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Rev. 1.00
88 of 576
January 28, 2022
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F54231/HT32F54241/HT32F54243/HT32F54253
6 Clock Control Unit (CKCU)
HSE Clock Monitor
The main function of the oscillator check is enabled by the HSE Clock Monitor Enable bit CKMEN
in the Global Clock Control Register (GCCR). The HSE clock monitor should be enabled after the
HSE oscillator start-up delay and be disabled when the HSE oscillator is stopped. Once the HSE
oscillator failure is detected, the HSE oscillator will automatically be disabled. The HSE clock
stuck flag CKSF in the Global Clock Interrupt Register (GCIR) will be set and an interrupt of main
oscillator failure will be generated if the clock stuck interrupt enable bit CKSIE in the GCIR is set.
This failure interrupt is connected to the exception vector of CPU Non-Maskable Interrupt (NMI).
If the HSE is directly used as the system clock source, when the HSE oscillator failure occurs,
the HSE will be turned off and the system clock will be switched to the HSI automatically by the
hardware. If the HSE is used as the clock input of the PLL circuit and the system clock comes from
the PLL circuit output, the PLL circuit will also be turned off as well as the HSE when the failure
happens.
Clock Output Capability
The device has the clock output capability to allow the clocks to be output on the specific external
output pin CKOUT. The configuration registers of the corresponding GPIO port must be well
configured in the Alternate Function I/O section, AFIO, to output the selected clock signal. There
are seven output clock signals to be selected via the device clock output source selection field
CKOUTSRC in the Global Clock Configuration Register (GCFGR).
Table 18. CKOUT Clock Source
CKOUTSRC[2:0]
Clock Source
000
CK_REF = CK_PLL / (CK 1) / 2
001
HCLKC / 16
010
CK_SYS / 16
011
CK_HSE / 16
100
CK_HSI / 16
101
CK_LSE
110
CK_LSI