矩陣鍵盤掃描方式：

第一種：逐行掃描法，就是一行一行的掃描。實(shí)現(xiàn)代碼如下(鍵盤連接P2口)：

#define NO_KEY 0XFF

#define KEY_LO() P2 &= 0XF0

#define KEY_HI() P2 |= 0X0F

#define KEY_L(i) P2 &= ~(1<

#define KEY_RD() ((P2>>4) & 0x0f)

UINT8 OnceKey(void)

{

UINT8 line = 0;

UINT8 key = NO_KEY;//key value

KEY_LO();

if (KEY_RD() == 0X0F)

{

KEY_HI();

return NO_KEY;

}

for (line=0; line<4; line ++)

{

KEY_HI();

KEY_L(line);

key = KEY_RD();

switch (key)

{

case ROW_FIRST:

key = 4*line + 0;

break;

case ROW_SECOND:

key = 4*line + 1;

break;

case ROW_THIRD:

key = 4*line + 2;

break;

case ROW_FOURTH:

key = 4*line +3;

break;

default :

key = 0x0f;

break;

}

if (key < 0x10)

{

return key;

}

}

return NO_KEY;

}

第二種，線性反轉(zhuǎn)法。就是行和列分別讀出。實(shí)現(xiàn)代碼如下：

#define CVT(i) ((i)==(~1)&0x0f)? 0: ((i)==(~2)&0x0f)? 1: ((i)==(~4)&0x0f)? 2: ((i)==(~8)&0x0f)? 3: 4;

#define KEY0_3HI() P2 |= 0X0F

#define KEY0_3LO() P2 &= 0XF0

#define KEY4_7HI() P2 |= 0XF0

#define KEY4_7LO() P2 &= 0X0F

#define KEY0_3RD() (P2 & 0X0F)

#define KEY4_7RF() ((P2>>4) & 0X0F)

UINT8 OnceKey(void)

{

UINT8 line = NO_KEY;

UINT8 row = NO_KEY;

UINT8 key;

KEY0_3HI();

KEY4_7LO();

line = KEY0_3RD();//讀入行的值

if (0x0f == line)

{

key = NO_KEY;

}

else

{

KEY0_3LO();

KEY4_7HI();

row = KEY4_7RD();//讀入列的值

if (0x0f == row)

{

key = NO_KEY;

}

else

{

key = CVT(line)*4 + CVT(row);

}

}

KEY0_3HI();

KEY4_7HI();

return key;

}