An asynchronous counter is a sequential circuit where flip-flops are triggered sequentially by the output of the previous flip-flop, causing a ripple effect.

The main difference is that in synchronous counters, all flip-flops are triggered by the same clock signal, while in asynchronous counters, flip-flops are triggered sequentially.

Asynchronous counters are simple, cost-effective, and require fewer components, making them suitable for basic counting tasks in digital circuits.

A MOD-N counter is a counter that resets after counting up to a predefined number, N, cycling through N states before resetting to 0.

A 3-bit asynchronous up counter uses three flip-flops to count in increasing order, typically from 0 to 7.