请教读按键程序.

只看该作者 · 2008-5-11 14:06

#include "keyScan.h"

#include <reg51.h>
#define KEY_BOARD P1
#define DELAY_VALUE 500
/*****************
延时子程序
*****************/
void delay()
{
unsigned short data i;
for(i = DELAY_VALUE;i != 0;i--);
}
/**********************
取得当前按键码
**********************/
unsigned char getKey()
{
unsigned char data keyState,scan,count,keyCode;
keyCode = 0xff;
/*是否有键按下*/
KEY_BOARD = 0xf0;
keyState = KEY_BOARD | 0x0f;
keyState = ~keyState;
if(!keyState) return keyCode;
delay();
KEY_BOARD = 0xf0;
keyState = KEY_BOARD | 0x0f;
keyState = ~keyState;
if(!keyState) return keyCode;
/*键盘扫描*/
scan = 0xfe;
for(count = 0;count < 4;count++){
     KEY_BOARD = scan;
     scan <<= 1;
     scan ++;
     keyState = KEY_BOARD & 0xf0;
     if(keyState){
          switch(keyState){
          case 0xe0:
               keyCode = count;
               break;
          case 0xd0:
               keyCode = count + 4;
               break;
          case 0xb0:
               keyCode = count + 8;
               break;
          case 0x70:
               keyCode = count + 12;
               break;
          }
     }
     if(keyCode != 0xff) break;
}
//等到按键松开
do{
    KEY_BOARD = 0xf0;
    keyState = KEY_BOARD | 0x0f;
    keyState = ~keyState;
}while(keyState);
return keyCode;
}

只看该作者 · 2008-5-11 14:10

keyState = KEY_BOARD | 0x0f;
keyState = ~keyState;
if(!keyState) return keyCode;

上面那三行不懂,不知道是做什么用的?
keyState 的值好像被覆盖了那么keyState = KEY_BOARD | 0x0f;这句好像没有意义了吧,?