9 Power supply management
3.9.1 Power supply schemes
• V
DD
= 1.71 to 3.6 V: external power supply for I/Os (V
DDIO1
), the internal regulator and
the system analog such as reset, power management and internal clocks. It is provided
externally through VDD pins.
• V
DD12
= 1.05 to 1.32 V: external power supply bypassing internal regulator when
connected to an external SMPS. It is provided externally through VDD12 pins and only
available on packages with the external SMPS supply option. VDD12 does not require
any external decoupling capacitance and cannot support any external load.
• V
DDA
= 1.62 V (ADCs/COMPs) / 1.8 (DACs/OPAMP) to 3.6 V: external analog power
supply for ADCs, DACs, OPAMPs, Comparators and Voltage reference buffer. The
V
DDA
voltage level is independent from the V
DD
voltage.
• V
DDUSB
= 3.0 to 3.6 V: external independent power supply for USB transceivers. The
V
DDUSB
voltage level is independent from the V
DD
voltage.
• V
LCD
= 2.5 to 3.6 V: the LCD controller can be powered either externally through VLCD
pin, or internally from an internal voltage generated by the embedded step-up
converter.
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