Score Counter

Entry posted by DanBoris July 23, 2006

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The first step in counting the score is to determine when one player or the other has missed the ball. This turns out to be very easy to detect because the only graphic object that can move off the visible screen is the ball. The circuit shown below ANDs the horizontal component of the video with the HBLANK signal to create the /MISS signal. Whenever there are graphics being displayed during horizontal blank, /MISS will go low indicating that the ball went off the screen. /MISS next passes through E1 where it is ANDed with /ATTRACT, this prevents the scores from incrementing during the attract mode. The final output signal is /MISSED which goes low when the ball is missed.

The next parts of the score counter are two almost identical circuits that are used to keep track of the score, one for each player. When L is low, it means that the ball is moving right. When MISSED goes low indicating that the player missed the ball, the output of F5 will go high which will increment the score counter C7. The counter is actually composed of two chips, C7 which is a decade counter (which means it counts 0 to 9) and J/K flip flop C8 which provides the 10’s digit of the score. The final function of this circuit is to determine when the game is over based on the score. Pong can be configured to play games up to a score of either 11 or 15, this is set by switch SW1A. When the switch is in the 11 position, D8 ANDs together the 1 and the 10 output of the counter thus ending the game at 11. When the switch is in the 15 position, D8 ANDs together 1, 4 and 10, ending the game at 15. When the end score is reached /STOPG1 goes low ending the game