關于一個單片機矩陣鍵盤掃描的代碼,為什么要賦0xfe給P1

ID:253022 · 發表于 2017-12-8 21:50

代碼里面標紅的那塊，有點疑問。不知道這段代碼的意思。為什么要賦0xfe給P1，不是要檢測P1的電位嗎？賦了0xfe給P1，還怎么檢測？

#include <reg52.h>
#include <intrins.h>
#define uchar unsigned char
#define uint unsigned int

uchar code DSY_CODE[]=
{
   0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e,0x00
};
uchar code KeyCodeTable[]=
{
   0x11,0x12,0x14,0x18,0x21,0x22,0x24,0x28,0x41,0x42,0x44,0x48,0x81,0x82,0x84,0x88
};

void Delay()
{
   uchar i;
for(i=0;i<200;i++);
}

uchar Keys_Scan()
{
   uchar sCode,kCode,i,k;
P1 = 0xf0;
if((P1&0xf0)!=0xf0)
{
      Delay();
      if((P1&0xf0)!=0xf0)
      {
           sCode = 0xfe;
         for(k=0;k<4;k++)
         {
               P1 = sCode;
            if((P1&0xf0)!=0xf0)
            {
                  kCode = ~P1;
                  for(i=0;i<16;i++)
                  {
                     if(kCode == KeyCodeTable[ i])
                        return i;
                  }
            }
            else
                  sCode = _crol_(sCode,1);
         }
      }
}
return -1;
}

void main()
{
   uchar KeyNO = -1;
uchar i,P2_LED,P3_LED;
while(1)
{
      KeyNO = Keys_Scan();
      if(KeyNO != -1)
      {
         P2_LED = 0xff;
         P3_LED = 0xff;
         for(i=0;i<=KeyNO;i++)
         {
               if(i<8)
                  P3_LED>>=1;
            else
                  P2_LED>>=1;
         }
         P3 = P3_LED;
         P2 = P2_LED;
      }
}
}