On 3/7/07, Mauricio Jancic <info@janso.com.ar> wrote:

> if(!(PINB & (1<<PB1)))
>
>         Whats that? Specially the (1<<PB1) that I cant seem to figure out...

The statement "x << y" means "take the number x and rotate its bits y
times left". If PB1 in your example is 5, then "1<<PB1" would mean "1
<< 5", which in binary is "00000001 << 5", which finally gives the
result "00010000".

Next step (going from the innermost parenthesis and out) is "PINB &
(the above)", which is a logical AND-function. AND returns 1 at those
bitpositions where both are 1s. "111000 & 000111" is zero, while
"111000 & 001000" is 8 (1000 binary).  For the sake of the argument,
if the value of PINB has a "1" at the same position as the result from
above will be the same as (1 << PB1).

And finally, the "!" inverts the whole parenthesis.

What the if does is checking if the particular bit in PINB is set or
not. If it's not set, the code will proceed into the if's then-clause.


-- 
- Rikard.
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