Cyclic Redundancy Check Calculation Unit (Crc); Power Management; Power Supply Schemes; Power Supply Supervisors - STMicroelectronics STM32F042F4 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
regulator. It is provided externally through VDD pins.
• V
DDA
and PLL (minimum voltage to be applied to V
provided externally through VDDA pin. The V
or equal to the V
•
V
DDIO2
externally through the VDDIO2 pin. The V
from V
V
DDIO2
(V
REFINT
are disabled by hardware. The output of this comparator is connected to EXTI line 31
and it can be used to generate an interrupt. Refer to the pinout diagrams or tables for
concerned I/Os list.
•
V
BAT
backup registers (through power switch) when V
For more details on how to connect power pins, refer to
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 device features an embedded programmable voltage detector (PVD) that monitors the
V power supply and compares it to the V
DD
when V
DD
14/117
= V = 2.0 to 3.6 V: external power supply for I/Os (V
DDIO1
= from V to 3.6 V: external analog power supply for ADC, Reset blocks, RCs
DD
voltage level and must be established first.
DD
= 1.65 to 3.6 V: external power supply for marked I/Os. V
or V , but it must not be provided without a valid supply on V
DD DDA
supply is monitored and compared with the internal reference voltage
). When the V
DDIO2
= 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
drops below the V
PVD
DocID025832 Rev 5
is 2.4 V when the ADC is used). It is
DDA
voltage level must be always greater
DDA
voltage level is completely independent
DDIO2
is below this threshold, all the I/Os supplied from this rail
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
STM32F042x4 STM32F042x6
) and the internal
DDIO1
is provided
DDIO2
is not present.
Figure 13: Power supply
.
DD
is higher than or
DDA
is higher than the V
DD
. The
DD
scheme.
power
DDA
PVD