C - AVR - Simple PORTB, DDRB, PINB explanation

Question

I am working on school project and need to learn the basics of C with a AVR atmega controller.

I don't understand how everything is set up. For example PORTB, PORTD, DDRB; DDRD, PINB, PIND and stuff like that. And I don't know how everything works with if statements, while loops, etc.

Can someone give me a short explanation please?

I have a few code lines...

Click to copy

DDRB = 0b00000011; // I know that here DDRB is set to input/output

And an if statement:

Click to copy

if (PINB & (1 << PINB0)){
    A = true;
}

Can someone explain me how this 'if statement' works? Why PINB & (1<< PINB0))?

Thanks

Answer 1

Do you means what is if-condition PINB & (1<< PINB0))?

It checks whether PINB0 + 1 number bit( from rhs) is ON (1) in PINB or OFF (0).

For example. (a & (1 << 2)) checks whether 3rd bit is ON in a or OFF. In the expression two operators are used << bitwise left shift and & bitwise and below I have explained for one byte example:

1. 1 is 0000 0001
2. 1 << 2 after left shift gives 0000 0100

3. a bitwise and with 0000 0100 gives either all zeros 0000 0000 or 0000 0100

   3a. If all zeros then if condition is false (when third bit in a is zero).
   3b. If result of bitwise and is 0000 0100 then if condition evaluates as true (when third bit in a is one).