#include "stm32f4xx.h"
int main(void)
{ 
	uint32_t i;
	RCC->AHB1ENR|=RCC_AHB1ENR_GPIODEN;
	
	GPIOD->MODER = 0x55000000;
	GPIOD->OTYPER = 0;
	GPIOD->OSPEEDR = 0;
	
	while(1)
	{
		GPIOD->ODR = 0xf000;
		for(i=0;i<2000000;i++);
		GPIOD->ODR = 0x0000;
		for(i=0;i<2000000;i++);
	}
}