GD32W51x User Manual
133
The clock source of the Real Time Clock (RTC) circuit can be derived from the Internal 32KHz
RC oscillator (IRC32K) or the Low Speed Crystal oscillator (LXTAL), or HXTAL clock divided
by 2 to 31. 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
®
-M33 can setup the RTC
register with an expected alarm time and enable the alarm function and according EXTI lines
to achieve the RTC alarm event. After entering the power saving mode for a certain amount
of time, the RTC alarm will wake up the device when the time match event occurs. The details
of the RTC configuration and operation will be described in the
When the Backup domain is supplied by V
DD
(V
BAK
pin is connected to V
DD
), the following
function is available:
PC14 and PC15 can be used as either GPIO or LXTAL Crystal oscillator pins.
When the Backup domain is supplied by V
BAT
(V
BAK
pin is connected to V
BAT
), the following
function is available:
PC14 and PC15 can be used as LXTAL Crystal oscillator pins only.
Note
:
Since PC14 and PC15 are supplied through the Power Switch, which can only be
obtained by a small current, the speed of GPIOs PC14 to PC15 should not exceed 2MHz
when they are in output mode (maximum load: 30pF).
5.3.2.
VDD / VDDA power domain
V
DD
/ V
DDA
domain includes two parts: V
DD
domain and V
DDA
domain. V
DD
domain includes
HXTAL (High Speed Crystal oscillator), LDO (Voltage Regulator), POR / PDR (Power On /
Down Reset), FWDGT (Free Watchdog Timer), all pads except PC14 / PC15, etc. V
DDA
domain includes ADC (AD Converter), IRC16M (Internal 16MHz RC oscillator), IRC32K
(Internal 32KHz RC oscillator), PLLs (Phase Locking Loop), LVD (Low Voltage Detector), etc.
V
DD
domain
The LDO, which is implemented to supply power for the 1.2V domain, is always enabled after
reset. It can be configured to operate in three different status, including in the Sleep mode
(full power on), in the Deep-sleep mode (on or low power), and in the Standby mode (power
off).
The POR / PDR circuit is implemented to detect V
DD
/ V
DDA
and generate the power reset
signal which resets the whole chip except the Backup domain when the supply voltage is
lower than the specified threshold.
Figure 4-4. Waveform of the POR / PDR
relationship between the supply voltage and the power reset signal. V
POR
, which typical value
is 1.54V, indicates the threshold of power on reset, while V
PDR
, which typical value is 1.50V,
means the threshold of power down reset. The hysteresis voltage (V
hyst
) is around 40mV.