ST STM32G0 1 Series Reference Manual page 121

RM0444
Warning:
If no external battery is used in the user application, it is recommended to connect VBAT pin
externally to VDD/VDDA pin with a 100 nF external ceramic decoupling capacitor.
When the RTC domain is supplied by V
pin functions are available:
When the RTC domain is supplied by V
is not present), only the following functions are available:
•
PC13, PC14 and PC15 can be controlled only by RTC, TAMP or LSE (refer to
Section 30.3: RTC functional
•
RTC_OUT1 function on PC13
•
RTC_TS function on PC13 or PA4
•
TAMP_IN1 function on PC13 or PA4 and TAMP_IN2 function on PA0
Note: Due to the fact that the power switch can transfer only a limited amount of current (3 mA),
the use of GPIO PC13 to PC15 in output mode is restricted: the speed has to be limited to
2 MHz with a maximum load of 30 pF and these I/Os must not be used as a current source
(e.g. to drive a LED).
RTC domain access
After a system reset, the RTC domain (RTC registers and backup registers) is protected
against possible unwanted write accesses. To enable access to the RTC domain, proceed
as follows:
1. Enable the power interface clock by setting the PWREN bits of the
clock enable register 1
2. Set the DBP bit of the
RTC domain.
3. Select the RTC clock source in the
4. Enable the RTC clock by setting the RTCEN bit in the
(RCC_BDCR).
During (temporization at V
t
RSTTEMPO
has been detected, the power switch between V
remains connected to V
During the startup phase, if V
t (refer to the datasheet for the value of t
RSTTEMPO
and V > V + 0.6 V, a current may be injected into V
DD BAT
through an internal diode connected between V
power switch (V ).
BAT
If the power supply/battery connected to the VBAT pin cannot
support this current injection, it is recommended to connect
an external low-drop diode between this power supply and
the VBAT pin.
DD
BAT
description)
(RCC_APBENR1).
Power control register 1 (PWR_CR1)
RTC domain control register
RM0444 Rev 5
startup) or after a PDR
DD
.
BAT
is established in less than
DD
(power switch connected to V
(power switch connected to V
RTC domain control register
Power control (PWR)
and V
BAT DD
)
RSTTEMPO
BAT
and the
DD
), all the related
DD
because V
BAT
APB peripheral
to enable access to the
(RCC_BDCR).
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DD
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