MCU pin not getting low even after enabling pull-down resistor for that specific pin

[GPach.3]

 I was implementing 2-way switch project on my Nucleo-F303RE. For that, I put the 13th and 14th pins of port-c as input and the 15th pin of the same port as output. I am using pull-down resistor for 13th and 14th pin but even after enabling pull-down resistor of these pins. SFR window in debug mode shows 13th bit of IDR still high.

 I have made sure that no pin should be connected to any external source

Here is my code and screenshots:

 /*

* Pin 13, 14, 15 of port-c will be used:-

  -> 13 and 14 pins will be used for input

  -> 15 pin will be used for output

* RCC address - 0x40021000 :-

  -> RCC_AHBENR - 0x40021014

  -> 19th bit for GPIOC

* GPIOC address - 0x48000800 :-

  -> GPIOC_MODER - 0x48000800

   => 15 (31[0] and 30[1]), 14(29[0] and 28[0]), 13(27[0] and 26[0])

  -> GPIOC_PUPDR - 0x48000808 :-

   => 14(29[1] and 28[0]), 13(27[1] and 26[0])

  -> GPIOC_IDR  - 0x48000810 :-

   => 13th and 14th bits

  -> GPIOC_ODR  - 0x48000814 :-

   => 15th bit

*/

#include<stdio.h>

#include<stdint.h>

int main(void)

{

uint32_t volatile *const pClkCntrl      = (uint32_t*)0x40021014;

uint32_t volatile *const pPortCMode   = (uint32_t*)0x48000800;

uint32_t volatile *const pPortCPullDwn = (uint32_t*)0x4800080C;

uint32_t volatile *const pPortC_IP     = (uint32_t*)0x48000810;

uint32_t volatile *const pPortC_OP    = (uint32_t*)0x48000814;

*pClkCntrl   |= ( 1 << 19 );    // enabling clock for GPIOC

*pPortCMode  &= ~(0xFC000000);    // reseting port c mode reg

*pPortCMode  |= (0x40000000);    // setting 15th(port-c) pin in output mode and 13th and 14th pins of port-c in input mode

*pPortCPullDwn &= ~(0x3C000000);    // resetting port c pull-up, pull-down reg

*pPortCPullDwn |= (0x28000000);    // enabling pull-down resistor for 13th and 14th pin

    /* Loop forever */

for(;;);

}

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[TDK · Accepted solution]

> Nucleo-F303RE

> 13th and 14th pins of port-c as input and the 15th pin of the same port as output

PC13-15 are not good choices since they're connected to things on the board.

 

Schematic is available on the resources page:

https://www.st.com/en/evaluation-tools/nucleo-f303re.html#documentation

You can remove these components but you'll also need to make sure PC13MODE, PC14MODE and PC15MODE are configured to allow these to work as standard GPIO pins.

[GPach.3]

thanks, by choosing different pins it worked