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 crystal (X3) (configuration depends on the embedded STM32U5 Series
microcontroller)
To help select the crystal and its associated capacitors (C59, C60), refer to the application note Oscillator design
guide for STM8AF/AL/S, STM32 MCUs and MPUs (AN2867).
As an example, the crystal (X3) might have the following characteristics: 16 MHz, 8 pF, and 20 ppm. It is then
recommended to use NX2016SA_16MHz_EXS00A-CS07826 manufactured by NDK.
In this case, configure the board as follow:
• SB47 and SB49 OFF. PH0 and PH1 are not connected to CN11 as I/Os.
• SB48 (MCO) OFF
• SB4 and SB5 ON are connected to external HSE.
MCO from STLINK-V3E (default: not connected):
The MCO output of STLINK-V3E 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:
• SB47 OFF and SB49 ON. Only PH1 can be connected to CN11 as I/O.
• SB48 ON. MCO is connected to PH0 and R5 on the STLINK-V3E side and must be connected to provide
the MCO to the STLINK-V3E output.
• SB4 and SB5 OFF. The external crystal is not connected to HSE.
• Resistor (R5) and capacitor (C5) can be adapted for the 8Mhz shape.
External oscillator to PH0 (default: not connected)
The input clock comes from an external clock through PH0, on expansion connector (CN11) pin 29. The following
configuration is needed:
• SB47 and SB49 ON. PH0 and PH1 are connected to CN11. PH1 can be used as a GPIO.
• SB48 OFF. MCO is not connected to PH0.
• SB4 and SB5 OFF. The external crystal (X3) is disconnected from PH0 and PH1.
HSE not used (configuration depends on the embedded STM32U5 Series microcontroller)
PH0 and PH1 are used as GPIOs instead of crystal inputs. The following configuration is needed:
• SB47 and SB49 ON. PH0 and PH1 are connected to the expansion connector (CN11) as GPIOs.
• SB48 OFF. MCO is not connected to PH0.
• SB4 and SB5 OFF. The external crystal (X3) is disconnected from PH0 and PH1.
6.8
Reset sources
The reset signal of the Nucleo board is active LOW and the reset sources come from:
• The RESET button (B2)
• The embedded STLINK-V3E
• The ARDUINO
®
-included Zio connector CN8 pin 5
• The ST morpho connector CN11 pin 14
UM2861
Reset sources
UM2861 - Rev 5
page 27/49
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