TETRIS

The pieces for the game are stored in ROM so they can be loaded onto the screen at anytime. When a piece is loaded it is stored in First Comparator Memory, This is where all falling blocks are stored. Every clock cycle the pieces stored in this Comparator Memory will be moved to the cell below it. The Clock starts at the bottom and works its way up to prevent the blocks overlapping. If the left/right movement input is activated, the falling blocks will move either left or right instead of falling straight down. Due to this being quite slow, there is a "Fast Drop" which will drop the piece but you wont be able to move left/right. Rotation occurs before the piece is dropped, the player can choose when the piece drops, so having as much time to think about which way you want the piece to be rotated doesn't make the game any more difficult to the real version. The pieces cannot move outside of the screen, if you try move the the piece to the right while it is pressed up against the right side, it will simply fall straight down. This is also true for if you try to move a piece against another piece. When a piece lands on a solid piece, it is moved from the Falling Memory to the Solid Memory and will no longer fall. When a line is filled in it will be removed and all the line above it will be moved into the Falling Memory(Some pieces appear missing at first, give it a few seconds and they will reappear).