When push button is pressed,C1 will start charging through 2x 1kOhm .When the voltage across C1 rises above 2 of 3 is the supply voltage the internal Flip Flop toggles . The discharge pin becomes low & C1 starts discharging. When the voltage across C1 goes below 1of 3 of supply voltage the internal Flip Flop resets & discharge pin goes high. The C1 again starts charging.All this will take place if the IC is healthy.
