The next section I am going to talk about is the score generation circuit. In Pong, each player has a two digit score that is displayed at the top of the screen on either side of the net. The circuit that generates the score display is a little complex, but I find it to be a very interesting design. I am going to start from the center of the circuit and work out.

At the heart of the score generator is as 7448 BCD to 7-segment decoder chip.

This chip is usually used to drive 7-segment LED numeric displays. The chip takes as an input the binary value of the digit to display. These inputs are labeled A,B,C,D on the schematic. The chip decodes these inputs and sets the appropriate outputs high to drive the segments necessary to form that digit. The segments are identified as follows:

So, if the binary value 7 is put into the chip, it will set outputs a, b, c high. Input values 0 – 9 generate the corresponding digits, values 10-14 are not used in this circuit, and the value of 15 turns off all outputs, we will see how Pong uses this later on. The other pin that Pong uses is pin 4, ~BI/RBO, which when low, turns off all the outputs.