US Patent 7876873 Asynchronous ping-pong counter and thereof method

An asynchronous ping-pong counter is disclosed. The asynchronous ping-pong counter comprises a first asynchronous counter, a second synchronous counter, and a controller, the asynchronous ping-pong counter operates between a first state and a second state. In the first state, the first asynchronous counter counts a first number of clock edges of a fast clock signal, and the second asynchronous counter holds a first counter output value. In the second state, the second asynchronous counter counts a second number of clock edges of the fast clock signal, and the first asynchronous counter holds a second counter output value. The controller determines a state transition based on a sampling of a slow clock signal by the fast clock signal.