A method and apparatus for controlling the various functions of an internal combustion engine using a program-controlled microprocessor having a memory preprogrammed with various control laws and associated control schedules receives information concerning one or more engine-operating parameters such as manifold absolute pressure, throttle position, engine coolant temperature, air temperature, and engine speed or period or the like. These parameters are sensed and then supplied to input circuits for signal conditioning and conversion into digital words usable by the microprocessor. The microprocessor system computes one or more digital command word indicative of a computer-commanded engine control operations and output circuitry responds to predetermined computer-generated commands and to the computed digital command words for converting them to corresponding pulse width control signals for controlling such engine operations as fuel-injection, ignition timing, proportional and/or on-off EGR control, and the like.
More particularly this disclosure relates to an improved microprocessor-based engine control system for controlling both fuel and ignition wherein an exhaust gas sensor is periodically sampled for the integrity of its output signals. In addition, an A/D converter having a novel window which is used in the engine control system and the digital control of ignition signals is also described.