[PIC] unexpected problem about resetting pic 16f877a

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MUKESH.K.S

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I am here with an very unexpected problem with 16f877a . In my circuit i used ports d,a& e as output port and ports d &c as output port. I have an 16*2 lcd display in my circuit. When i power the circuit the display works finely ie, it displays what i want. But the problem is pic doesn't senses any key press.
i used 10k and .1uf for the reset circuit . Then i removed the capacitor from the reset circuit and manually resetted the uc by connecting mclr to ground. After repeating this steps many times ,the uc starts reading the key press. It woks fine only after i manually resetting the uc several times .
What is the problem ? Please help me ....my code for setting the ports & circuit is given below


ADCON1=0X0F;
TRISD=0X00;
TRISA=0X00;
TRISB=0XFF;
TRISC=0XfF;
TRISE=0X00;
PORTE=0X02;
 

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There is some difference in 877 and 877A. You mention that you are using 877A chip but your circuit shows 877 chip. Confirm the chip. Your Keypad circuit is wrong. Google for 4X4 or 4X3 Keypad. If you are using 4X3 or 3X4 (12 Keys keypad) then you need only one PORT for the keypad interface (using digital IO). If you use ADC for keypad then you need only one ADC pin to interface Keypad.

Zip and post the Proteus file.


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//ADCON1 = 0x8E;    //using ADC AN0 for Keypad
//TRISA = 0x01;
ADCON1 = 0X87;  //Using digital IO for Keypad (PORTB)
TRISA = 0x00;
PORTA = 0x00;
TRISB = 0xFF;
PORTB = 0x00;
TRISC = 0x0F;
PORTC = 0x00;
TRISD = 0x00;
PORTD = 0x00;
TRISE = 0x00;
PORTE = 0x00;
 

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Hi,

As Milan says there are more efficient ways to use a keypad.


Assume the design is one you have found some where ? - its just using one port pin for each key so providing the program code is correct there is no reason it should not work.

Like the LCD its using 11 ports to control it, whereas with some more efficient code you can use just 7.

Would be better if you posted the whole program code so we can see what happening

Are you building on a breadboard ?
 

Two more things. If WDT is enabled then it wil be the reason for MCU resetting.

One

wp100 is right. You switch(s) connections are right. I didn't check the switch(s) circuits carefully. You are using just a simple button circuit which keeps the port pin 1 all the time and goes 0 on key press. A better way is to use 4X3 keypad circuit using digital IO or ADC which will simplify your switch(s) input circuit and its related code.

Two

RE0 is driving an LED and Transistor. remove the LED circuit and connect LED across relay coil.
 
Last edited:

Hi,

Also ADCON1 should be 0x06, 0x0F means RA2 becomes '-VREF' that might make your lcd incorrect.
 
wp100 is right again. I had made a typo (0x86 ----> 0x87). I had calculated these values for ADCON1 to use PORTA as digital IO

0x0F
0x06
0x8F
0x86

and

0x8E or 0x0E if AN0 is used for ADC keypad.
 
Thanks in advance for the reply..... here is my whole project folder . my project is password lock
( password is 4104)

- - - Updated - - -

Thanks for the replies. I changed ADCON1 reg value as you mentioned, but the problem still there. The micro controller works fine after resetting it several times manually. I am also thinking about the matrix keyboard. But my doubt is that why i cant use all the ports of uc?
 

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One problem I see is in KEY() function's switch() { } statement, break; is missing for all cases. Finding more bugs...

Edit:

Use this code to display LCD test

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void LCD_STRING(volatile unsigned char *temp1)
{
    while(*temp1)LCD_DATA(*temp1++);
}
 
LCD_STRING("LOCKED");


You should use something like this to check which key is pressed according to your key(s) circuit. Add debounce delay.

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if(!(PORTC & 0x03)) {
 
    if(PORTB = 0x01) {
 
    }
    else if(PORTB = 0x01) {
 
    }
    else if(PORTB = 0x02) {
 
    }
    else if(PORTB = 0x04) {
 
    }
    else if(PORTB = 0x08) {
 
    }
    else if(PORTB = 0x10) {
 
    }
    else if(PORTB = 0x20) {
 
    }
    else if(PORTB = 0x40) {
 
    }
    else if(PORTB = 0x80) {
 
    }
 
}
else if(!PORTB) {
    if((PORTC & 0x03) == 0x01) {
 
    }
    else if((PORTC & 0x03) == 0x02) {
 
    }   
}
 
Last edited:
Explain how your system has to work. The code can be written in a better way.

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#include <htc.h>
 
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 20000000
#endif
 
__CONFIG(FOSC_HS & WDTE_OFF & PWRTE_ON & BOREN_OFF &
LVP_OFF & WRT_OFF & DEBUG_OFF & CPD_OFF & CP_OFF);
 
#define LEN_PASSWORD 4
 
char NUMBER[LEN_PASSWORD];
unsigned int PRESS = 0, i = 0;
bit KEYSTAT = 0, LOCK = 0;
 
void LCD_COMMAND(char cmd);
void LCD_DATA(char dat);
void LCD_STRING(char *str);
void KEY(char);
char ASCII(char);
void INITIAL(void);
void SETKEYSTAT();
 
void SETKEYSTAT() {
        KEYSTAT = 1;
}
 
void main(void)
{
    ADCON1 = 0X0F;
    CMCON = 0x07;
    CVRCON = 0x00;
    
