Datasheet

DocID028798 Rev 3 17/155
STM32L432KB STM32L432KC Functional overview
49
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 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
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.
Note: When the functions supplied by V
DDA
or V
DDUSB
are not used, these supplies should
preferably be shorted to V
DD
.
Note: If these supplies are tied to ground, the I/Os supplied by these power supplies are not 5 V
tolerant (refer to
Table 18: Voltage characteristics).
Note: V
DDIOx
is the I/Os general purpose digital functions supply. V
DDIOx
represents V
DDIO1
, with
V
DDIO1
= V
DD
.
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