SysTick時鐘為HCKL的8分頻，故如果HCLK時鐘為72MHz，SysTick->LOAD的值為7200的話，則SysTick 1ms中斷
一次。如果屏蔽全局中斷的話，則STSTICK不能這用。

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例：
//SysTick 配置
if (SysTick_Config(SystemFrequency / 1000))// (72MHz/1000)*SYSCLK=1MS
{

while (1);
}
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//具體應(yīng)用
volatile u16 Timer1;
void SysTickDelay(u16 dly_ms)
{
Timer1=dly_ms;
while(Timer1);
}
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中斷函數(shù)

void SysTick_Handler(void)
{
if(Timer1)
Timer1--;
}