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7.9 Clock references
Two clock references are available on STM32U575I-EV for the STM32U575AII6Q target microcontroller.
•
32.768 kHz crystal X2, for LSE embedded RTC
• 16 MHz crystal X1, for HSE clock generator.
The main clock can also be generated using an internal RC oscillator.
Table 17 describes the hardware configuration for the LSE 32.768 kHz.
Table 17. Hardware I/O configuration for the 32.768 kHz
I/O
Solder
bridge
Setting
(1) Comment
PC14 SB87
OFF
X2 is used as a clock reference with connected R27.
PC14 OSC32_IN terminal is not routed to the CN9 extension connector.
ON
PC14 OSC32_IN is routed to the CN9 extension connector.
R27 must be removed from the X2 crystal circuit to not disturb clock
reference, clock source from the daughterboard, or PC14 IO function.
PC15 SB86
OFF
X2 is used as a clock reference with connected R28.
PC15 OSC32_OUT terminal is not routed to the CN9 extension
connector.
ON
PC15 OSC32_OUT is routed to the CN9 extension connector.
R28 must be removed from the X2 crystal circuit to not disturb clock
reference, clock source from the daughterboard, or PC15 IO function.
1. The default configuration is shown in bold.
Refer to the application note Oscillator design guide for STM8AF/AL/S, STM32 MCUs and MPUs ( AN2867 ) with
the following characteristics: 32.768 kHz, 9 pF, 20 ppm.
Table 18 describes the hardware configuration for the 16 MHz HSE clock.
Table 18. Hardware I/O configuration for the 16 MHz HSE clock
I/O
Solder
bridge
Setting
(1) Comment
PH0
SB89
OFF
X1 can be used as a clock reference with connected R25.
PH0 OSC_IN terminal is not routed to the CN10 extension connector.
SB90 for MCO must be open.
ON
PH0 OSC_IN is routed to the CN10 extension connector.
R25 and SB90 must be removed to not disturb clock reference, clock source
on the daughterboard, or PH0 IO function.
SB90
OFF
PH0 OSC_IN terminal is not connected to STLINK-V3 MCO clock
reference.
ON
PH0 OSC_IN is connected to STLINK MCO clock reference.
R25 and SB89 must be removed to not disturb the MCO clock reference.
PH1 SB88
OFF
X1 can be used as a clock reference with connected R26.
PH1 OSC_OUT terminal is not routed to the CN10 extension connector.
ON
PH1 OSC_OUT is routed to the CN10 extension connector.
R26 must be removed, in order not to disturb clock reference, clock source on
the daughterboard, or PH1 IO function.
1. The default configuration is shown in bold.
STM32U575I-EV
Clock references
UM2854 - Rev 1
page 35/105