STM32F042C4 datasheet(15/117 Pages) STMICROELECTRONICS

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STM32F042x4 STM32F042x6

Functional overview

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.

3.5.3

Voltage regulator

The regulator has two operating modes and it is always enabled after reset.

•

Main (MR) is used in normal operating mode (Run).

•

Low power (LPR) can be used in Stop mode where the power demand is reduced.

In Standby mode, it is put in power down mode. In this mode, the regulator output is in high

impedance and the kernel circuitry is powered down, inducing zero consumption (but the

contents of the registers and SRAM are lost).

3.5.4

Low-power modes

The STM32F042x4/x6 microcontrollers support three low-power modes to achieve the best

compromise between low power consumption, short startup time and available wakeup

sources:

•

Sleep mode

In Sleep mode, only the CPU is stopped. All peripherals continue to operate and can

wake up the CPU when an interrupt/event occurs.

•

Stop mode

Stop mode achieves very low power consumption while retaining the content of SRAM

and registers. All clocks in the 1.8 V domain are stopped, the PLL, the HSI RC and the

HSE crystal oscillators are disabled. The voltage regulator can also be put either in

normal or in low power mode.

The device can be woken up from Stop mode by any of the EXTI lines. The EXTI line

source can be one of the 16 external lines, the PVD output, RTC, I2C1 USART1, USB

or the CEC.

The CEC, USART1 and I2C1 peripherals can be configured to enable the HSI RC

oscillator so as to get clock for processing incoming data. If this is used when the

voltage regulator is put in low power mode, the regulator is first switched to normal

mode before the clock is provided to the given peripheral.

•

Standby mode

The Standby mode is used to achieve the lowest power consumption. The internal

voltage regulator is switched off so that the entire 1.8 V domain is powered off. The

PLL, the HSI RC and the HSE crystal oscillators are also switched off. After entering

Standby mode, SRAM and register contents are lost except for registers in the RTC

domain and Standby circuitry.

The device exits Standby mode when an external reset (NRST pin), an IWDG reset, a

rising edge on the WKUP pins, or an RTC event occurs.

Note:

The RTC, the IWDG, and the corresponding clock sources are not stopped by entering Stop

or Standby mode.

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