51單片機跑馬燈問題，端口直接賦值和變量賦值的區別

ID:308903 · 發表于 2018-8-24 16:17

先總結說明下：

第一個程序，來著開發板自帶程序，可以正常左右循環；第二個程序只是取消了 uchar LED 這個變量，直接賦值P2 端口，就不行了!

不知道為什么? 求指點下，是不是哪個概念沒理解清楚？

這個程序是正常運行的，來著普中開發板

#include <reg52.h>
void delay(unsigned int i);
char LED;

main()
{
  unsigned char i;

  while (1)
  {       LED = 0xfe;

         for (i = 0 ;i < 8 ; i++)
      {
         P2  = LED;
         delay(500);
         LED = LED << 1;
         LED = LED | 0x01;
         if (LED == 0x7f)       break;
         }

         for (i = 0 ;i < 8 ; i++)
         {

               P2  = LED;
               delay(500);
               LED = LED >> 1;
               LED = LED | 0x80;

         }

}

}

/******延時*************/
void delay(unsigned int i)
{
unsigned char j;
for(i; i > 0; i--)
      for(j = 255; j > 0; j--);

}

下面這個程序，就只能跑一下了！#include  < reg52.h >

#define uchar unsigned  char
#define uint  unsigned  int

/*****延時*****/

void delayMS  ( uint  ms )
{
  uchar i;

  while ( ms-- )
  {
for ( i = 0;  i < 255;  i++ );
  }
}

/***主函數***/

void  main  ()
{
  uchar i;

  while ( 1 )
  {

for ( i = 0;  i < 8;  i++ )
   {
   P2  = 0xfe;
   delayMS ( 500 );

   P2 = P2  << 1;
   P2 = P2  | 0x01;

   if ( P2  == 0x7f )
   break;
   }

   for  ( i = 0;  i < 8;  i++ )
   {
   P2 = 0xfe;
   delayMS  ( 500 );

   P2 = P2  >> 1;
   P2 = P2  | 0x80;
   }
  }
}