Date of Patent: Dec. 25, 1984
 MICROCOMPUTER WITH SELF-TEST OF MICROCODE
 Inventors: Kevin C. McDonough; Jeffrey D.
Bellay, both of Houston, Tex.
 Assignee: Texas Instruments Incorporated, Dallas, Tex.
 Appl. No.: 280,04a
 Filed: Jul. 2, 1981
 Int. CI.3 G06F 11/00; G06F 7/00
 U.S. a 364/200; 371/38
 Field of Search ... 364/200 MS File, 900 MS File
 References Cited
U.S. PATENT DOCUMENTS
3,517,171 6/1970 Avizienis 364/200
3,959,636 5/1976 Johnson el al 364/200
4,128,873 12/1978 Lamiaux 364/200
4,141,068 2/1979 Mager el al 364/200
4,191,996 3/1980 Chesley 364/200
Primary Examiner—Felix D. Gruber
Assistant Examiner—Daniel K. Dorsey
Attorney, Agent, or Firm—John G. Graham
A microcomputer device contains a CPU with an arithmetic/logic unit and data/address registers on a single semiconductor integrated circuit having on-chip macrocode and microcode storage. A macrocode word is fetched from an on-chip ROM and stored in an instruction register in the CPU, then a sequence of microcode words is fetched from the microcode store based on this macrocode word. A check-code based on some function of all microcode bits, or all macrocode and microcode bits, is stored in on-chip ROM upon manufacture. To test a device after fabrication is complete, a test program (resident in ROM or downloaded into on-chip RAM) is executed to access all bytes of microcode (or both microcode and macrocode) and perform some cummulative function on it via the ALU to see if the same check-code is produced. If so, an output indicates a good unit.
14 Claims, 37 Drawing Figures