/* 
  4x4 Keypad Demo

  CodeVisionAVR C Compiler
  (C) 2000-2002 HP InfoTech S.R.L.
  www.hpinfotech.ro

  Chip: AT90S8515
  Connect the keypad matrix as follows:
   
  [STK500 PORTD HEADER]   [KEYS]  R1
  1 PD0 -----0----1----2----3----~~~~~---o+5V
             |    |    |    |     R2   |
  2 PD1 -----4----5----6----7----~~~~~-
             |    |    |    |     R3   |
  3 PD2 -----8----9----10---11---~~~~~-
             |    |    |    |     R4   |
  4 PD3 -----12---13---14---15---~~~~~-
         D1  |    |    |    |
  5 PD4 -|<|-     |    |    |
         D2       |    |    |
  6 PD5 -|<|------     |    |
         D3            |    |
  7 PD6 -|<|-----------     |  R1..R4=10k..47k
         D4                 |
  8 PD7 -|<|----------------   D1..D4=1N4148
   
  Use an 2x16 alphanumeric LCD connected
  to PORTC as follows:

  [LCD]   [STK500 PORTC HEADER]
   1 GND- 9  GND
   2 +5V- 10 VCC  
   3 VLC- LCD contrast control voltage 0..1V
   4 RS - 1  PC0
   5 RD - 2  PC1
   6 EN - 3  PC2
  11 D4 - 5  PC4
  12 D5 - 6  PC5
  13 D6 - 7  PC6
  14 D7 - 8  PC7
*/

#asm
    .equ __lcd_port=0x15
#endasm

#include <lcd.h>
#include <stdio.h>
#include <delay.h>
#include <90s8515.h>

// quartz crystal frequency [Hz]
#define F_XTAL 3686400L
// PIND0..3 will be row inputs
#define KEYIN PIND
// PORTD4..7 will be column outputs
#define KEYOUT PORTD
// used for TIMER0 count initialization
#define INIT_TIMER0 TCNT0=0x100L-F_XTAL/64L/500L
#define FIRST_COLUMN 0x80
#define LAST_COLUMN 0x10

typedef unsigned char byte;
// store here every key state as a bit,
// bit 0 will be KEY0, bit 1 KEY1,...
unsigned keys;
// LCD display buffer
char buf[33];

// TIMER 0 interrupt at every 2 ms
interrupt [TIM0_OVF] void timer0_int(void)
{
static byte key_pressed_counter=20;
static byte key_released_counter,column=FIRST_COLUMN;
static unsigned row_data,crt_key;
// reinitialize TIMER0
INIT_TIMER0;
row_data<<=4;
// get a group of 4 keys in in row_data
row_data|=~KEYIN&0xf;
column>>=1;
if (column==(LAST_COLUMN>>1))
   {
   column=FIRST_COLUMN;
   if (row_data==0) 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;
   };
// select next column, inputs will be with pull-up
KEYOUT=~column;
}

// test if a key was pressed
unsigned inkey(void)
{
unsigned k;
if (k=keys) keys=0;
return k;
}

void init_keypad(void)
{
DDRD=0xf0;
INIT_TIMER0;
TCCR0=3;
TIMSK=2;
#asm("sei")
}

main() {
unsigned k;
init_keypad();
lcd_init(16);
lcd_putsf("CVAVR Keypad");
// read keys and display key code
while (1)
      {
      lcd_gotoxy(0,1);
      if (k=inkey())
         {
         sprintf(buf,"Key code=%Xh",k);
         lcd_puts(buf);
         }
      else lcd_putsf("NO KEY        ");
      delay_ms(500);
      }
}