About Pull-Up choice in STM32F4-DISCOVERY

[YAkse]

Hey, I have an STM32F4 discovery board which have a user button on it. I am setting button pin as input and when I try pull-down, it works as it should be,

HIGH when pressed

LOW when not pressed

But if I do not know wrong, when I choose pull-up then it should be

LOW when pressed

HIGH when not pressed

But this code below, gives me an always ON led , whether i am pressing or not.

 if(HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_0))

  HAL_GPIO_WritePin(GPIOD, LD4_Pin, 1);

else

HAL_GPIO_WritePin(GPIOD, LD4_Pin, 0);

Thanks in advance.

[oleksandr.karbivsky]

Hi. STM32F4-Discovery have a pull-down resistor (R39 220 KOhm) on board. Page 31 of user manual. Typical in-chip pull-up resistor is 40 KOhm. In this case voltage with unpressed button is 2.53 V (logic one).

[YAkse]

Hey, thanks for the answer. But I am also saying that it should be and it is HIGH with unpressed button. My problem is with pressed button case at pull-up configuration.

[oleksandr.karbivsky]

Pull-up configuration dont work with this board. Because when button pressed pin state is high. Check board schematic.

[YAkse]

If it is not working, then why is unpressed button resulting in a HIGH output ? ( When the button is configured as pull-up )

Also in CubeMX, why ST gives me opportunity to choose pull-up then ?

Thanks anyway.

[oleksandr.karbivsky · Accepted solution]

"If it is not working, then why is unpressed button resulting in a HIGH output ? ( When the button is configured as pull-up )"

Because the button is configured as pull-up (you answered on self question).

When button pressed it shorts with VCC. Check board schematic))

"Also in CubeMX, why ST gives me opportunity to choose pull-up then ?"

CubeMX give you opportunity to choose all functions, this don`t depend from board.

Special for you:

[YAkse]

Hey, thank you so much.

With your last eddition of that figure, now I understand it. At first I thought that R39 220K is the pull-down resistor. Which is not according to your figure.