4*4 keyboard function with buffered interrupt response

#include "scom.h"

unsigned char KeyNum[8]={0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff}; //Key value buffer
unsigned char KeyCntWr; //Write key value counter
unsigned char KeyCntRd; //Read key value counter
//unsigned char KeyNum;

void KeyInit(void)
{
    P1DIR=0Xf0;     
 P1REN=0X0f; //Enable pull-up
    P1OUT=0X0f;
 
    P1IFG=0x00;
    P1IE=0X0f; //Interrupt enable   
    P1IES=0X0f; //Column line falling edge allows P1 interrupt
}

void key_delay(Word _us)
{ 
  while(_us--);
}
//line number decoding
unsigned char coding(unsigned char n) //decoding
{
    switch(n)
    {
        case 0x0e: return 3; //input is 11111110 which is line number 3        
        case 0x0d: return 2; //input is 11111101 which is line number 2 
        case 0x0b: return 1; //input is 11111011 which is line number 1 
        case 0x07: return 0; //input is 11110111 which is line number 0 
  default : return 0xf0;
    }
}

//获取健值
unsigned char key(void)
{
    char temp,shift,keyname,a;
    temp=0x10;
    keyname=0xff;

    for(shift=0;shift<4;shift++)    
    {
        P1OUT=temp^0xff; //high four-bit output 11101111, 11011111, 101111111, 011111111, 11111111
        temp<<=1;
  a=P1IN&0x0f;
        if(a!=0x0f) //low four-bit input, if the port value is not detected to be high level, it means that a key is pressed in this column
            keyname=coding(a)+shift*4; //key value = row number + example number*4
    }
    return keyname; 
}

//Detect whether a key is pressed   
unsigned char keyj(void)      
{
    unsigned char x;
    x=(P1IN&0X0f); // P1.0--P1.3 are column lines, input, P1.4-P1.7 are row lines, output
    return(x); // No key is pressed, return 0x0f; a key is pressed, return non-0x0f
} 

//以查询方式获取键值，且译码。
unsigned char GetKey(void)
{   
    unsigned char key_value=0xff;
 
 if(KeyCntRd!=KeyCntWr)    //相等键盘缓存区无键值
 {
  switch(KeyNum[KeyCntRd])
  {
   case 0x00: key_value=0x0a;  break;  //dot
   case 0x01: key_value=0x06;  break;     //six
   case 0x02: key_value=0x07;  break;     //seven
   case 0x03: key_value=0x08;  break;     //eight
   case 0x04: key_value=0x09;  break;     //nine
   case 0x05: key_value=0x00;  break;     //zero
   case 0x06: key_value=0x0b;  break;     //Down
   case 0x07: key_value=0x0c;  break;     //Enter
   
   case 0x08: key_value=0x0d;  break;     //Esc
   case 0x09: key_value=0x01;  break;     //one
   case 0x0a: key_value=0x02;  break;     //two
   case 0x0b: key_value=0x03;  break;     //three
   case 0x0c: key_value=0x04;  break;     //four
   case 0x0d: key_value=0x05;  break;     //five
   case 0x0e: key_value=0x0e;  break;     //UP
   case 0x0f: key_value=0x0f;  break;     //Clear
   
   default  : key_value=0xff;  break;     
   
  }
  KeyCntRd++;
  if(KeyCntRd==8)
   KeyCntRd=0;
 }
 return(key_value);
}

#pragma vector=PORT1_VECTOR
__interrupt void Key_INT(void)
{
    if(keyj()!=0X0f)
    {
        key_delay(5000); //Debounceif
        (keyj()!=0X0f)
        {
     KeyNum[KeyCntWr++]=key();
   if(KeyCntWr==8) //If the keyboard buffer is full, start from the beginningKeyCntWr
      =0;
   
   if(KeyCntWr==KeyCntRd) //If the write counter is equal to the read counter, the read counter will increase by 1 accordingly 
   {
    KeyCntRd++;
    if(KeyCntRd==8)
     KeyCntRd=0;
   }
   BellOn(1);
  }
    }
    P1OUT=0X0f;
    P1IFG=0X00; //Clear interrupt flag
}

The cache key value is 7 or 8. That is, the last 7 or 8 key values ​​are valid.