ST STM32L152-EVAL - Figure 6. Reset Circuit; System Reset

AN3216 Power supplies
Doc ID 17496 Rev 5 13/30
2.3.4 System reset
A system reset sets all registers to their reset values except for the RTC, backup registers
and RCC control/status register, RCC_CSR.
A system reset is generated when one of the following events occurs:
1. A low level on the NRST pin (external reset)
2. Window watchdog end-of-count condition (WWDG reset)
3. Independent watchdog end-of-count condition (IWDG reset)
4. A reset bit set by software (SWreset)
5. Entering Standby or Stop mode configured to generate a reset (Low-power
management reset).
6. Option byte loader reset
7. Exiting Standby mode
The reset source can be identified by checking the reset flags in the Control/Status register,
RCC_CSR.
Figure 6. Reset circuit
The STM32L does not require an external reset circuit to power-up correctly. Only a pull-
down capacitor is recommended to improve EMS performance by protecting the device
against parasitic resets (see Figure 6).
Charging/discharging the pull-down capacitor thru the internal resistor adds to the device
power consumption. The recommended value of 100 nF for the capacitor can be reduced to
10 nF to limit this power consumption.
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