United States Patent  [ii] Patent Number: 4,905,200
Pidsosny et al.  Date of Patent: Feb. 27, 1990
 APPARATUS AND METHOD FOR CORRECTING MICROCOMPUTER SOFTWARE ERRORS
 Inventors: Richard A. Pidsosny, Canton;
Michael J. Burke, Milford, both of
Mich.; Mark W. Jarris, Unionville,
 Assignee: Ford Motor Company, Dearborn,
 Appl. No.: 237,468
 Filed: Aug. 29,1988
 Int CI.* G11C 13/00
 U.S. CI 364/300; 365/201;
365/210, 365/189.07; 365/230.03; 371/11.3;
 Field of Search 365/200, 201, 202, 210,
365/228,189.07,230.03, 230.06; 371/11,13,67,
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Primary Examiner— Terrell W. Fears
Attorney. Agent, or Firm—Allan J. Lippa; Peter Abolins
An apparatus for replacing an undesired code stored in a plurality of storage locations in read-only memory (ROM) with a replacement code. The replacement code, including a jump-back instruction to readdress the ROM, are programmed into an EEPROM. First and second storage locations store the beginning address of the undesired code and the beginning address of the replacement code, respectively. When the beginning address of the undesired code is generated by a program counter, a comparator generates a transfer signal. In response, the beginning address of the replacement code stored in the second storage location is transferred into the program counter. Each address of the replacement code is then sequenced by the program counter until a central processing unit recognizes the jump-back instruction. The central processing unit then readdresses the ROM in response to the jump-back instruction after the entire replacement code has been executed in place of the undesired code.
21 Claims, 3 Drawing Sheets