Osc Clock Sources; Lse: Osc 32 Khz Clock Supply; Osc Clock Supply - ST STM32U5 Nucleo-64 User Manual

6.7

OSC clock sources

Three clock sources are available on the Nucleo-64 board:
• LSE is the 32.768 kHz crystal for the STM32 embedded RTC.
• MCO is the 8 MHz clock from STLINK-V3E MCU for the STM32 microcontroller.
• HSE is the 16 MHz oscillator for the STM32 microcontroller. This clock is available depending on the target
STM32 Series microcontroller used on the Nucleo-64 board.
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).
6.7.1

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 X3 crystal (default configuration)
For example, the X3 crystal embedded in the Nucleo-64 has the following characteristics: 32.768 kHz, 9 pF,
20 ppm, and reference NX1610SE‑ 32.768KHZ‑EXS00A‑ MU01499 manufactured by NDK.
To use the embedded X3 crystal, the following SB configuration is needed:
• SB1 and SB2 ON
• SB18 and SB22 OFF
External oscillator connected to PC14 input
From the external oscillator through pin 25 of the ST morpho connector (CN7). The following configuration is
needed:
• SB1 and SB2 OFF
• SB18 and SB22 ON, for connection from ST morpho connector CN7 pin 25
LSE not used
PC14 and PC15 are used as GPIOs instead of low‑speed clocks. The following configuration is needed:
• SB1 and SB2 OFF
• SB18 and SB22 ON
6.7.2

OSC clock supply

There are four ways to configure the pins corresponding to the external high‑speed clock (HSE):
HSE: on-board oscillator X2 crystal (default: not connected)
For example, the X2 crystal embedded in the Nucleo-64 has the following characteristics: 16 MHz, 8 pF, 20 ppm.
The reference is NX2016SA_16MHz_EXS00A-CS07826 manufactured by NDK.
To use the embedded X2 crystal, the following SB configuration is needed:
• SB19 and SB21 OFF. PH0 and PH1 are not connected to CN7 as I/O.
• SB20 (MCO) OFF
• SB3 and SB4 ON are connected to use the external crystal.
MCO from STLINK-V3EC (default: not connected):
The MCO output of STLINK-V3EC MCU is used as an input clock. This frequency cannot be changed. It is fixed
at 8 MHz and connected to PH0 OSC_IN of the STM32 microcontroller. To use this clock source, the following
configuration is needed:
• SB19 OFF and SB21 ON. Only PH1 can be connected to CN7 as I/O.
• SB20 ON: MCO is connected to PH0 and R8 on the STLINK-V3EC side must be connected to provide the
MCO from the STLINK-V3EC output. The resistor (R7) and capacitor (C6) can be adapted for the 8 Mhz
shape. SB20 OFF.
• SB3 and SB4 OFF. The external crystal is disconnected from PH0 and PH1.
UM3062 - Rev 1
UM3062
OSC clock sources
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