JPS6476201A - Fail safe device for control system for vehicle - Google Patents

Abstract

PURPOSE:To restart the operation of a control system and to prevent the control system from keeping an unnecessary rest condition by providing a means to release fail safe function at the self-reset time of a microcomputer. CONSTITUTION:After a microcomputer 10 is activated, when abnormality is detected by a supervising part 4, a contact 3a is opened through transistors 5, 5 and 7, etc., and an abnormal control signal is supplied to a driving part 1. Then, control is prevented from being at random. However, when the abnormality is the temporary run-away of the computer 10 by a noise, self-reset is executed by a watch dog timer 13 and the signals of 0,1,0,1 are outputted from ports P0-P3 for a constant time. These signals keep the output of an AND gate 14 at a medium-high level for the constant time and close the contact 3a, simultaneously, this condition is self-held and after the constant time, even when the computer 10 wholly causes the output of the respective ports to be zero level, the contact 3a is kept in a closing condition. Thus, the prescribed control is restarted and the unnecessary rest condition is prevented.