Hardware layout and configuration UM2407
24/49 UM2407 Rev 3
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 STLINK-V3E (default): MCO output of ST-LINK is used as an input clock.
This frequency cannot be changed. It is fixed at 8 MHz and connected to the PF0/PH0-
OSC_IN of the 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 its typical frequencies,
capacitors, and resistors, refer to the STM32H7 series microcontroller datasheet and
the application note Oscillator design guide for STM8AF/AL/S and STM32
microcontrollers (AN2867) for the oscillator design guide. The X3 crystal has the
following characteristics: 25 MHz, 6 pF, 20 ppm. The configuration must be:
– SB44 and SB46 OFF
– SB3 and SB4 ON
– C69 and C70 ON with 5.6 pF capacitors
–SB45 OFF
• Oscillator from external PF0/PH0: from an external oscillator through 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 clocks. The
configuration must be:
– SB44 and SB46 ON
–SB45 OFF
– SB3 and SB4 OFF
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