How to set a bit(s) [AVR programming]

We want to set pins 0,2,5 to low and 1,3,4,6,7 to high.

How?

• Binary number (works only on certain gcc compilers)

  PORTD = 0b11011010;

• Hexadecimal number
  

  PORTD = 0xDA;

Changing a value of a specific bit to high. Let’s assume, our register looks like PORTD: 11011010 and we want only to change the value of the 2^nd bit to one. We can use Boolean algebra disjunction like

PORTD |= (1 << bit_number);

In this case:

// set second bit high
PORTD |= (1 << 2);

11011010
00000100 |
11011110 (result)

We can also change several bits at the same time:

// sets pin 4 and 5 to logical one
PORTD |= (1 << 4) | (1 << 5);

Changing a value of a specific bit to low. It works almost the same as in the example above, except that logical conjunction and negation is used. When changing 3^rd bit of PORTD to zero, the pattern looks like:

PORTD &= ~(1 << bit_number);

So: 

//sets third bit low
PORTD &= ~(1 << 3);

11011010
11110111 &
11010010 (result)

To change more than one bit, we use:

// sets pins 6 and 7 to logical zero
PORTD &= ~((1 << 6) | (1 << 7));