3.3.1. Backup domain
The Backup domain is powered by the V
DD
or the battery power source (V
BAT
) selected by the
internal power switch, and the V
BAK
pin which drives Backup Domain, power supply for RTC
unit, LXTAL oscillator, BPOR，and three BKP PAD including PC13 to PC15. In order to
ensure the content of the Backup domain registers and the RTC supply, when V
DD
supply is
shut down, V
BAT
pin can be connected to an optional standby voltage supplied by a battery or
by another source. The power switch is controlled by the Power Down Reset circuit in the
V
DD
/ V
DDA
domain. If no external battery is used in the application, it is recommended to
connect V
BAT
pin externally to V
DD
pin with a 100nF external ceramic decoupling capacitor.
The Backup domain reset sources include the Backup domain power-on-reset (BPOR) and
the Backup Domain software reset. The BPOR signal forces the device to stay in the reset
mode until V
BAK
is completely powered up. Also the application software can trigger the
Backup domain software reset by setting the BKPRST bit in the RCU_BDCTL register to
reset the Backup domain.
The clock source of the Real Time Clock (RTC) circuit can be derived from the Internal
40KHz RC oscillator (IRC40K) or the Low Speed Crystal oscillator (LXTAL), or HXTAL clock
divided by 32. When V
DD
is shut down, only LXTAL is valid for RTC. Before entering the
power saving mode by executing the WFI / WFE instruction, the Cortex
®
-M4 can setup the
RTC register with an expected alarm time and enable the alarm function and according EXTI
To Next Page
Loading...
