
Rev. 1.00
92 of 576
January 28, 2022
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F54231/HT32F54241/HT32F54243/HT32F54253
6 Clock Control Unit (CKCU)
Bits
Field
Descriptions
[8]
HSEGAIN
External High Speed Clock Gain Selection
0: HSE low gain mode
1: HSE high gain mode
[2:0]
SW
System Clock Switch
00x: CK_PLL clock out as system clock
010: CK_HSE as system clock
011: CK_HSI as system clock
110: CK_LSE as system clock
111: CK_LSI as system clock
Others: CK_HSI as system clock
These bits are used to select the CK_SYS source. If the HSE oscillator is used
directly or indirectly as the system clock and the HSE clock monitor function is
enabled, once the HSE failure is detected, these bits will be set by hardware to force
HSI (b011) as the system clock.
Note: When switching the system clock using the SW field, the system clock will
not be immediately switched and a certain delay is necessary. Software can
monitor the CKSWST field in the clock source status register CKST to make
sure which clock is currently used as the system clock.
Global Clock Status Register – GCSR
This register indicates the clock ready status.
Offset:
0x008
Reset value: 0x0000_0028
31
30
29
28
27
26
25
24
Reserved
Type/Reset
23
22
21
20
19
18
17
16
Reserved
Type/Reset
15
14
13
12
11
10
9
8
Reserved
Type/Reset
7
6
5
4
3
2
1
0
Reserved
LSIRDY
LSERDY
HSIRDY
HSERDY
PLLRDY
Reserved
Type/Reset
RO 1 RO 0 RO 1 RO 0 RO 0
Bits
Field
Descriptions
[5]
LSIRDY
Internal Low Speed Clock Ready Flag
0: Internal 32 kHz RC oscillator clock is not ready
1: Internal 32 kHz RC oscillator clock is ready
Set by hardware to indicate that the LSI is stable to be used.
[4]
LSERDY
External Low Speed Clock Ready Flag
0: External 32,768 Hz crystal oscillator clock is not ready
1: External 32,768 Hz crystal oscillator clock is ready
Set by hardware to indicate that the LSE is stable to be used.