Looks like we have finally come to the last Pong circuit we need to cover. I just looked back at the archive for this blog and was shocked when I realized that I have been doing this Pong circuit description for almost 2 years! I know I was going through this pretty slowly but never realized I had taken that long. On to the final circuit...

This circuit is used to generate a sound whenever the ball hits the top or bottom of the screen. During normal play /SERVER is high so the flip/flop won’t be cleared. When the vertical portion of the ball video (VVID) is high in the VBLANK area the ball has gone off the top or bottom of the screen which will cause the Q output of F3 to go high. This will allow VPOS32 to pass through C3 to generate the hit sound. When the ball leave the VBLANK area, VVID will be low during VBLANK setting Q low and turning off the sound. Between serves the /SERVER signal will be low keeping the Q output of F3 low. This prevents the ball from making the hit sound as it is move into position for the next serve.