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Functional overview STM32L031x4/6

22/126 DS10668 Rev 6

internal reference voltage (V

REFINT

) in Stop mode. The device remains in reset mode when

is below a specified threshold, V

POR/PDR

or V

BOR

, without the need for any external

reset circuit.

Note: The start-up time at power-on is typically 3.3 ms when BOR is active at power-up, the start-

up time at power-on can be decreased down to 1 ms typically for devices with BOR inactive

at power-up.

The devices feature an embedded programmable voltage detector (PVD) that monitors the

DD/VDDA

power supply and compares it to the V

PVD

threshold. This PVD offers 7 different

levels between 1.85 V and 3.05 V, chosen by software, with a step around 200 mV. An

interrupt can be generated when V

DD/VDDA

drops below the V

PVD

threshold and/or when

DD/VDDA

is higher than the V

PVD

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.

3.4.3 Voltage regulator

The regulator has three operation modes: main (MR), low power (LPR) and power down.

• MR is used in Run mode (nominal regulation)

• LPR is used in the Low-power run, Low-power sleep and Stop modes

• Power down is used in Standby mode. The regulator output is high impedance, the

kernel circuitry is powered down, inducing zero consumption but the contents of the

registers and RAM are lost except for the standby circuitry (wakeup logic, IWDG, RTC,

LSI, LSE crystal 32 KHz oscillator, RCC_CSR).

3.4.4 Boot modes

At startup, BOOT0 pin and nBOOT1 option bit are used to select one of three boot options:

• Boot from Flash memory

• Boot from System memory

• Boot from embedded RAM

The boot loader is located in System memory. It is used to reprogram the Flash memory by

using SPI1 (PA4, PA5, PA6, PA7), USART2 (PA2, PA3) or USART2 (PA9, PA10). See

STM32™ microcontroller system memory boot mode AN2606 for details.

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