Vehicle detector with power failure information saving

Abstract

A method and apparatus for storing reference information in a non-volatile memory unit when a power loss to a vehicle detector is imminent. A power monitor circuit senses an impending power loss. In response, the vehicle detector transfers reference information, including a reference count and the number of loop cycles over which the reference count was accumulated, as well as optional detector status information, from the vehicle detector volatile memory (typically RAM) to the non-volatile memory unit. When power is resumed, the information stored in the non-volatile memory unit is restored to the vehicle detector. The restored information prevents improper and potentially dangerous vehicle detector operation caused by the loss of reference information during unpredictable power losses. The transfer operation is not performed if the power loss is due to a mechanical disconnection of power. By limiting the information transfer operation to only an impending power loss condition, the use of non-volatile memory to store the information is made practically feasible.