Why is PA4 by default input when all other pins (except SWCLK and SWDIO) are analog?

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On the STM32L072 series, the reset state of all the pins are "Analog mode", except for PA4, PA13 (SWDIO) and PA14 (SWCLK).

When I put the STM32 into STOP mode, PA4 (configured as an input) causes the current consumption to increase by ~10uA. When I configure it as analog, the current consumption goes down to an acceptable 1.7uA (with 32 kHz crystal running).

I would like to know why PA4 is configured as an input after reset. One of it's alternative functions are "DAC_OUT1"... could this be the reason?

Thanks in advance,

Pieter

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Amel NASRIBest answer

ST Technical Moderator

Hi @Pieter Conradie ,

In the footnote of the pinout table, we mention that PA4 is a "spacial" pin:

"PA4 offers a reduced touch sensing sensitivity. It is thus recommended to use it as sampling capacitor I/O."

That is why it has this reset value in GPIOA_MODER register.

-Amel

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