A Cost Effective Microcontroller Based Automobile Instrument Cluster

Dedicated microprocessor systems find increasing applications in automobile instrumentation. Fuel injection systems, digital radio tuners and similar applications employing the microcontroller have become common place. This paper describes a cost effective microcontroller implementation of an automobile instrument cluster by the COPS^TM group of National Semiconductor, Santa Clara. The instrument cluster provides a vacuum fluorescent display of the vehicle speed, engine RPM, odometers, battery voltage, engine oil pressure and the fuel level. A modular design involving a single microcontroller in conjunction with peripherals to aid in data acquisition from the transducers allows the quantities to be computed with high accuracies and displayed on a real time basis. The single microcontroller environment places severe restrictions on the availability of RAM and ROM. Coupled with the requirement of real time operation the application poses a non trivial challenge. A non volatile RAM accumulates the mileage covered. Hamming code techniques ensure the integrity of the data contained in the non volatile memory. Inclusion of diagnostics allows a rapid and thorough check against improper operation of the microcontroller, peripherals and the nonvolatile memory. This paper describes the implementation with a COP 444L containing 128 nybbles of RAM and 2K bytes of ROM. A display updation rate of 16 Hz can be comfortably realized.