    TRISA = 0x00;
    TRISB = 0xFF;
    TRISC = 0x0F;
    TRISD = 0x00;
    TRISE = 0x00;
 
    PORTE = 0x02;
 
    LCD_COMMAND(0X38);
    LCD_COMMAND(0X0C);
    LCD_COMMAND(0X01);
    INITIAL();
 
    while(1)
    {
 
        if(!(PORTC & 0x03)) {
            __delay_ms(50);
        
            switch(PORTB) {
                case(0x01): {
                        while(PORTB == 0x01);
                        PRESS++;
                        KEY(0X01);
                        SETKEYSTAT();
                        break;
                }
                case(0x02): {
                        while(PORTB == 0x02);
                        PRESS++;
                        KEY(0X02);
                        SETKEYSTAT();
                        break;
                }
                case(0x04): {
                        while(PORTB == 0x04);
                        PRESS++;
                        KEY(0X03);
                        SETKEYSTAT();
                        break;      
                }
                case(0x08): {
                        while(PORTB == 0x08);
                        PRESS++;
                        KEY(0X04);
                        SETKEYSTAT();
                        break;      
                }
                case(0x10): {
                        while(PORTB == 0x10);
                        PRESS++;
                        KEY(0X05);
                        SETKEYSTAT();
                        break;      
                }
                case(0x20): {
                        while(PORTB == 0x20);
                        PRESS++;
                        KEY(0X06);
                        SETKEYSTAT();
                        break;      
                }
                case(0x40): {
                        while(PORTB == 0x40);
                        PRESS++;
                        KEY(0X07);
                        SETKEYSTAT();
                        break;      
                }
                case(0x80): {
                        while(PORTB == 0x80);
                        PRESS++;
                        KEY(0X08);
                        SETKEYSTAT();
                        break;      
                }               
            };
        
        }
        else if(!PORTB) {
            __delay_ms(50);
        
            switch(PORTC & 0x03) {
                case(0x01): {
                        while(PORTB == 0x01);
                        PRESS++;
                        KEY(0X09);
                        SETKEYSTAT();
                        break;
                }
                case(0x02): {
                        while(PORTB == 0x02);
                        PRESS++;
                        KEY(0X00);
                        SETKEYSTAT();
                        break;
                }               
            };  
        }       
 
        if(KEYSTAT)
        {
            if(PRESS == 1)
            {
                LCD_COMMAND(0XC0);
                LCD_DATA('*');
            }
    
            if(PRESS == 2)
            {
                LCD_COMMAND(0XC1);
                LCD_DATA('*');      
            }
    
            if(PRESS == 3)
            {
                LCD_COMMAND(0XC2);
                LCD_DATA('*');
            }
    
            if(PRESS == 4)
            {
                LCD_COMMAND(0XC3);
                LCD_DATA('*');      
            }
        }
 
        if((PORTC & 0x04) == 0x04)
        {
            while((PORTC & 0x04) == 0x04);
    
            if((NUMBER[0] == 0X04) && (NUMBER[1] == 0X01) && (NUMBER[2] == 0X00) && (NUMBER[3] == 0X04))
            {
                if(LOCK == 0)
                {                   
                    LCD_COMMAND(0X80); 
                    LCD_STRING("LOCKED");
                    PORTE = 0X01;
                    __delay_ms(2000);
                    PRESS = 0;
                    LOCK = 1;
                    INITIAL();
                }
                else
                {                    
                    LCD_COMMAND(0X80); 
                    LCD_STRING("UNLOCKED");
                    PORTE = 0X02;
                    __delay_ms(2000);
                    PRESS = 0;
                    LOCK = 0;
                    INITIAL();
                }
            }
            else
            {
                LCD_COMMAND(0X80); 
                LCD_STRING("WRONG PASSWORD");
                __delay_ms(2000);
                PRESS = 0;
                INITIAL();
            }
        
        }
 
        if(PRESS == 0)
        {
            for(i = 0; i < 4; i++)NUMBER[i] = 0x00;
 
            i = 0;
        }
 
        if((PORTC & 0x04) == 0x04)
        {
            while((PORTC & 0x04) == 0x04);
    
            PRESS = 0;
            INITIAL();
        }
    }
}
 
void LCD_COMMAND(char cmd)
{
    PORTD = cmd;
    RA2 = 1;
    RA2 = 0;
    __delay_ms(10);
}
 
void LCD_DATA(char dat)
{
    PORTD = dat;
    PORTA = 0b000001;
    PORTA = 0b001101;
    PORTA = 0B000001;
    __delay_ms(10);
}
 
void LCD_STRING(char *str)
{
    while(*str)LCD_DATA(*str++);
}
 
void KEY(unsigned char TEMP)
{
    switch(PRESS)
    {
        case 1:
            NUMBER[0] = TEMP;
            break;
        case 2:
            NUMBER[1] = TEMP;
            break;
        case 3:
            NUMBER[2] = TEMP;
            break;
        case 4:
            NUMBER[3] = TEMP;
            break;
    };
}
 
char ASCII(char temp)
{
    if(temp > 0x09)
    {
        temp = temp + 0x07;
    }
 
    temp = temp + 0x30;
    return(temp);
}
 
void INITIAL(void)
{
    LCD_COMMAND(0X01); 
    LCD_COMMAND(0X0C); 
    LCD_COMMAND(0X80);
 
    LCD_STRING("ENTER PASSWORD");
    LCD_COMMAND(0XC0);
}
 

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