In case you are interested, the operation of the 555 is pretty straight-forward.
It consists of a set-reset flip-flop, with the inputs being level sensitive.
The FF is set when the TRIG input goes below 1/3 Vcc and it is reset when the THRS signal goes above 2/3 Vcc.
When reset, the DIS pin is connected to ground through an open-collector transistor, which can be used to discharge the timing capacitor at the end of the timer period.
The above info is all you need to understand the basic operation of the 555 in most of the common, astable, and one-shot circuits.