JP2844901B

PURPOSE:To precisely diagnose a failure by determining output conditions of switching elements in accordance with serial signals so as to diagnose a failure. CONSTITUTION:An I/O unit 100 receives serial data delivered from an SOUT terminal of a microcomputer (MC) 200, in synchronization with clock pulses delivered from an SCLK terminal of the MC 200, and changes levels to at Q1 through Q2 of the unit 100 so as to energize a step-motor 300. Further, the unit 100 detects turn-on and -off of the motor 300, and serial data as a result of detection is delivered from the SOUT terminal of the unit 100 to an SIN terminal of the MC 200 which therefore diagnoses a failure of this signal. Further, the MC 200 and the unit 100 are fed with a voltage from a 5V constant voltage source, and are turned on when signals from a power-on and reset signal generating device 400 are taken through INIT terminals.