Q.What is a counter?

A counter is a sequential circuit that counts the number of clock pulses applied to it, moving through a fixed sequence of states with each pulse. Counters are built from flip-flops — an n-flip-flop counter can count up to $2^n$ states — and they are used for frequency division, digital clocks, event counting and control-sequencing.

Counters are broadly classified as asynchronous or synchronous. In an asynchronous or ripple counter, only the first flip-flop receives the external clock; each following flip-flop is triggered by the output of the flip-flop before it. Because the change ripples through the chain, each stage adds a small delay, and these delays accumulate, which limits the maximum counting speed and can cause momentary false counts in large counters. …