UM2407 Rev 1 25/48
UM2407 Hardware layout and configuration
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6.5 Clock sources
6.5.1 HSE clock (high speed external clock)
There are four ways to configure the pins corresponding to the external high-speed clock
(HSE):
• MCO from ST-LINK (default): MCO output of ST-LINK is used as input clock. This
frequency cannot be changed, it is fixed at 8 MHz and connected to the PF0/PH0-
OSC_IN of STM32H7 Series microcontroller. The configuration must be:
– SB44 and SB46 OFF
–SB45 ON
– SB3 and SB4 OFF
• HSE on-board oscillator from X3 crystal (not provided): for typical frequencies and its
capacitors and resistors, refer to the STM32H7 Series microcontroller data sheet and
to the Oscillator design guide for STM8AF/AL/S and STM32 microcontrollers
Application note (AN2867) for the oscillator design guide. The X3 crystal has the
following characteristics: 25 MHz, 6 pF, 20 ppm. It is recommended to use
NX2016SA-25MHz-EXS00A-CS11321 manufactured by NDK. The configuration must
be:
– SB44 and SB46 OFF
– SB3 and SB4 ON
– C69 and C70 soldered with 5.6 pF capacitors
–SB45 OFF
Oscillator from external PF0/PH0: from an external oscillator through the pin 29 of the CN11
connector. The configuration must be:
–SB46 ON
–SB45 OFF
– SB3 and SB4 OFF
• HSE not used: PF0/PH0 and PF1/PH1 are used as GPIOs instead of as clock. The
configuration must be:
– SB44 and SB46 ON
–SB45 OFF
– SB3 and SB4 OFF
6.5.2 LSE clock (low-speed external clock) - 32.768 kHz
There are three ways to configure the pins corresponding to low-speed clock (LSE):
• On-board oscillator (default): X2 crystal. Refer to the Oscillator design guide for
STM8AF/AL/S and STM32 microcontrollers Application note (AN2867) for oscillator
design guide for STM32H7 Series microcontrollers. It is recommended to use
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