Datasheet

DS10969 Rev 5 19/204
STM32L475xx Functional overview
57
3.7 Boot modes
At startup, BOOT0 pin 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
The boot loader is located in system memory. It is used to reprogram the Flash memory by
using USART, I2C, SPI, CAN or USB OTG 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 (DAC/OPAMPs) to 3.6 V: external analog power
supply for ADCs, DAC, 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
BAT
= 1.55 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and
backup registers (through power switch) when V
DD
is not present.
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 20: 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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