The circuit operates as follows:
1. In this circuit's initial condition, the capacitor C is held discharged through the discharge pin, which is grounded in the timer. The threshold voltage is equal to the voltage across the capacitor.
2. When the trigger pin receives a negative trigger pulse less than 1/3 Vcc, the flip-flop sets the output to high and disconnects the discharge pin from the ground. This allows the capacitor to charge until the voltage across it reaches 2/3 Vcc, which takes about