Thank you for your answer, I think I corrected that part but now, I cannot get anything out from the block ram. I wrote the code for comparing datas from the other 2 roms and then write the desired data to a block ram. I simulated it, In simulation, the bits are correct and I can read them but when I connect the vga, then I only get black screen (i check the sync signals, i can get green screen and such). So i thought maybe the timing is wrong, because at the time vga starts, the comparison between the roms are made and the data is not ready yet in the block ram. What can I do? How can I read