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pic16f877a- keypad not working

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navintiwari08

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hello everyone..
I'm trying to interface a 4x4 matrix keypad to 16f877a.. the following code written in hi tech c is not working.. the program is printing characters of the array randomly without a keypress.. please help.. i'm using mplab 8.85.. using lcd 16x2..
NOTE: if I change the value of TRISC to 0x00, the code works fine.. but then i'm not making any input ports.. so how is it scanning a key press..?
thanks in advance..
Code: 
#include<htc.h>
#define _XTAL_FREQ 20000000
#define lcd PORTB
#define key PORTC
#define rs RE0
#define rw RE1
#define en RE2

__CONFIG(FOSC_HS&LVP_OFF&BOREN_OFF&CP_OFF&PWRTE_OFF&WRT_OFF&WDTE_OFF);

void lcd_init();
void lcd_cmd(unsigned char);
void lcd_data(unsigned char);

void main()
{
        unsigned char col,row;
        unsigned char i[4][4]={'0','1','2','3',
                                                   '4','5','6','7',
                                           '8','9','A','B',
                                                   'C','D','E','F'};
        TRISB=0x00;
        TRISE=0X00;
        __delay_ms(2);
        ADCON1=0x07;
        lcd_init();
        while(1)
        {
                do
                {
                        TRISC=0x0f;
                        key=0x0f;
                        col=key;
                        col=col&0x0f;
                }
                while(col!=0x0f);
               
                do
                {      
                        do
                        {
                                __delay_ms(5);
                                col=key;
                                col&=0x0f;
                        }
                        while(col==0x0f);
                        __delay_ms(10);
                        col=key;
                        col&=0x0f;
                }
                while(col==0x0f);
                       
                while(1)
                {
                        key=0x7f;
                        col=key;
                        col&=0x0f;
                        if(col!=0x0f)
                        {
                                row=3;
                                break;
                        }
                       
                        key=0xbf;
                        col=key;
                        col&=0x0f;
                        if(col!=0x0f)
                        {
                                row=2;
                                break;
                        }

                        key=0xdf;
                        col=key;
                        col&=0x0f;
                        if(col!=0x0f)
                        {
                                row=1;
                                break;
                        }

                        key=0xef;
                        col=key;
                        col&=0x0f;
                        if(col!=0x0f)
                        {
                                row=0;
                                break;
                        }
               
                }
                if(col==0x0e)
                        lcd_data(i[row][0]);
                else if(col==0x0d)
                        lcd_data(i[row][1]);
                else if(col==0x0b)
                        lcd_data(i[row][2]);
                else if(col==0x07)
                        lcd_data(i[row][3]);
        }
}

void lcd_init()
{
        unsigned char cmd[]={0x38,0x0e,0x01,0x06,0x80};
        unsigned char i;
        for(i=0;i<=4;i++)
        {
                lcd_cmd(cmd[i]);
                __delay_ms(10);
        }
}

void lcd_cmd(unsigned char x)
{
        rs=0;
        rw=0;
        lcd=x;
        en=1;
        __delay_us(2);
        en=0;
}

void lcd_data(unsigned char x)
{
        rs=1;
        rw=0;
        lcd=x;
        en=1;
        __delay_us(2);
        en=0;
}
 

if not using, make use of the pull up and pull down resistors so that the ports would keep at constant default values.
 

this's code I used to scan keypad 4x4

Code: 
#define KEY		PORTC

#define col_0	RC4
#define col_1	RC5
#define col_2	RC6
#define col_3	RC7


	char key_tab[4][4]={ '1', '2', '3', 'A',
				     '4', '5', '6', 'B',
				     '7', '8', '9', 'C',
				     '*', '0', '#', 'D'};
						 
	char scan_row[4]={0b00001110,0b00001101,0b00001011,0b00000111};

TRISC=0xf0;
//-------------------------------------------------------//
// READ KEYPAD 4x4 FUNCTION				       //
//-------------------------------------------------------//
char scan_key()
{
	char row=0;
	
	for(row=0;row<4;row++)
	{
		KEY=scan_row[row];
		
		if(col_0==0){while(col_0==0);return key_tab[row][0];};
		if(col_1==0){while(col_1==0);return key_tab[row][1];};
		if(col_2==0){while(col_2==0);return key_tab[row][2];};
		if(col_3==0){while(col_3==0);return key_tab[row][3];};
	}
	return '\0';
}
 

I am talking about the hardware !
Rows if you are taking them as input add up a pullup resistor so that the defualt stays 1 and coloumns as output add up pull down resistor so that the defualt value is at 0.
Normally there is no constant current flow, it varies up +/- 1.5v ac, and when u r stepping down there will lot of flucations and keypad doesnt recoginse properly.
 

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