PS/2 Keyboard Interface C51 Driver

/**************************
 Resources used by the file
1. External interrupt 0
2. Port: P3.3, P3.4
**************************/
sbit PS2_DAT=P3^7; //Data

uchar code unshifted[][2]= //shift key not pressed decoding table
{  
  0x0e,'`',
  0x15,'q',
  0x16,'1',
  0x1a,'z',
  0x1b,'s',
  0x1c,'a',
  0x1d,'w',
  0x1e,'2',
  0x21,'c',
  0x22,'x',
  0x23,'d',
  0x24,'e',
  0x25,'4',
  0x26,'3',
  0x29,' ',
  0x2a,'v',
  0x2b,'f',
  0x2c,'t',
  0x2d,'r',
  0x2e,'5',
  0x31,'n',
  0x32,'b',
  0x33,'h',
  0x34,'g',
  0x35,'y',
  0x36,'6',
  0x39,',',
  0x3a,'m',
  0x3b,'j',
  0x3c,'u',
  0x3d,'7',
  0x3e,'8',
  0x41,',',
  0x42,'k',
  0x 43,'i',
  0x44,'o',
  0x45,'0',
  0x46,'9',
  0x49,'.',
  0x4a,'/',
  0x4b,'l',
  0x4c,';',
  0x4d,'p',
  0x4e,'-',
  0x52,'\'',
  0x54,'[',
  ', 0x7a,'3 '
  ,
  0x7b
  ,'
  -',
  0x7c,'*',   0x7d,'9', 0,0 }; uchar code shifted[   ]
  [   2
  ] = //shift key pressed decoding table   { 0x0e   ,'~',   0x15   ,   'Q',   0x16 ,   ' !   '   ,   0x1a,'Z   '   ,   0x1b,'S',   0x1c,'A',   0x1d,'W',   0x1e,'@',   0x21,'C',   0x22,'X',   0x23,'D',   0x24,'E',   0x25,'$',   0x26,'#',   0x29,' ',   0x2a,'V',   0x2 b,'F',   0x2c,'T',   0x2d,'R',   0x2e,'%',   0x31,'N',   0x32,'B',   0x33,'H',   0x34,'G',   0x35,'Y',   0x36,'^',   0x39,'L',  0x3a,'M',   0x3b,'J',   0x3c,'U',   0x3d,'&',   0x3e,'*',   0x41,'<',   0x42,'K',   0x43,'I',   0x44, 'O',   0x45,')',   0x46,'(',   0x49,'>',   0x4a,'?',   0x4b,'L',   0x4c,':',   0x4d,'P',   0x4e,'_ ',   0x52,'"',   0x54,'{',   0x55,'+',   0x5b,'}',   0x5d,'|',   0x61,'>',   0x69,'1',   0x6b,'4',   0x6c,'7',



































































  0x70,'0',
  0x71,'.',
  0x72,'2',
  0x73,'5',
  0x74,'6',
  0x75,'8',
  0x79,'+',
  0x7a,'3',
  0x7b, '-',
  0x7c,'*',
  0x7d,'9',
  0,0
};

void Decode(uchar scancode);//declare function prototype
uchar bitcount,bytecount,byte2; //edge is 0 falling edge interrupt, 1 rising edge interrupt
uchar ascii2[35],ascii[99]; //bitcount is the bit count value
         //ascii is the translated ASCII code, the initial value is space
//******************************************************         
//External interrupt service subfunction  
//*******************************************************       
void StopInt() interrupt 0 
{   
 static uchar udata; //Declare local static variables to save scan codes
   if(bitcount < 11 && bitcount > 2) //3 to 10 bits are data, start bit, check bit and stop bit are ignored
   { 
    udata = (udata >> 1); //right shift to save data
  if(PS2_DAT)
  {
     udata|=0x80; //store a '1'
  }
   }
    if(--bitcount==0) //If all 11 bits are received
   {
     bitcount = 11; //Reset to 11-bit data
  ascii[bytecount]=udata;
  if(bytecount<6)bytecount++;
   }
}   
/*******************************************
Function name: DecodeFunction
: 
Parameter: scancode--scan code to be translatedReturn
value: None
/********************************************/
void Decode(uchar scancode)
{
  static uchar up=0,shift=0; //up is the pass/break code flag, shift is the shift key pressed flaguchar
  i;
  if (!up) //The received 11-bit data is a pass code (up is 0)
  {
    switch (scancode)//Start translating the scan code
    {
     case 0xF0: //Keyboard release flag (the following byte is a break code)
      up=1; //Set up to the break code flagbreak
      ;
      case 0x12: //Left shift key pressedshift
      =1; //Set shift to the pressed flagbreak
      ;
      case 0x59: //Right shift key pressedshift
      =1; //Set shift to the pressed flagbreak
      ;   
      default:        
      if(!shift) //If the shift key is not pressed
   { //Look up the unshifted table, the left column in the table is the scan code, and the right column is the corresponding ASCII code
        for(i=0;unshifted[i][0]!=scancode&&unshifted[i][0];i++);
         if(unshifted[i][0]==scancode) 
         {
           ascii2[3]=unshifted[i][1];
         }
   } 
   else //If the shift key is pressed
   { //Look up the shifted table
      for(i=0;shifted[i][0]!=scancode&&shifted[i][0];i++);
         if(shifted[i][0]==scancode) 
         {
           ascii2[3]=shifted[i][1];
         }
   }   
      break;
    }
  } 
  else //The received 11-bit data is a broken code (up is 1)
  {
    up = 0; //Reset the broken code flag
    switch (scancode) //Detect shift key release
    {
      case 0x12 : //Left shift key
      shift = 0;
      break;
      case 0x59: //right shift key
      shift = 0;
      break;
      default:
      break;
    }
  }
}