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STM32L4 Standby Mode GPIO State {Schmitt Trigger} Clarification from Reference Manual


I am designing an UltraLow-Power product around the MCU STM32L412. I need to help clarifying the GPIO states during Standby. Specifically, if the Schmitt trigger is ON or OFF during Standby. This will impact my electrical design if I need to have external Pullup/Pulldowns on some pins to prevent current leakage during Standby. The Reference Manual {which Overall is fantastic} has what appears to be inconsistent info regarding this issue. I am hoping for an ST employee to clarify.


FROM: RM0394 Reference Manual STM32L41xxx/........

5.3.10 Shutdown mode

I/O states in Shutdown mode

In the Shutdown mode, are by default in floating state. If the APC bit of PWR_CR3 register

has been set, the I/Os can be configured either with a pull-up (refer to PWR_PUCRx

registers (x=A,B,C,D,E,F,G,H), or with a pull-down (refer to PWR_PDCRx registers

(x=A,B,C,D,E,F,G,H)), or can be kept in analog state if none of the PWR_PUCRx or

PWR_PDCRx register has been set. The pull-down configuration has highest priority over

pull-up configuration in case both PWR_PUCRx and PWR_PDCRx are set for the same IO.

However this configuration is lost when exiting the Shutdown mode due to the power-on


It appears the authors stated that by default pins are floating state {which to me implies Schmitt trigger is ON} then later in paragraph states that if PWR_CR3 register is not used AND if no pullup or pulldown set then pins are kept in analog state {which to me implies Schmitt trigger is OFF}

If an ST employee can please clarify if I can indeed set GPIOs in Standby with Schmitt trigger OFF as I have several pins, I prefer to have no external components and would leave floating voltage on the pins during standby.

QUESTION2: Similar question but specific for PB3

from Reference manual I understand the Debug pins in Standby will be

• PA15: JTDI in pull-up

• PA14: JTCK/SWCLK in pull-down

• PA13: JTMS/SWDAT in pull-up

• PB4: NJTRST in pull-up

• PB3: JTDO in floating state no pull-up/pull-down

For PB3 will the Schmitt trigger be ON or OFF by default in Standby? And is there any option to turn OFF if it is ON by default?

I understand if Schmitt trigger is always ON for PB3 in Standby then I will need to add an external pulldown/pullup resistor to prevent current leakage due to the floating volts affecting the trigger. I would prefer to avoid adding external components if not necessary.


John Russell

Design Engineer

Simon V.
ST Employee

Hello John,

Did you found the material which answer your questions since you have post this message or do you need help ?



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