Cyclic Redundancy Check Calculation Unit (Crc); Power Management; Power Supply Schemes; Power Supply Supervisors - STMicroelectronics STM32F042G4 Manual

Functional overview
3.4

Cyclic redundancy check calculation unit (CRC)

The CRC (cyclic redundancy check) calculation unit is used to get a CRC code from a 32-bit
data word and a CRC-32 (Ethernet) polynomial.
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.
3.5

Power management

3.5.1

Power supply schemes


V
DD
externally through V

V
DDA
PLL (minimum voltage to be applied to V
voltage level must be always greater or equal to the V
provided first.

V
DDIO2
through the VDDIO2 pin. The V
or V
diagrams or tables for concerned I/Os list.

V
BAT
backup registers (through power switch) when V
3.5.2

Power supply supervisors

The device has integrated power-on reset (POR) and power-down reset (PDR) circuits.
They are always active, and ensure proper operation above a threshold of 2 V. The device
remains in reset mode when the monitored supply voltage is below a specified threshold,
V
POR/PDR

The POR monitors only the V
that V

The PDR monitors both the V
supply supervisor can be disabled (by programming a dedicated Option bit) to reduce
the power consumption if the application design ensures that V
equal to V
The V
DDIO2
When the V
hardware. The output of this comparator is connected to EXTI line 31 and it can be used to
generate an interrupt.
The device features an embedded programmable voltage detector (PVD) that monitors the
V power supply and compares it to the V
DD
when V
DD
threshold. The interrupt service routine can then generate a warning message and/or put
the MCU into a safe state. The PVD is enabled by software.
14/117
= 2.0 to 3.6 V: external power supply for I/Os and the internal regulator. Provided
pins.
DD
= 2.0 to 3.6 V: external analog power supply for ADC, Reset blocks, RCs and
= 1.65 to 3.6 V: external power supply for marked I/Os. Provided externally
, but it must not be provided without a valid supply on V
DDA
= 1.65 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and
, without the need for an external reset circuit.
should arrive first and be greater than or equal to V
DDA
.
DD
supply is monitored and compared with the internal reference voltage (V
is below this threshold, all the I/Os supplied from this rail are disabled by
DDIO2
drops below the V
PVD
DocID025832 Rev 2
is 2.4 V when the ADC is used). The V
DDA
voltage level is completely independent from V
DDIO2
DD
supply voltage. During the startup phase it is required
DD
and V supply voltages, however the V
DD DDA
threshold. An interrupt can be generated
PVD
threshold and/or when V
STM32F042xx
voltage level and must be
DD
. Refer to the pinout
DD
is not present.
.
DD
is higher than or
DDA
is higher than the V
DD
DDA
DD
power
DDA
).
REFINT
PVD