Field presettable electronic odometer

Abstract

A microprocessor is utilized to store a total accumulated driven mileage (odometer) signal in a non-volatile random access memory (RAM). Trip mileage manual pushbuttons are coupled to the microprocessor and enable the calculation and display of elapsed driven mileage (trip mileage), and a units pushbutton converts the displayed total accumulated driven mileage and/or the elapsed trip mileage from a miles to a kilometer visual display. The microprocessor effectively retrieves non-volatile stored odometer signals, loads them into a microprocessor volatile memory, increments the volatile memory mileage signal in accordance with signals from an actual mileage sensor and provides a visual mileage display on an odometer display. The magnitude of the odometer signal stored in the non-volatile memory can be preset to a predetermined mileage after the non-volatile memory is coupled to the microprocessor. This presetting can only be implemented a maximum of three times and only if a non-volatile, non-presettable actual mileage memory indicates the vehicle has been driven less than ten miles. In response to a substantial adjustment of the non-volatile stored odometer signal, an overflow flag is non-volatilely stored and the odometer display provides a visual indication that this adjustment has occurred whenever the odometer display provides a visual indication corresponding to the total accumulated mileage. The presetting of the odometer signal in the non-volatile RAM is accomplished through utilization of the trip and units manual controls, and the vehicle ignition switch.