The sequence of operations for playing the game between, say two players “X” and “Y”, is summarised below:
1. Player “X” starts by momentary pressing of reset switch S1 followed by pressing and releasing of either switch S2 or S3. Thereafter he presses switch S4 to read the display (score) and notes down this number (say X1) manually.
2. Player “Y” also starts by momentary pressing of switch S1 followed by pressing of switch S2 or S3 and then notes down his score (say Y1), after pressing switch S4, exactly in the same fashion as done by the first player.
3. Player “X” again presses switch S1 and repeats the steps shown in step 1 above and notes down his new score (say, X2). He adds up this score to his previous score. The same procedure is repeated by player “Y” in his turn.
4. The game carries on until the score attained by one of the two players totals up to or exceeds 100, to be declared as the winner.
Go to that page to read the explanation about above circuit design.