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Rev. 1.00
62 of 486
July 31, 2018
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F50231/HT32F50241
5 Power Control Unit (PWRCU)
5 Power Control Unit (PWRCU)
Hysteresis
V
POR
Time
V
DD
V
PDR
t
RSTD
POR Delay Time
RESET
Figure 12. Power On Reset / Power Down Reset Waveform
Low Voltage Detector / Brown Out Detector
The Low Voltage Detector, LVD, can detect whether the supply voltage V
DD
is lower than a
programmable threshold voltage V
LVD
. It is selected by the LVDS bits in the LVDCSR register.
When a low voltage on the VDD power pin is detected, the LVDF flag will be active and an
interrupt will be generated and sent to the MCU core if the LVDEN and LVDIWEN bits in the
LVDCSR register are set. For more details concerning the LVD programmable threshold voltage
V
LVD
, refer to the electrical characteristics of the corresponding datasheet.
The Brown Out Detector, BOD, is used to detect if the V
DD
supply voltage is equal to or lower
than V
BOD
. When the BODEN bit in the LVDCSR register is set to 1 and the V
DD
supply voltage
is lower than V
BOD
then the BODF flag is active. The PWRCU will regard this as a power down
reset situation and then immediately issue a system reset when the BODRIS bit is cleared to 0 or
issue an interrupt to notify the CPU to execute a power down procedure when the BODRIS bit is
set to 1. For more details concerning the Brown Out Detector voltage V
BOD
, refer to the electrical
characteristics of the corresponding datasheet.
High Speed External Oscillator
The High Speed External Oscillator, HSE, is located in the V
DD
power domain. The HSE crystal
oscillator can be switched on or off using the HSEEN bit in the Global Clock Control Register
(GCCR). The HSE clock can be used directly as the system clock source.
LSE, LSI and RTC
The Real Time Clock Timer clock source can be derived from either the Low Speed Internal RC
oscillator, LSI, or the Low Speed External Crystal oscillator, LSE. Before entering the power
saving mode by executing WFI / WFE instruction, the MCU needs to setup the compare register
with an expected wakeup time and enable the wakeup function to achieve the RTC timer wakeup
event. After entering the power saving mode for a certain amount of time, the Compare Match
flag, CMFLAG, will be asserted to wake up the device when the compare match event occurs. The
details of the RTC configuration for wakeup timer will be described in the RTC chapter.