INDEX

The above figure shows the internal circuit diagram of 555 as an astable multivibrator. In this there are two comparators with its +Vcc=Vcc of 555 and -vcc=gnd. See comparator explanation in opamp section. Next comes the R-S latch. Pin4 of 555 is reset which will reset the latch irrespective of the inputs(R,S),i.e Q=0 and Q'=1

When R=S=0 then the output will remain same as the previous value. A latch is used to store one bit of information, so if no input then output will remain as the previous value, no input means R=S=0. When R=S=1 then Q=1 and Q'=1, this is not a desired case because when Q=0,Q'=1 and when Q=1,Q'=0 according to the logic.