Method and apparatus for storing main data with two checkup data

摘要

An electronic control unit has a microcomputer and a backup RAM, which stores its data irrespective of ON/OFF of an engine ignition switch. The backup RAM stores a main data in its storage area, and two checkup data in its storage areas, respectively. The two checkup data are calculated as a two-byte data from the main data of a 4-byte floating points type data and equal to each other. The microcomputer executes a data storing operation in the order of one checkup data, the main data and the other checkup data. The microcomputer determines that the main data is correct when either one of the checkup data is determined correct.