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RM0367 Rev 7 173/1043

RM0367 Reset and clock control (RCC)

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7 Reset and clock control (RCC)

7.1 Reset

There are three types of reset, defined as system reset, power reset and RTC domain reset.

7.1.1 System reset

A system reset sets all registers to their reset values unless specified otherwise in the

A system reset is generated when one of the following events occurs:

• A low level on the NRST pin (external reset)

• Window watchdog end-of-count condition (WWDG reset)

• Independent watchdog end-of-count condition (IWDG reset)

• A software reset (SW reset) (see Software reset)

• Low-power management reset (see Low-power management reset)

• Option byte loader reset (see Option byte loader reset)

• Exit from Standby mode

• Firewall protection (see Section 5: Firewall (FW))

The reset source can be identified by checking the reset flags in the control/status register,

RCC_CSR (see Section 7.3.21).

Software reset

The SYSRESETREQ bit in Cortex

-M0+ AIRCR register (Application Interrupt and Reset

Control Register) must be set to force a software reset on the device. Refer to Arm

Cortex

-M0+ Technical Reference Manual for more details.

Low-power management reset

There are two ways to generate a low-power management reset:

• Reset generated when entering Standby mode:

This type of reset is enabled by resetting nRST_STDBY bit in user option bytes. In this

case, whenever a Standby mode entry sequence is successfully executed, the device

is reset instead of entering Standby mode.

• Reset when entering Stop mode:

This type of reset is enabled by resetting nRST_STOP bit in user option bytes. In this

case, whenever a Stop mode entry sequence is successfully executed, the device is

reset instead of entering Stop mode.

Option byte loader reset

The Option byte loader reset is generated when the OBL_LAUNCH bit (bit 18) is set in the

FLASH_PECR register. This bit is used to launch by software the option byte loading.

For further information on the user option bytes, refer to Section 3: Flash program memory

and data EEPROM (FLASH).

ST STM32L0x3 User Manual

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