Interfacing 4x4 keypad with PIC16F877A in CCS...

[Athar Rasul]

hi,
I am interfacing the keypad on a single port using B0-B7. I am having problem with the key detection.. kindly help.

 int keypad(){
	int i; int key=0;
	output_B(0x01); // Start with column 1
	while((input_B() & 0xF0) == 0){ // While no key pressed
		output_B(input_B() << 1); // next column
		key++; // column number
		if(key==4){
			output_B(0x01); // Back to column 1
			key = 0;
		}
	}
	delay_ms(20); // Switch debounce

	for(i=0x10; i!=0; i<<=1){ // Find the key pressed
		if((input_B() & i) != 0)break;
		key=key+4;
	}
	output_B(0x0F);
	while((input_B() & 0xF0) != 0); // Wait until key released
	delay_ms(20); // Switch debounce
	return (key); // Return key number
}

 

[cool.man]

I have used 4*4 keypad and following is my routine.You can use this routine

while(1)
{
 value=readkeypad();
 printf("%d",value)
}

int readkeypad (void)
{
 output_bit (r1, 0);
 output_bit (r2, 0);
 output_bit (r3, 0);
 output_bit (r4, 0);
 output_bit (r1, 1);//activate 1st row and scan for column
 delay_ms(10);
 IF (input (c1)) RETURN 10;
 IF (input (c2)) RETURN 0;
 IF (input (c3)) RETURN 11;
 IF (input (c4)) RETURN 12;
 output_bit (r1, 0);//Deactivate 1st row
 output_bit (r2, 1);//activate 2nd row and scan for column
 delay_ms(10);
 IF (input (c1)) RETURN 7;
 IF (input (c2)) RETURN 8;
 IF (input (c3)) RETURN 9;
 IF (input (c4)) RETURN 13;
 output_bit (r2, 0);//Deactivate 2nd row
 output_bit (r3, 1);//activate 3rd row and scan for column
 delay_ms(10);
 IF (input (c1)) RETURN 4;
 IF (input (c2)) RETURN 5;
 IF (input (c3)) RETURN 6;
 IF (input (c4)) RETURN 14;
 output_bit (r3, 0);//Deactivate 3rd row
 output_bit (r4, 1);//activate 4th row and scan for column
 delay_ms(10);
 IF (input (c1)) RETURN 1;
 IF (input (c2)) RETURN 2;
 IF (input (c3)) RETURN 3;
 IF (input (c4)) RETURN 15;
 output_bit (r4, 0);//Deactivate 4th row
 RETURN 255;
}

 

[samson A.]

Man. Why are you bothering your head. The CCS compiler has got an keypad inbuilt library(KBD.C) in the driver folder. include it in your project...