Osc Clock Sources; Lse: Osc 32 Khz Clock Supply; Hse: Osc Clock Supply - ST STM32U083C-DK User Manual

6.5

OSC clock sources

Two clock sources are available on the Discovery kit:
• LSE is the 32.768 kHz crystal for the STM32 embedded RTC
• HSE is the 24 MHz oscillator for the STM32 microcontroller. Not fitted by default.
To help select the crystals and their associated capacitors, refer to the application note Oscillator design guide for
STM8AF/AL/S, STM32 MCUs and MPUs (AN2867).
6.5.1

LSE: OSC 32 KHz clock supply

There are three ways to configure the pins corresponding to the low-speed clock (LSE):
LSE on-board oscillator X2 crystal (default configuration)
For example, the X2 crystal embedded in the Discovery kit has the following characteristics: 32.768 kHz, 6 pF,
and 20 ppm.
The use of the embedded X2 crystal requests the following SB configuration:
• SB16 and SB18 OFF
• R52 and R53 ON
External oscillator connected to PC14 input
The use of the external oscillator through pin 27 of the extension connector (CN7) requests the following
configuration:
• SB16 ON
• R52 and R53 OFF
LSE not used
PC14 and PC15 are used as GPIOs instead of low-speed clocks. The following configuration is needed:
• SB16 and SB18 ON
• R52 and R53 OFF
6.5.2

HSE: OSC clock supply

There are three ways to configure the pins corresponding to the external high‑speed clock (HSE):
HSE on-board oscillator from X3 crystal
For example, the X3 crystal embedded in the Discovery kit has the following characteristics: 24 MHz, 8 pF,
20 ppm. The use of the embedded X3 crystal requests the following solder bridge configuration:
• SB19 and SB20 OFF
• R54 and R55 ON
External oscillator to PF0 input
The input clock comes from an external oscillator through PF0 (CN17 pin 31). The following configuration is
needed:
• SB19 ON
• R54 and R55 OFF
HSE not used (default configuration)
PF0 and PF1 are used as GPIOs instead of clocks. The following configuration is needed:
• SB19 and SB20 ON
• R54 and R55 OFF
UM3292 - Rev 1
UM3292
Hardware layout and configuration
page 14/33