Q. Describe the working of bistable multivibrator

A bistable circuit is one which can exit indefinitely  in either of two stable states and which can be induced to make an abrupt transition from one state to the other by means of external excitation. Bistable Multivibrator is a two stage regenerative amplifier.Such interconnected amplifiers pairs are known as Eccles Jordan circuit, Flip-Flop and Binary. Bistable Multivibrator has 2 astable states. Only the application of a suitable trigger pulse makes the circuit to change to the other stable state.Thus one trigger pulse causes the multivibrator to flip from one state to the another and the next pulse causes it to flop back to its original state.

As shown here, the circuit we're looking at really is nothing more than two basic inverters, each taking its input from the other's output. If, when power is first applied, Q1 turns on, its output will be a logic 0. This will be applied to Q2's input resistor, keeping Q2 turned off so that its output will be a logic 1. This logic 1 will be applied back to Q1's input resistor, keeping Q1 turned on and holding the entire circuit locked into this stable state.