Here is the circuit that keeps track of whether a game is running. It uses discrete transistors rather than chips to implement a latch. When the coin switch is briefly pressed, it brings SRST high for a short time, and also brings RUN low, which turns off attract mode and starts the game.

When STOP G is asserted at the top left, that turns off the latch and brings RUN high.

The "Antenna" input is intended to prevent free games initiated by a static shock to, say, the coin logic. If you apply a voltage to "Antenna" by clicking the logic input in the lower right, it will stop the game.

A buffer has been added to this circuit to convert from TTL to CMOS logic (since the logic gates in this simulator have a threshold of 2.5 V, but the original circuit used TTL gates).

Next: Serve Timer.