keypad.c

this is keypad driver for 4x4 matrix keypad for ATMEGA32 Microcontroller from Atmel

#include <mega32.h>
#include "keypad.h"
#include "cryptophone.h"

/***************************************************************************************************
  Location : PORTC
  Config   : 11110000
             High nibble is used to select row and low column is to read the whole row.
***************************************************************************************************/
// Lookup Table
unsigned int keys = 0;
flash unsigned char key_table[17]={ 0,
                                    'D','#','0','*',
                                    'C','9','8','7',
                                    'B','6','5','4',
                                    'A','3','2','1' };                                  



/***************************************************************************************************
  Function Name        : interrupt [TIM2_OVF] void timer2_int(void) 
  Description          : Scheduled keypad scanning process based on timer2 overflow interrupt which
                         is occured every 2ms;
  Number of Argument   : none
  Type of Argument     : void
  Type of Return Value : void
***************************************************************************************************/

interrupt [TIM2_OVF] void timer2_int(void){
    static unsigned char key_pressed_counter=20;
    static unsigned char key_released_counter,column=FIRST_COLUMN;
    static unsigned int  row_data,crt_key;
      
    TCNT2 = KEYPAD_TIMER_SET;               // initialize timer2
    row_data <<= 4;  
    row_data |=  (~KEYIN & 0x0f);
    column   >>= 1;
    if (column == (LAST_COLUMN>>1)){
        column = FIRST_COLUMN;
        if (!row_data) goto new_key;
        if (key_released_counter){
            --key_released_counter;
        }else{
            if (--key_pressed_counter == 9){
                crt_key=row_data;
            }else{
                if (row_data != crt_key){
new_key:            key_pressed_counter = 10;
                    key_released_counter = 0;
                    goto end_key;
                };
            if (!key_pressed_counter){
                keys = row_data;
                key_released_counter = 20;
            };
         };
      };
end_key:;
   row_data = 0;
   };
KEYOUT = ~column;
}



    
/***************************************************************************************************
  Function Name        : unsigned char inkey(void)
  Description          : Convert scanned data provided by scanning routine.
                         The scanning routine provides scanned key as a 16 bit string, while the
                         pressed key is simply represented by the location of non zero bit.
  Assumption           : the [keys] variable contains scanned key
  Number of Argument   : none
  Type of Argument     : void
  Type of Return Value : ASCII character [0123456789*#ABCD]
***************************************************************************************************/
unsigned char keypad_read(void){
    unsigned char i=0;          // declare bit counter
    while(keys){                // detect non zero bit location and save it to i
        keys >>= 1;
        i++;
    }
    return key_table[i];
}




/***************************************************************************************************
  Function Name        : void init_keypad(void)
  Description          : Initialize Keypad 
  Assumption           :   
  Number of Argument   : 
  Type of Argument     : 
  Type of Return Value : 
***************************************************************************************************/
void keypad_init(void){
    TCNT2 = KEYPAD_TIMER_SET;                                       // set to overflow every 2ms
    TCCR2 = ( TIMER_COUNTER_2_NORMAL_PORT_OPERATION |               // Use OC2 as normal
              TIMER_COUNTER_2_CLOCK_SELECT_CLK_IO_PRESCALING_256 |  // prescalar 256
              TIMER_COUNTER_2_WAVEFORM_NORMAL );                    // Use timer2 as norml mode
    TIMSK = TIMER_COUNTER_2_OVERFLOW_INTERRUPT_ENABLE;              // enable timer2 overflow
}