The ongoing advances being made in electronics technology has made it possible to expand the range of microcomputer applications in automotive engine control systems. Progress in this field of application has given rise to very sophisticated control systems called total engine control systems, which are designed to provide interacting control with other subsystems (e.g., antiskid braking system, traction control system, transmission control system), instead of just controlling the engine itself. Improved engine control system performance and more versatile functions have made the application software controlling the system larger, with more complex control processing.Until now, control processing in engine control systems could be implemented by the microcomputer's interrupt processing program alone. However, because engine control systems have grown in both size and complexity, it has become difficult to determine the sequence in which processing programs (tasks) are to be executed. Consequently, the basic software (realtime operating system) that efficiently makes this determination has become necessary.This paper describes the use of microcomputers in engine control systems by using our newly developed μPD78602 16-Bit Single-Chip Microcomputer that incorporates a realtime operating system as firmware (alias Realtime Task Manager: RTM) as an example.