初学AVR，请教大湿一个数码管动态显示器设计的问题

只看该作者 · 2013-10-31 20:01

问题1：time_counter为什么要自加到40，在晶振为4MHZ时自加一次时间怎样算啊？
问题2：在void display(void)函数里最后为什么要PORTC =0xff关闭所有数码管，直接更新数据不行吗，我删除后的确不行，是什么原因
#include <mega16.h>
#include <delay.h>
char time[3];
char dis_buff[6];
flash char led_7[10]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,0x7F,0x6F};
bit point_on;
flash char position[6]={0xfe,0xfd,0xfb,0xf7,0xef,0xdf};
char time_counter;

void time_to_disbuffer(void)
{
  char i,j=0;
  for(i=0;i<2;i++)
  {
dis_buff[j++] = time % 10;
dis_buff[j++] = time / 10;
  }
}

void display(void)
{
  char i;
  for(i=0;i<=5;i++)
  {
PORTA = led_7[dis_buff];
if (point_on && (i==2||i==4)) PORTA |= 0x80;
PORTC = position;
delay_ms(2);
PORTC =0xff;
  }
}

void main()
{
  PORTA=0x00;    //初始化POTA
  DDRA=0xFF;
  PORTC=0x3F;    //0011 1111
  DDRC=0x3F;    //0011 1111,PORT0-PORT5输入

  time[2] = 23;
  time[1] = 58;
  time[0] = 55;

  time_to_disbuffer();

  while(1)
  {
display();
if(++time_counter >=40)
{
   time_counter = 0;
   point_on=~point_on;
   if(++time[0]>=60)
   {
      time[0] = 0;
      if(++time[1]>=60)
      {
      time[1] = 0;
      if(++time[2]>=24) time[2] = 0;
      }
      time_to_disbuffer();
   }
   delay_ms(13);
}
  }
}