| 摘要 |
PURPOSE:To substitute a storage part for a faulty ROM easily, by applying a modified address, which is obtained by adding the address from an address controlling circuit and the difference between a special address of the ROM and the address of a substitutional instruction, to a substitutional instruction storage part. CONSTITUTION:Controlling micro mu programs are stored in a ROM1, and substitutional instructions which are allocated to an address area other than that of the ROM1 and are substituted for mu instructions stored in a specific address area of the ROM1 are stored in a WCS3. When address information of the specific area of the ROM1 is inputted from an address controlling circuit 2 to a substitution indicating information holding part 4 and an address difference information memory part 5, a substitution indicating signal 7 is outputted from the holding part 4 to an adding circuit 6. Information of the address difference between the start address of the substitution area of the WCS3 and the start address of the specific area of the ROM1 is outputted from the memory part 5 to the circuit 6, and the address difference and the address from the circuit 2 are added, and the result is applied as a modified address to the WCS3 through mu address register 8. The substitutional instruction in the modified address is outputted from the WCS3 and is executed in an instruction discrimination controlling circuit 11. |
