智能车制作

标题: 请问PIT的用法 [打印本页]

作者: jchen5471 时间: 2010-1-17 15:58
标题: 请问PIT的用法
/现象

B灯闪动,周期是INTVERAL*(0.01)ms,可用来记时.
//demo by whut_wj

#include <hidef.h>    /* common defines and macros */
#include <MC9S12XS128.h>    /* derivative information */
#pragma LINK_INFO DERIVATIVE "mc9s12xs128"

#define  INTVERAL 10000
void SetBusClock(void)
{
CLKSEL=0X00;    //disengage PLL to system
PLLCTL_PLLON=1; //turn on PLL
SYNR=2;
REFDV=1;       //pllclock=2*osc*(1+SYNR)/(1+REFDV)=48MHz;
_asm(nop);       //BUS CLOCK=24M
_asm(nop);
while(!(CRGFLG_LOCK==1)); //when pll is steady ,then use it;
CLKSEL_PLLSEL =1;       //engage PLL to system;
}

void Dly_ms(int ms) //24M时为1ms
{
int i,j;
for(i=0;i<ms;i++)
   for(j=0;j<0x7ff;j++);
}

void PitInit(void)
{

PITCFLMT_PITE=0;    //disable PIT
PITCE_PCE0=1;       //enable timer channel 0
PITMTLD0=240-1;       //time base  240 clock cycles ,it's 0.1M Hz
PITMUX=0X00;          // ch0 connected to micro timer 0
PITLD0=INTVERAL-1;    //INTVERAL micro time bases
PITINTE_PINTE0=1;    //enable interupt channel 0
PITCFLMT_PITE=1;    //enable PIT

                        //PITCNT0,类似于自由记数器,只不过一直是递减,TCNT是一直递增
}

void main(void)
{

EnableInterrupts;
SetBusClock();
PitInit();
DDRB=0xff;

for(;;)
{

}
}

#pragma CODE_SEG __NEAR_SEG NON_BANKED
void interrupt 66 PIT0Interrupt(void)
{
PORTB^=0xff;
   PITTF_PTF0=1;
}

该程序是定时1s，可是做出来后效果却不是为什么

作者: fi2005 时间: 2010-1-21 19:34
你的定时时间是0.1S

作者: jiangjie1229 时间: 2011-4-23 19:11
24M/240=0.1MHZ 0.1M/10000=10HZ 即0.1s

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