矩阵键盘只有一个按键有反应问题

按下按键四有反应，按下五和九没反应，是没跳出去case 4吗
void key_proc(void)
{
unsigned char keyold, keydown, Key_Val;
if(keytime) return ;
keytime=1;
Key_Val = key_read();
keydown = Key_Val & (Key_Val ^ keyold);
keyold = Key_Val;
switch (keydown)
{
case 4:
dianya ^= 1;
break;
case 5: {
P0 = 0XFF;
P2 = (P2 & 0X1F) | 0XE0;
P2 = 0X1F;
} break;
case 9: {
led^=1;
if(led==1)
{
led_proc();
led=0;
}
else{ P2 = 0XFF;
P2 = (P2 & 0X1F) | 0X80;
P2 = 0X1F;
led = 0;
}
} break;
}
}