One-chip microcomputer system having function for substantially

Abstract

A one-chip microcomputer system includes a one-chip microcomputer, a nonvolatile memory which can electrically rewritably store changing data of a program stored in a mask ROM of the one-chip microcomputer, an input unit (connection unit) for receiving data to be written in the nonvolatile memory from an external device, and an object to be controlled by the one-chip microcomputer. In one aspect, the nonvolatile memory has first and second correction data areas, and first and second memories for respectively designating these areas. Upon reception of an initialization signal from the external device connected to the input unit, only the second memory for designating the second correction data area is initialized. In another aspect, the mask ROM stores ROM version data, and the nonvolatile memory stores board version data. Upon writing of the data via the input unit, bug correction data is selected based on the ROM version data and the board version data, and the selected data is written in the nonvolatile memory. In still another aspect, the nonvolatile memory has a first area for storing data for correcting a bug in the program, a second area for storing data for changing a specification of the object to be controlled, and a third area for determining whether or not data are stored in the first and second areas.