> If I go UP slowly the increment is sometime by 2 ?
> If I do DOWN sometimes the increment is by 1 !

This sounds like you are missing one of the state transitions and assume things are increasing. If you need some logic that determins the direction of travel -- possibly by looking at the direction just before the transition was missed. This might be harder if you slept.

Also, You should make your reads of A and B atomic (one operation.) Read the whole port and extract the pieces from that. I would also go in a loop and only use the paired values when they match a previous read. This is even _before_ doing real debouncing code. Do something like...

int getAB()
{
int sample1 = in(portX) & A_B;
int sample2;
while ( (sample2= in(portX) & A_B) != sample1 )
sample1 = sample2;
return sample1;
}


<>< Lance.