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Once the key pressed the while loop is executed even without pressing again

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thannara123

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I have a program to ON and OFF a device , the following program [MPLab Pic16f877a controller Simulation on Proteus)


string("Press to ON ");
__delay_ms(500);
while(PORTDbits.RD7==0);
while(PORTDbits.RD7==1)
{
PORTDbits.RD7==0; // flush again the press

// working code
}

First it will operate normally ,and the second iteration the while loop excuted without pressing my RD7 switch .

what is the reason ?
 

1.jpg



Port Setup
void main(void)
{ start:

TRISD7 = 1; // A as input
TRISD5 = 1; // A as input
TRISD6 = 0;
UD[0]=65,UD[1]=66,UD[2]=67 , UD[3]=89; //Data Packet ABC Y
//OPTION_REG &= 0x7F;
TRISB =0x00;
TRISD = 10100000;
__delay_ms(100);
lcd_init();
TRISC6=0; //Output (TX)
TRISC7=1; //Input (RX)

unsigned char data = 0x31;
unsigned int a = 0x01;
unsigned char ch;
ser_int();
Enlarged Image
 

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First it will operate normally ,and the second iteration the while loop excuted without pressing my RD7 switch .
We don't see how second iteration can occur because the overall code isn't shown. After button release, code execution continuous below the loop statement.
 

string("Press to ON ");
__delay_ms(500);
while(PORTDbits.RD7==0);
while(PORTDbits.RD7==1)
{
PORTDbits.RD7==0; // changed it to PORTDbits.RD7 = 0; // Typing mistake changed to assignment operator now working

// working code
}

PORTDbits.RD7 = 0; // Typing mistake changed to assignment operator now working
but why the switch is not go to low when realse the button ?
 

Hello,

TRISD7 = 1; // A as input
TRISD5 = 1; // A as input
TRISD6 = 0;
.
.
TRISD = 10100000;

The last line is sufficient and more compact

PORTDbits.RD7==0; // changed it to PORTDbits.RD7 = 0

The == is a very big error, and if RD7 is a simple input port bit without special useage (interrupt or else) this write command has no sense
 

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