JPH05189227A - Microcomputer incorporating one time programmable rom - Google Patents

Abstract

PURPOSE:To effectively use a microcomputer without abolishing it by writing '00' into the part of program data equivalent to a bug when the bug is detected after program data is once written. CONSTITUTION:'00' in a machine word is set to be a jump instruction to a previously set address. A private vector table part 4 is set in the address, and a jump destination address designation register is provided for the vector data part 4. When the instruction of '00' is read during the execution of a program, a processing is branched to the vector table part 4 and is branched to the address which is set in the jump destination address designation register in the vector table part 4. Since the head address of a correction program data part 3 is set in the jump destination address designation register, a correction program is executed. When it is terminated, the processing is executed again immediately after the bug part 2 of an original main program.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-time programmable (OneTime) program capable of correcting a bug in a program.
The present invention relates to a microcomputer with a built-in programmable ROM.

[0002]

2. Description of the Related Art Generally, in this type of microcomputer incorporating a one-time programmable ROM, the RO
State before program data is written to M, that is, R
When expressed in hexadecimal notation, the initial state of OM is "FF, FF,
FF, ..., FF ”, which can be expressed in binary notation as“ 11111111, 11111111, 111 ”.
11111, ..., 11111111 ”. When the program data is written in the ROM in such an initial state, "1" is rewritten to "0" depending on the contents. Once the program data has been written in this way, "1" can be rewritten to "0" again, but "0" cannot be rewritten to "1".

[0003]

Such a one-time programmable ROM built-in microcomputer is optimum for a small quantity and a large variety of devices. But,
If the program data is once written in the ROM and then a bug is found in the written program, it cannot be changed, so there is a drawback that it cannot be effectively used and is discarded. It was

[0004]

In order to solve such a problem, the present invention cannot change "0" data to "1" data when a bug is discovered after the program data is once written. , "1" data can be changed to "0" data, and "00" is written in the portion of the program data corresponding to the bug to correct the bug portion.

[0005]

Therefore, even if a bug is found after the program data is once written, the bug can be corrected, and as a result, the microcomputer can be effectively used without being discarded.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows a one-time programmable R according to the present invention.
It is a block diagram which shows one Example of the microcomputer with a built-in OM. This figure shows the arrangement of program data in the one-time programmable ROM built in this microcomputer, where 1 is the main program data part, 2 is a bug part indicating a defective part of the main program, and 3 is a bug part. 2 is a modified program data section that modifies the program data of 2.

Generally, in this kind of microcomputer having a built-in one-time programmable ROM, even if the program data is written in the ROM, an empty area still exists in the ROM. Therefore, the correction program data section 3 is provided in an empty area where the program data is not written, and the correction program data of the bug section 2 is stored when a bug is found in the main program data section 1. Is. As a result,
When the main program is sequentially executed from the head address and reaches the bug section 2, the program branches to the modification program data section 3 to execute the modification program, and when the execution of the modification program ends, the program branches to the main program immediately after the bug section 2. Then the processing is continued.

FIG. 2 is a diagram showing a concrete branching situation when the main program is executed. Here, "00" in the machine language is a jump instruction to a preset address. A dedicated vector table unit 4 is set at this address, and a jump destination address designating register is further provided at this vector table unit 4. When the program data in the main program data unit 1 is read and the instruction "00" is read during sequential execution, the process branches to the vector table unit 4 and the vector table unit 4
Further branches to the address set in the jump destination address specification register. Here, the leading address of the correction program data section 3 is set in the jump destination address designating register.
Therefore, the programs stored in the correction program data section 3 are sequentially executed from the head address. And
When this is finished, again the bug part 3 of the original main program
The process is executed immediately after. That is, the address immediately after the bug part 2, that is, the address of the return destination is set at the end of the correction program data part 3.

That is, when a bug is found in the program data once written in the ROM, "00" is written in the head address of the bug section 2 and the correction program data and the instruction to restore the program immediately after the bug section 3 are issued. Is written in an empty area where writing has not been performed, so that a bug in the program is corrected.

[0010]

As described above, according to the present invention,
Even if a bug is discovered after the program data is once written, it can be corrected, and as a result, the microcomputer can be effectively used without being discarded.

[Brief description of drawings]

FIG. 1 is a one-time programmable ROM according to the present invention.
It is a block diagram which shows one Example of a built-in microcomputer.

FIG. 2 is a diagram showing an execution status of a program in which a bug is corrected in the microcomputer.

[Explanation of symbols]

 1 main program data part 2 bug part 3 correction program data part 4 vector table part

Claims (1)

[Claims] 1. A means for storing "00" data at the head address of the bug portion when a bug is found in the program data once written in a microcomputer with built-in one-time programmable ROM in which the program data cannot be rewritten. And means for storing the program data in which the program data of the bug portion is corrected in an area other than the area in which the program data is written, and storing return instruction data to the program immediately after the bug portion. One-time programmable ROM characterized by
Built-in microcomputer.