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Rev. 1.00
86 of 576
January 28, 2022
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F54231/HT32F54241/HT32F54243/HT32F54253
6 Clock Control Unit (CKCU)
Table 17. Feedback Divider 2 Value Mapping
Feedback Divider 2 Setup Bits B3 ~ B0
(PFBD Field in the PLLCFGR Register)
NF2
(Feedback Divider 2 Value)
0000
16
0001
1
0010
2
0011
3
0100
4
0101
5
0110
6
0111
7
1000
8
1001
9
1010
10
1011
11
1100
12
:
:
:
:
1111
15
Low Speed External Crystal Oscillator – LSE
The low speed external crystal or ceramic resonator oscillator with a 32,768 Hz frequency produces
a low power but highly accurate clock source for the circuits of Real-Time-Clock peripheral,
Watchdog Timer or system clock. The associated hardware configuration is shown in the following
figure. The crystal or ceramic resonator must be placed across the two LSE pins (X32KIN /
X32KOUT) and the external components such as resistors and capacitors are necessary to make it
oscillate properly. The LSE oscillator can be switched on or off by using the LSEEN bit in the RTC
Control Register (RTCCR). The LSERDY flag in the Global Clock Status Register (GCSR) will
indicate if the LSE clock is stable.
X32KOUT
C
L2
32.768 kHz
X32KIN
C
L1
Figure 19. External Crystal, Ceramic and Resonators for LSE