8条口线24按键的c51源程序 .c

单片机ＩＯ口不足

//8条口线24按键的C51源程序 
  
//海涛的笔记
  
//键盘扫描处理,无按键返回0,有按键返回键值,键值对应于keycode[]下标值。8条(以P2为例）口线24按键
//键盘码也可定义为局部数组变量
unsigned char code keycode[]=
{
	0x00,0xee,0xde,0xbe,0xed,0xdd,0xbd,0xeb,0xdb,0xbb,0xd7,0xe7,0xb7,0x7b,0x7d,0x7e,0x77,
	0xfe,0xfd,0xfb,0xf7,0xef,0xdf,0x7f,0xbf};

unsigned char keyread(void)
{ 
	unsigned char i,j,x,k1,k2;
	P2=0xff;
	if(P2!=0xff)
	{
		k1=P2;
		delay();
		P2=0xff;
		if(P2!=0xff)
		{
			for(P2=0xff;P2!=0xff;P2=0xff) x=k1;
		 }
	}
	else{x=0;}
//以上判断接地按键
//以下判断交叉按键(反转法）
	if(x==0)
	{
		P2=0x0f;
		if(P2!=0x0f)
		{
			delay();
			P2=0x0f;
			if(P2!=0x0f)
			{
				k1=P2;
				P2=0xf0;
				if(P2!=0xf0)
				{
					k2=P2;
					for(P2=0xf0;P2!=0xf0;P2=0xf0)
					x=k1^k2;
				}
			}
	}
	else{x=0;} 
	}
	if(x==0){i=0;}
	else{i=j=0xff;
	do
	{
		i++;
		j++;
		if(keycode[i]==x){j=24;}
		else if(j==24){i=0;}
		else{;} 
	}while(j!=24);}

	return(i);
}

void delay()//延时
{
	unsigned char b;
	for (b=0;b<=0xff;b++)
	{
		for (b=0;b<=0xff;b++)
		{;}
	}
}