Abstract: A vehicle safety system is equipped with a microcomputer for reliably detecting whether or not programs for controlling activation of passenger protection devices are being properly executed and, based on this detection, preventing problems from occurring in the control operations of the programs. According to one aspect of the invention, the system monitors a program executed on an interrupt basis at prescribed regular time intervals, a repeatedly executed program, and the operations of these programs, synchronously with the execution of the programs, and resets the microcomputer if an error is detected in the execution of either program. According to another, at the time of moving to a subroutine a code peculiar to the subroutine is saved at the entry portion and the saved code is compared with the code peculiar to the executed subroutine at the exit portion for detecting occurrence of error and if error is detected the microcomputer is reset.

Abstract: In a speed detecting apparatus of a vehicle with an internal combustion engine whose rotational output is derived through a transmission, the apparatus comprises a circuit for calculating the gear ratio set in the transmission on the basis of the engine speed and a signal roughly indicative of the vehicle speed and a calculating circuit responsive to the result of the calculation in the circuit and the engine speed at each instant for calculating the speed of the vehicle at each instant. Thus, it is possible to accurately detect the vehicle speed at each instant in a short detection period.