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cembeddedstm32stm32cubeide

STM32 Button Read

What is the difference between MODER's input mode and PUPDR. I saw some code parts for buttons. One code is like

GPIOB->MODER &= ~(3U << 2*4); // PB4
GPIOB->MODER |= (0U << 2*4);

and another code is,

GPIOB->MODER &= ~(3U << 2*8);  //PB8
GPIOB->PUPDR |= (2U << 2*8);

should I make MODER register as an input like first one? But second one is just clearing MODER register and making PUPDR as Pull-up.

shouldn't I making MODER as input first?

Solution

  • To read a button on STM32, you should adjust the MODER as input. Then, you can just check the IDR(Input Data Register).

    For PUPDR, you need this register if you do not have any externally connected Pull-up or pull-down resistor.

    The second code assigns the specific port as input with pull-down configuration, in your example. So it is your decision to make it either pull-down or pull-up.

    The first code is doing the same thing twice on the both lines.