US Patent 7142627 Counting scheme with automatic point-of-reference generation

A counting scheme for a non-volatile counter includes automatic point-of-reference generation implemented in a state machine. Two state variables are used to store the rotation history of the magnet. One variable stores the previous position of the magnet and the other stores the net angle traveled by the magnet from the reference point. The first pulse location after the counter is reset is automatically selected as the reference point until the next counter reset. When the nonvolatile counter counts up or down, i.e. when the magnet travels 360° in either direction, the second state variable is set to zero and the first state variable is set to the reference point, indicating the start of a new revolution.