Ball Horizontal Control (Part 1)

Entry posted by Guest November 24, 2005

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The purpose of this circuit is to generate the Aa and Bb signals that go into the horizontal ball counter. I will describe what this circuit does first, and then go into the details of how it does it. There are three valid states for Aa,Bb:

Bb Aa

0 1 - move left

1 0 - stationary

1 1 - move right

Normally the Aa/Bb outputs will be in the stationary state, because we only want the ball to move a little bit on each frame, so for most of the horizontal lines the ball is not moved. At the start of each video frame either the move left, or move right state is select and stays select for 1, 2 or 3 lines. The more lines it stays enabled for the faster the ball will move in one direction of the other.

The circuit that generates Aa/Bb has two parts, we will look at the second part first.

The flip/flop H3 is used to control the direction of the ball. When the ball hits the left paddle, /HIT1 will go low, which will set pin 9 of H3 high, indicating a left hit. When the ball hits the right paddle, /HIT2 will go low, which will set pin 8 of H3 high, indicating a right hit. When MOVE is low, Aa will be 0 and Bb will be 1 which keeps the ball stationary. When L and MOVE are high, Aa will be 1 and Bb will be 1 which causes the ball to move right. When R and MOVE are high, Aa will be 1 and Bb will be 0 which causes the ball to move left. We will discuss the function of the CLK input to H3 in a later.

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