Sorry, i can't still figure uit what i need to do... What I want to do is negate the variable speed. That's all! Only if I knew how.... This is what I tried: call _zerooop1 ld a,(speed) ld (op1),a call _invop1s call _convop1 ld a,e ld (speed),a Can anybody tell me what's wrong with it? (Probably everything) Thanx, Marc