6.6 Push-buttons
Two buttons are available on the Nucleo board.
User button (B1)
The blue button for user and wake‑up functions is connected to PC13 to support the default TAMPER function
or to PA0 to support the optional wake‑up function of the STM32 microcontroller. When the button is pressed the
logic state is HIGH, otherwise, the logic state is LOW.
• To connect the USER button to PC13, SB58 must be ON and SB59 must be OFF. This is the default
configuration.
• To connect the USER button to PA0, SB58 must be OFF and SB59 must be ON. This is the optional
configuration.
Buttons are implemented using a hardware debounce filter combined with a serial resistor to avoid damaging the
STM32 GPIO in case of wrong GPIO setting. This 330 Ω serial resistor (R39) can be replaced by a 0 Ω resistor
assuming the GPIO configuration is properly done. The hardware debounce filter is composed of a 100 nF
capacitor (C84) with a 100 kΩ pull-down resistor (R38). Both components can be suppressed to reduce the BOM
cost assuming that the debounce is handled by firmware.
Warning: The PC13 I/O used for the user button must be set to INPUT, pull
‑
down (PD) with
debouncing. Never set the PC13 to OUTPUT / LOW level to avoid a shortcut when the
user button is pressed.
Reset button (B2)
The black button connected to NRST is used to reset the STM32 microcontroller. When the button is pressed the
logic state is LOW, otherwise, the logic state is HIGH.
The blue and black plastic hats placed on these push‑buttons can be removed if necessary when a shield or
an application board is plugged into the top of the Nucleo board. This avoids pressure on the buttons and
consequently a possible permanent target MCU reset.
UM2861
Push-buttons
UM2861 - Rev 5
page 25/49
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