Okay, you've lost me. :huh: All you do is increment the LY register every 456 cycles, and reset it to 0 once it hits 154. The mode flag has nothing to do with it. You don't actually draw the lines after 143, they are just the time it takes for the screen projector to reset to it's starting position. Though, games use the LY register to verify if they are in the V-Blank or possibly how far along the V-Blank is. Also, you might want to consider using machine cycles rather than clock cycles. It's basically the cycle timings divided by 4. So, instead of having 456 cycles for a line, you would have 114. It wouldlet you use smaller numbers.