Posted on June 30, 2014 at 22:08Hi.
I use a STM32F103ZE microcontroller.
I try to change the System Clock (default is HSI) to HSE.
On my board is a HSE - cristal oscilator which value is 8 Mhz and i want to change it to 72 Mhz and it works.
But if i want to change it to a small value , for instance 24 Mhz i cannot change it, even if i made the setup (RCC->CFGR |= (1 << 16) | (1 << 18); ).
One more quetion : how many clock cycles takes to execute an instruction ?
#include<stm32f10x.h>
void wait(void)
{
int d;
for(d = 0; d < 1000000; d++);
}
int main (void)
{
unsigned int i;
RCC->CR &= ~(1 << 0);
RCC->CR |= (1 << 19);
RCC->CR &= ~(1 << 16);
RCC->CR &= ~(1 << 24);
RCC->CFGR &= ~(1 << 17);
RCC->CFGR |= (1 << 0);
RCC->CFGR &= ~(1 << 1);
RCC->CFGR |= (1 << 16) | (1 << 18) | (1 << 19) | (1 << 20);
RCC->CFGR |= (1 << 25) | (1 << 26);
RCC->CR |= (1 << 24);
RCC->CR |= (1 << 16);
RCC->APB2ENR |= (1UL << 7); // Enable GPIOF
GPIOF->CRL = 0x33000000; // PF.6, PF.7 defined as Outputs
GPIOF->CRH = 0x33; // PF.8, PF.9 defined as Outputs
while (1)
{
for(i = 1<<6; i < 1<<10; i <<= 1)
{
GPIOF->BSRR = i; // Turn LED on
wait();
GPIOF->BRR = i; // Turn LED of
}
}
}
