How to check if a certain PIN on PORTx is pressed - c

Question

So I have an assignment that wants me to perform certain code when a button on PD2 is presed.
The problem i'am having right now is i don't really know what to check for neither do
i understand the underlying logic.
So this is the code i've come up with thus far.
DDRD=0x00; //PORTD pin 0 as input
PORTD=0x00;
DDRB=0xFF; //PORTB as output
PORTB=0x00;
while(1){
if (PIND & (1<<PD2)==1) // check if PD2 is pressed on PIND2
{
// modify bits on PORTB here
}
}
I'm using Atmega328 and running this on AtmelStudio 7

Answer 1

To set PD2 to an input, run this C/C++ code, which clears bit 2 in register DDRD. There is no need to modify entire registers:
DDRD &= ~(1 << 2);
(You could skip this because every pin will be an input by default after the AVR resets.)
I don't know how you wired your button. If the button is wired between the pin and GND, and there is no external pull-up resistor to pull your pin high, then you should enable the internal pull-up after the pin is an input by running this code, which sets bit 2 in register PORTD:
PORTD |= 1 << 2;
Now to read the state of the button, you can use this C/C++ expression, which will evaluate to 0 if the pin is low or non-zero if the pin is high:
PIND & (1 << 2)
The expression below also works. It has the advantage of always evaluating to 0 or 1:
PIND >> 2 & 1
Here's some (untested) code that ties it all together, reading from PD2 and writing the value of PD2 to an output on PB3:
#include <avr/io.h>
int main()
{
// Make PD2 an input, pulled high.
DDRD &= ~(1 << 2);
PORTD |= 1 << 2;
// Make PB3 an output.
DDRB |= 1 << 3;
while (1)
{
if (PIND >> 2 & 1)
{
// PD2 is high, so drive PB3 high.
PORTB |= 1 << 3;
}
else
{
// PD2 is low, so drive PB3 low.
PORTB &= ~(1 << 3);
}
}
}
You might have to adapt the part of the code that deals with the output. I don't actually know what pin your output is on and what kind of behavior you want, so I just did something simple.
This code is full of the C bitwise operators. It is important for you to get a good book about C and learn exactly what those operators do, and this answer would be too long if I attempted to teach you all of them. Here is a list of operators for you to learn: <<, >>, &, &=, |, |=, ~.

Answer 2

unsigned char input_byte;
while(1){
__no_operation(); /* using nop for synchronization */
input_byte = PIND; /* read entire PIND */
}
This way you should be able to read your inputs every program cycle. But I've not tested this. It's important to use __no_operation() before reading again PIND.