►Programming AVR Microcontroller

►AVR Assembly Programming for 4x4 Keypad Matrix

.include "8515def.inc"

.equ col1 = PINA0
.equ col2 = PINA1
.equ col3 = PINA2
.equ col4 = PINA3

.def keyval = r16
.def temp = r17
.def flags = r18

.equ keyport = PORTA
.equ pressed = 0

key_init:
	ldi keyval,$F0		;Make Cols as i/p
	out DDRA, keyval	;and Rows as o/p
	ldi keyval,$0F		;Enable pullups
	out keyport, keyval	;on columns
	ret

get_key:
	ldi keyval,$0		;Scanning Row1
	ldi temp,$7F		;Make Row1 low
	out keyport,temp	;Send to keyport
	rcall read_col		;Read Columns

	sbrc flags,pressed	;If key pressed
	rjmp done		;Exit the routine

	ldi keyval,$4		;Scanning Row2
	ldi temp,$BF		;Make Row2 Low
	out keyport,temp	;Send to keyport
	rcall read_col		;Read Columns

	sbrc flags,pressed	;If key pressed
	rjmp done		;Exit from routine

	ldi keyval,$8		;Scanning Row3
	ldi temp,$DF		;Make Row3 Low
	out keyport,temp	;Send to keyport
	rcall read_col		;Read columns

	sbrc flags,pressed	;If key pressed
	rjmp done		;Exit the routine

	ldi keyval,$C		;Scanning Row4
	ldi temp,$EF		;Make Row4 Low
	out keyport,temp	;send to keyport
	rcall read_col		;Read columns

done:
	ret

read_col:
	cbr flags, (1<<pressed)	;Clear status flag

	sbic PINA, col1		;Check COL1
	rjmp nextcol		;Go to COL2 if not low

hold:
	sbis PINA, col1		;Wait for key release
	rjmp hold
	sbr flags, (1<<pressed)	;Set status flag
	ret			;key 1 pressed
nextcol:
	sbic PINA,col2		;Check COL2
	rjmp nextcol1		;Goto COL3 if not low

hold1:
	sbis PINA, col2		;Wait for key release
	rjmp hold1
	inc keyval		;Key 2 pressed
	sbr flags,(1<<pressed)	;Set status flag
	ret
nextcol1:
	sbic PINA,col3		;Check COL3
	rjmp nextcol2		;Goto COL4 if no pressed

hold2:
	sbis PINA, col3		;Wait for key release
	rjmp hold2
	inc keyval		;Key 3 pressed
	inc keyval
	sbr flags, (1<<pressed)	;Set status flag
	ret
nextcol2:
	sbic PINA,col4		;Check COL4
	rjmp exit		;Exit if not low

hold3:
	sbis PINA, col4		;Wait for key release
	rjmp hold3
	inc keyval		;Key 4 Pressed
	inc keyval
	inc keyval
	sbr flags, (1<<pressed)	;Set status flag
	ret
exit:
	clr keyval		;reset keyval
	cbr flags, (1<<pressed)	;No Key Pressed
	ret
	

►Programming AVR in C for 4x4 Keypad Matrix

#include <avr/io.h>
		// Include file for AVR
#define keyport PORTA		//Keypad Port
#define keyportddr DDRA		//Data Direction Register
#define keyportpin PINA		//Keypad Port Pins

#define col1 PA0		//Column1 PortA.0
#define col2 PA1		//Column2 PortA.1
#define col3 PA2		//Column3 PortA.2
#define col4 PA3		//Column4 PortA.3

#define TRUE 1
#define FALSE 0

unsigned char keyval;	//A variable

/*
+---------------------------------------+
| Prototype: void key_init(void);       |
| Return Type: void                     |
| Arguments: None                       |
| Description: Initialize ports and     |
|              Keypad.                  |
+---------------------------------------+
*/
void key_init(){
	keyportddr = 0xF0;
	keyport = 0x0F;
}

/*
+-----------------------------------------------+
| Prototype: unsigned char get_key(void);       |
| Return Type: unsigned char                    |
| Arguments: None                               |
| Description: To read key from the keypad      |
+-----------------------------------------------+
*/
unsigned char get_key(){
	unsigned char i,key=1;
	for(i=0;i<4;i++){		//Loop for 4 rows
		keyport &=~(0x80>
>
i);	//Make rows low one by one
			if(!(keyportpin & (1<<col1))){
			 //check COL1
				while(!(keyportpin & (1<<col1)));
				//wait for release
				return key;
				//return pressed key value
			}
			if(!(keyportpin & (1<<col2))){
			 //Check COL2
				key += 1;
				//Second key pressed
				while(!(keyportpin & (1<<col2)));
				//wait for release
				return key;
				//return key value
			}
			if(!(keyportpin & (1<<col3))){
			 //Check COL3
				key += 2;
				//Third key pressed
				while(!(keyportpin & (1<<col3)));
				//Wait for release
				return key;
				//Return value
			}
			if(!(keyportpin & (1<<col4))){
			 //check COL4
				key += 3;
				//Fourth key pressed
				while(!(keyportpin & (1<<col4)));
				//Wait for release
				return key;
				//Return key value
			}
		key +=4;	//Next row
		keyport |= 0x80>
>
i;
		//make read row high again
	}
	return FALSE;	//return false if no key pressed
}

Using these keypad routines is really simple.. here is a simple example that shows how to convert the key numbers to displayable ascii characters.

unsigned char translate(unsigned char keyval)
{
	if(keyval<10)
		return keyval+'0';
	else if(keyval>
=10 && keyval < 16)
		return keyval - 10 + 'A';
	else
		return '?';
}

/* usage */
ascii_key = translate(get_key());
/*
 * ascii_key will have the ascii equivalent of key pressed on the keypad
 * i.e. 0, 1, 2, 3, 4,...., A, B, C, D, E, F
 */

However the above function is just an example of how to use get_key function, you can define any translate function as per your requirement.


The next section of the tutorial will cover the programming of 8051. The usage example will apply to 8051 too.


◄ Connecting a Keypad  |  8051 Program ►