This is done by pressing the switch (when the switch contacts are shorted the trigger input is connected directly to ground and therefore will have a voltage of 0V). To start the monostable the trigger voltage needs to quickly be dropped to 0V.

The trigger input is at 9V (due to the pull-up resistor R1).

The flip flop output voltage is therefore 9V.

Both comparators inside the 555 chip have 0V on their outputs to the flip flop.

The voltage across the capacitor C1 is 0V.

All unused inputs must be tied to an appropriate logic level to prevent false triggering.In the starting state of the circuit the following is true Whenever the output is low, a low-impedance path is provided between the discharge terminal (DISCH) and GND. If RESET is low, the flip-flop is reset and the output is low. The reset input (RESET) can override all other inputs and can be used to initiate a new timing cycle. If TRIG is above the trigger level and the threshold input (THRES) is above the threshold level, the flip-flop is reset and the output is low. When the trigger input (TRIG) falls below the trigger level, the flip-flop is set and the output goes high. These levels can be altered by use of the control voltage terminal (CONT). Like the NE555, the TLC555 has a trigger level equal to approximately one-third of the supply voltage and a threshold level equal to approximately two-thirds of the supply voltage. Power consumption is low across the full range of power-supply voltage. As a result, more accurate time delays and oscillations are possible.

Because of its high input impedance, this device supports smaller timing capacitors than those supported by the NE555 or LM555. The timer is fully compatible with CMOS, TTL, and MOS logic and operates at frequencies up to 2 MHz. The TLC555 is a monolithic timing circuit fabricated using the TI LinCMOS™ process. Configuration control and print support.High-reliability automotive applications.ESD protection exceeds 2000 V per MIL-STD-883C, method 3015.2.Functionally interchangeable with the NE555 has same pinout.Single-supply operation from 2 V to 15 V.Low supply current reduces spikes during output transitions.Output fully compatible with CMOS, TTL, and MOS.CMOS output capable of swinging rail to rail.

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