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Rev. 1.00
82 of 576
January 28, 2022
32-Bit Arm
®
Cortex
®
-M0+ MCU
HT32F54231/HT32F54241/HT32F54243/HT32F54253
6 Clock Control Unit (CKCU)
Features
▆
4 ~ 16 MHz external crystal oscillator (HSE)
▆
Internal 8 MHz RC oscillator (HSI) with configuration option calibration and custom trimming
capability
▆
PLL with selectable clock source (from HSE or HSI) for system clock
▆
32,768 Hz external crystal oscillator (LSE) for Watchdog Timer, RTC or system clock
▆
Internal 32 kHz RC oscillator (LSI) for Watchdog Timer, RTC or system clock
▆
HSE clock monitor
Functional Descriptions
High Speed External Crystal Oscillator – HSE
The high speed external 4 to 16 MHz crystal oscillator (HSE) produces a highly accurate
clock source to the system clock. The related hardware configuration is shown in the following
figure. The crystal with specific frequency must be placed across the two HSE pins (XTALIN /
XTALOUT) and the external components such as resistors and capacitors are necessary to make it
oscillate properly.
The following guidelines are provided to improve the stability of the crystal circuit PCB layout.
▆
The crystal oscillator should be located as close as possible to the MCU so that the trace lengths
are kept as short as possible to reduce any parasitic capacitances.
▆
Shield any lines in the vicinity of the crystal by using a ground plane to isolate signals and reduce
noise.
▆
Keep frequently switching signal lines away from the crystal area to prevent crosstalk.
Crystal
C
L1
C
L2
XTALOUT
XTALIN
OSC_EN
4 MHz ~ 16 MHz
Figure 16. External Crystal, Ceramic and Resonators for HSE