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Nations Technologies Inc.
Tel
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+86-755-86309900
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Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
4.2.4
STANDBY mode
STANDBY mode is a Cortex®-M4 based Deep-Sleep mode. The core domain is completely closed, and the backup
region is open to supply power to BKR.
Enter STANDBY mode
When entering STANDBY mode. The main difference is to set SCB_SCR.SLEEPDEEP=1, PWR_CTRL.PDS=1.
In STANDBY mode, all I/O pins remain high impedance except NRST, PA0_WKUP, PC13_TAMPER, PC14, PC15.
If an operation is in progress on FLASH, the time to enter STANDBY mode will be delayed until the memory access
is complete.
If an access to the APB area is in progress, the time to enter STANDBY mode will be delayed until the APB access
is complete.
In STANDBY mode, the following features can be selected by programming individual control bits:
Independent Watchdog (IWDG) optional: Once enabled, it will keep counting until a reset is generated.
RTC optional: It can be turned on by RCC_BDCTRL.RTCEN.
Internal RC oscillator (LSI RC) optional: It can be turned on by RCC_CTRLSTS.LSIEN.
External 32.768kHz crystal oscillator (LSE OSC) optional: It can be turned on by RCC_BDCTRL.LSEEN bit.
R-SRAM data retention, which can be turned on by register PWR_CTRL2.SR2STBRET.
Exit STANDBY mode
MCU exits STANDBY mode when an external reset (NRST pin), IWDG reset, rising edge of the WKUP pin, or a
rising edge of the RTC alarm event occurs. Except for the power status register (PWR_CTRLSTS), all registers are
reset after waking up from STANDBY state.
After waking up from STANDBY mode, code execution is the same as reset (detecting BOOT pin, getting reset
vector, etc.). The PWR_CTRLSTS.SBF status flag indicates that the MCU exits STANDBY mode.
4.2.5
VBAT mode
In VBAT mode the CPU is turned off, all peripherals are turned off, the main voltage regulator is turned off, the
LSE/LSI is configurable, and the HSE/HSI/PLL is turned off. Except for NRST/PC13-TAMPER/PC14-
OSC32_IN/PC15-OSC32_OUT, most IO ports are in high impedance state.
In VBAT mode, depending on the configuration before VDD is powered down, the following features are available:
RTC optional: It can be turned on by RCC_BDCTRL.RTCEN.
Internal RC oscillator (LSI RC) optional: It can be turned on by RCC_CTRLSTS.LSIEN.
External 32.768kHz crystal oscillator (LSE OSC) optional: It can be turned on by RCC_BDCTRL.LSEEN bit.
R-SRAM data retention, which can be turned on by register PWR_CTRL2.SR2STBRET.