JPS6131902B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for checking whether the contents of a read-only storage device (hereinafter referred to as ROM) in a computer system have changed.

In electronic computer systems, programs and data that do not change during program execution are
Although it is stored in ROM, the contents stored in ROM may change due to mechanical or electrical damage or external conditions. Therefore, in systems that require high reliability, it is necessary to check that the contents of the ROM have not changed at regular intervals during program execution. The present invention is as described above.
It is related to a method for inspecting the memory contents of ROM,
One conventional method for inspecting the storage contents of a ROM will be explained with reference to FIG. ROM is
Assume that three ROMs, ROM1, ROM2, and ROM3, are used. In Figure 1, 1 is ROM
1 and 2 indicate ROM2, and 3 indicates ROM3. A checksum, which is the two's complement of the vertical summation of all the ROM storage contents, is taken and stored at the next address in the ROM 3 that has the largest address. 4 indicates checksum. 5 indicates an address section. When inspecting the ROM storage contents, the checksums of all ROMs are calculated by the storage contents inspection program and compared with the checksums stored in the ROM 3 to determine whether they are normal or abnormal. However, with this method, one of the ROMs in the system
If it is rewritten at any time, the checksums of all ROMs must be rewritten and the checksums must be rewritten. Also, when the ROM is expanded, the address range from which the checksum is taken changes.
The ROM storage content inspection program must be changed.

The present invention solves these problems and allows all
It is an object of the present invention to provide a more reliable method for inspecting the contents of a ROM, which does not require recalculating the checksum of the ROM or changing the program.

An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 2 shows a ROM in an embodiment of the ROM storage content inspection method using the redundant code system of the present invention.
In the configuration diagram, there are three ROM1, ROM2, and ROM3.
Assuming that ROM is used, the start address of each ROM is ADRS1, ADRS2 ADRS
Suppose that it is 3. In Figure 2, 1 is ROM1,
2 indicates ROM2, 3 indicates ROM3, 5 indicates address section, 6 indicates ADRS1, 7 indicates ADRS2, 8 indicates
ADRS3 is shown. The checksums of the three ROMs mentioned above are stored in a ROM dedicated to storing checksums. Let this ROM be ROMZ. Figure 3 is ROMZ
FIG. 2 is a storage content configuration diagram. Each ROM of ROM1, ROM2, and ROM3 is placed at the start address Z.
The start address, the number of bytes representing the number of data, and the checksum are sequentially stored in each ROM as one block using a code that expresses hexadecimal numbers in ASCII code. In other words, the ASCII code is a character code that converts a hexadecimal code into a character code. One 8-bit character represents 128 characters, of which 16 codes 0 to 9 and A to F represent hexadecimal numbers. is used to store in the ROM the content that represents one hexadecimal digit with one character. In FIG. 3, 19 is a block of ROM1, 9 is ADRS1, 10 is the number of bytes of ROM1, and 11 is a range for storing the checksum of ROM2. 20 is the ROM2 block,
12 is ADRS2, 13 is the number of bytes of ROM2, 1
4 indicates the range in which the checksum of ROM2 is stored. 21 is the block of ROM3 and 15 is
ADRS3, 16 is the number of bytes of ROM3, 17 is
Indicates the range in which the checksum of ROM3 is stored.
The order in which ROM blocks of ROM1, ROM2, and ROM3 are stored in ROMZ is arbitrary. All ROMs: ROM1, ROM2, ROM3
Next to the memory range of the block is 0 to 9, A to F.
Remember the end code using an ASCII code other than a hexadecimal code. 18 indicates the storage range of the end code. If you use the ASCII code in this way, you can use the end code, so if you memorize the ROMZ start address and the end code, the ROM storage content inspection program will use the ROMZ start address to determine the start of the ROMZ storage content. The end of ROMZ storage can be determined by the end code. Therefore, the memory content inspection program starts from the start address of ROMZ to ROM1.
The code detects the address and the number of bytes of ROM1, reads it, and calculates the checksum of ROM1.
Comparing the checksum of ROM1 stored in ROMZ with the code detected and read, it is normal.
Determine abnormality. Next, the storage contents of ROM2 and ROM3 are inspected in the same manner as in the case of ROM2, and when the end code is detected and read, the storage contents inspection program is stopped.

In the ROM storage content inspection method using the redundant code system according to the present invention described above, ROM1,
When the contents of one of ROM2 and ROM3 are changed, it is only necessary to rewrite and rewrite only the corresponding checksum. use again
If the number of ROMs increases or decreases, simply change the contents of ROMZ and the position of the end code.
There is no need to change the memory contents inspection program and the check sums of other ROMs. Also, since ROMZ uses 16 codes representing hexadecimal numbers 0 to 9 of the ASCII code and A to F, the ROMZ reading program uses ROMZ for control codes and character codes other than these 16 codes. Since errors in the contents of the ROMZ are detected, the reliability of the ROMZ's own data is higher than that of a program ROM that uses binary numbers. Nuasci code allows the code to have a parity bit, so the reliability of ROMZ can be improved by storing the ROMZ using ASCII code with parity, and by checking the parity in the ROMZ reading program and reading it. It will be even higher. As mentioned above, since the reliability of ROMZ itself is high, if the result of testing using the ROM storage content inspection method using the redundant code system of the present invention shows that the ROM storage content is normal, the reliability is extremely high. Become.

Although the embodiments of the present invention have been explained using ASCII codes, the same effects as in the embodiments can be obtained even when redundant code systems other than ASCII codes are used.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional ROM storage content inspection method, FIG. 2 is a configuration diagram of a ROM in an embodiment of the present invention, and FIG. 3 is a diagram showing a check sum memory in an embodiment of the present invention. Dedicated
FIG. 2 is a configuration diagram of the storage contents of ROMZ of ROM.

Claims (1)

[Claims] 1. In a method of checking whether the memory contents of the ROM of a computer have not changed, a redundant code system is used that uses the start address, number of bytes, and checksum of each ROM of multiple ROMs in use as one block. Store multiple blocks sequentially in a separate ROM from the above using a code that represents a hexadecimal number, and store an end code at the address next to the last block using a redundant code other than the code that represents a hexadecimal number. , ROM storage content inspection involves detecting and reading the start address and number of bytes of the memory content from the start address of another ROM stored above, and reading out the code corresponding to that block.
The checksum of the ROM is calculated, and the result of this calculation is compared with the content read by detecting the code in the stored checksum to determine whether it is correct or not. After comparing and determining all the ROMs, the end code is detected. 1. A ROM storage content inspection method using a redundant code system characterized by ending with .