hi, community, when gpioC is configured as input mode and default pin state is low.i am checking all pin by connecting each pin to ground alternatively.in that I find that pc8 and pc9 do not go high.

When a pin is configured as input, the default pin state is not low, but undefined. It might be low today and high tomorrow, or change every time you wave your hand in its general direction.

Check the GPIOC->MODER register to see if it is really set to input mode, never trust a library function to do it.

Check the board schematics, there might be some onboard peripherals connected to these pins, or bridges missing between the pin header and the MCI pin. Make sure you are looking at the right schematics, there are a couple of different boards based on that MCU.

Some pins can be destroyed with 5V, check the datasheet to see if they are 5V tolerant.

thank you for giving quick response and i will agree your point.

my code algorithm like this :

1)i am enable the port C by using RCC register

2) i am configuring the GPIOC->MODER register is zero because for input mode selection.

3) i am configuration these all port C pins as pull-up by using the GPIOC->PUPDR register.

4)now my observation is like:

1)All pins are high when pin is not shorted to ground including pc8 and pc9 pins.

2)All pins are low when pin is shorted to ground except these two pins i.e..,pc8 and pc9 pins.

here my doubt is why these two pins(pc8 and pc9 ) are not low when i am connected to ground when pin state configuration as pull-up.

is there any reason for these point?

>>currently i am using the stm32h743zi board

What board, specifically? Custom board, provide schematics.

On NUCLEO boards check solder bridge options, PC8/PC9 are SDIO/SDMMC as I recall. Check User Manual / Schematic