GD32F20x User Manual
67
Generally, digital circuits are powered by V
DD
, while most of analog circuits are powered by
V
DDA
. To improve the ADC and DAC conversion accuracy, the independent power supply
V
DDA
is implemented to achieve better performance of analog circuits. V
DDA
can be externally
connected to V
DD
through the external filtering circuit that avoids noise on V
DDA
, and V
SSA
should be connected to V
SS
through the specific circuit independently. If V
DDA
is different from
V
DD
, V
DDA
must always be higher, but the voltage difference should not exceed 0.2V.
To ensure a high accuracy on low voltage ADC and DAC, the separate external reference
voltage on V
REF
should be connected to ADC/DAC pins. According to the different packages,
V
REF+
pin must be connected to V
DDA
pin, V
REF-
pin must be connected to V
SSA
pin. The V
REF+
pin is only available on no less than 100-pin packages, or else the V
REF+
pin is not available
and internally connected to V
DDA.
The V
REF-
pin is only available on no less than 100-pin
packages, or else the V
REF-
pin is not available and internally connected to V
SSA
.
3.3.3.
1.2V power domain
The main function of 1.2V power domain includes Cortex
™
-M3 logic, AHB/APB peripherals,
the APB interfaces for the Backup domain and the
V
DD
/V
DDA
domain, etc. Once the 1.2V is
powered up, the POR will generate a reset sequence on the 1.2V power domain. If need to
enter the expected power saving mode, the associated control bits must be configured. Then,
once a WFI
(Wait for Interrupt)
or WFE
(Wait for Event)
instruction is executed, the device
will enter an expected power saving mode which will be discussed in the following section.
3.3.4.
Power saving modes
After a system reset or a power reset, the GD32F20x MCU operates at full function and all
power domains are active. Users can achieve lower power consumption through slowing
down the system clocks (HCLK, PCLK1, PCLK2) or gating the clocks of the unused
peripherals. Besides, three power saving modes are provided to achieve even lower power
consumption, they are Sleep mode, Deep-sleep mode, and Standby mode.
Sleep mode
The Sleep mode is corresponding to the SLEEPING mode of the
Cortex™-M3. In Sleep mode,
only clock of
Cortex™-M3 is off. To enter the Sleep mode, it is only necessary to clear the
SLEEPDEEP bit in the
Cortex™-M3 System Control Register, and execute a WFI or WFE
instruction. If the Sleep mode is entered by executing a WFI instruction, any interrupt can
wake up the system. If it is entered by executing a WFE instruction, any wakeup event can
wake up the system (If SEVONPEND is 1, any interrupt can wake up the system, refer to
Cortex-M3 Technical Reference Manual). The mode offers the lowest wakeup time as no time
is wasted in interrupt entry or exit.
According to the SLEEPONEXIT bit in the
Cortex™-M3 System Control Register, there are
two options to select the Sleep mode entry mechanism.
Sleep-now: if the SLEEPONEXIT bit is cleared, the MCU enters Sleep mode as soon as
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...