Datasheet

DocID022691 Rev 4 15/131
STM32F37xxx Functional overview
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3.7.4 Low-power modes
The STM32F373x supports 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 the lowest 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 line. The EXTI line
source can be one of the 16 external lines, the PVD output, the USARTs, the I2Cs, the
CEC, the USB wakeup, and the RTC alarm.
• 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 Backup
domain and Standby circuitry.
The device exits Standby mode when an external reset (NRST pin), an IWDG reset, a
rising edge on the WKUP pin, or an RTC alarm occurs.
Note: The RTC, the IWDG, and the corresponding clock sources are not stopped by entering Stop
or Standby mode.
3.8 Clocks and startup
System clock selection is performed on startup, however the internal RC 8 MHz oscillator is
selected as default CPU clock on reset. An external 4-32 MHz clock can be selected, in
which case it is monitored for failure. If failure is detected, the system automatically switches
back to the internal RC oscillator. A software interrupt is generated if enabled. Similarly, full
interrupt management of the PLL clock entry is available when necessary (for example with
failure of an indirectly used external oscillator).
Several prescalers allow to configure the AHB frequency, the high speed APB (APB2) and
the low speed APB (APB1) domains. The maximum frequency of the AHB and the high
speed APB domains is 72 MHz, while the maximum allowed frequency of the low speed
APB domain is 36 MHz.
3.9 General-purpose input/outputs (GPIOs)
Each of the GPIO pins can be configured by software as output (push-pull or open-drain), as
input (with or without pull-up or pull-down) or as peripheral alternate function. Most of the
GPIO pins are shared with digital or analog alternate functions. All GPIOs are high current
capable except for analog inputs.
The I/Os alternate function configuration can be locked if needed following a specific
sequence in order to avoid spurious writing to the I/Os registers.