AVR C - Why inverting values?

Question

I have extremly stupid question, but I wasn't able to find answer to it. I am starting AVR programming and I have one question, regarding code example I've found.

int main(void)
{
    DDRA = 0xFF; // Setting all port A pins for output

for(;;)
{
    PORTA = ~0x21; // Why ~ if we want PA0 and PA5 to be High?
    _delay_ms(10000);
}

So why we need to invert 0x21? It should have High on PA0 and PA5, but if we are inverting it, shouldn't it be the opposite (all High except for PA0 and PA5)?

I have tried to search, but I haven't found any explanation. Thank you!

Answer 1

The issue was with me looking only into code. You should also always check scheme to see how UC is connected.

In my case it was "inversive" way of connection, where "0" meant LED turned on.