Interface matrix Keypad

March 25, 2013 Coded in C for the Microchip PIC16

This is a driver for interfacing 4x4 matrix keypad with PIC microcontroller

/Keypad connection: 

#define col0 PIN_B3
#define col1 PIN_B2
#define col2 PIN_B1
#define col3 PIN_B0
#define row0 PIN_B7
#define row1 PIN_B6
#define row2 PIN_B5
#define row3 PIN_B4

#define num_col 4

// Keypad layout:
char const KEYS[4][4] = {{1,2,3,13},
                         {4,5,6,14},
                         {7,8,9,15},
                         {11,10,12,16}};

void init_keypad()
{
	output_high(row0);
	output_high(row1);
	output_high(row2);
	output_high(row3);
	output_low(col0);
	output_low(col1);
	output_low(col2);
	output_low(col3);	
}

short int ALL_ROWS (void)
{
   if (input (row0) & input (row1) & input (row2) & input (row3))
      return (0);
   else
      return (1);
}

//Will return a key value if pressed or 0 if not 

int8 get_key()
{
int8 row,col=0;
	do	
	{
		switch (col)
		{
			case 0   :
				output_low(col0);
				output_high(col1);
				output_high(col2);
				output_high(col3);
				break;
			case 1   :
				output_high(col0);
				output_low(col1);
				output_high(col2);
				output_high(col3);
				break;
			case 2   : 
				output_high(col0);
				output_high(col1);
				output_low(col2);
				output_high(col3);
				break;
			case 3   : 
				output_high(col0);
				output_high(col1);
				output_high(col2);
				output_low(col3);
				break;                    
		}
		
		if(!input (row0))
			row=1;
		else if(!input (row1))
			row=2;
		else if(!input (row2))
			row=3;
		else if(!input (row3))
			row=4;
		else
			row=0;
		col++;
	}while(!row && col<num_col);	
	if(row)
        return KEYS[row-1][col-1];
    else
        return 0;		
}
//function waits until any key is pressed and released.
int8 get_key_released()
{
int8 _key_temp ;
    do
    {
        _key_temp=get_key();
    }while(!_key_temp);
    init_keypad();
    do
    {
        while(ALL_ROWS());
        delay_ms(50);
    }
    while(ALL_ROWS());
return _key_temp;
}

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