JPH04195235A - Read-only memory circuit - Google Patents

Abstract

PURPOSE:To detect the abnormality before the start of a program by storing the result of the check sum obtained to the program working with a processor into a storage area of a read-only memory ROM. CONSTITUTION:A ROM 1 consisting of an area 1a where the data are written and an area 1b where the result of check sum is written is loaded into a processor. Thus the check sum of each data is calculated before the operation of the area 1a every time the ROM 1 is started. Then the calculated check sum is compared with the check sum of the area 1b. If one of bits of the data stored in the area 1a has a wrong change, no coincidence is obtained from the comparison of check sums. Thus the abnormality of a program stored in the ROM 1 is detected before the program starts its operation.

Description

TECHNICAL FIELD The present invention relates to a read-only memory circuit, and more particularly to a method for confirming the normality of a program written on the read-only memory circuit.

Prior Art Conventionally, in this type of program normality confirmation method, when a program is written to a read-only memory circuit (hereinafter referred to as ROM) by a ROM writer, the ROM writer automatically checks the normality of the written program. If the product is shipped after being installed in ROM or equipment,
There was no way to check the normality of the program written in the ROM in the device.

In this conventional method of checking the normality of the block diagram on RO~1, once the ROM is installed in the device and shipped, the normality of the program written in the ROM in the device is checked. Since there was no method, even if an abnormality occurred in the program on the ROM after the device was loaded, there was a drawback that the abnormality could only be detected before the program started operating.

Purpose of the Invention The present invention has been made to eliminate the drawbacks of the conventional ones as described above, and even if an abnormality occurs in the program on the ROM after the device is shipped, the abnormality is detected before the program starts operating. The object of the present invention is to provide a read-only storage circuit that can perform the following functions.

Structure of the Invention A read-only storage circuit according to the present invention includes a first storage area for storing a program running on a processing device;
and a second storage area for storing checksum results for the program stored in the storage area.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a memory map of a read-only storage circuit according to an embodiment of the present invention. In the figure, a read-only memory circuit (hereinafter referred to as ROM) 1 has a storage area 1a for storing a program for operating a central processing unit (not shown), and a storage area 1a for storing a program for operating a central processing unit (not shown). It consists of a storage area 1b for storing the results of the TUXUM.

FIG. 2 is a diagram showing an example of calculating a checksum.

Checksum calculation will be explained using FIG. 2.

“10110100′, “ttooooto”, “00
When calculating the checksum of the data “010011”, these data “10110100”, “1
1000010' and "00010011" are added bit by bit.

However, the carry generated during the addition is discarded, resulting in a checksum result of "01100101".

The operation of an embodiment of the present invention will be explained using FIG. 1 and FIG. 2.

For example, each of the above data “10110100”,
“ll000010”, “00010011” are RO
Assuming that the data is written to the MI storage area 1a, the calculation result of the Chie Tsukusum of the data "01100101" is written to the storage area 1b.

Each data “10110100”, “11000010”
, a storage area 1a in which “00010011” is written;
When a ROMI consisting of a storage area 1b in which the Chie Tsukusum result "01100101" is written is installed in a processing device (not shown) and shipped from the factory, each time a user starts up the processing device, the storage area 1b is Each data “10110100” and “11000010” written in the storage area 1a before the operation by the program 1a is started.
”.

The checksum of "ooootoott" is calculated, and the calculation result is compared with the checksum calculation result "01100i01" written in the storage area 1b.

If any bit of the data in the storage area 1a of the ROMI is erroneously changed, the comparison result will indicate a mismatch, so an abnormality in the program on the ROMI can be detected before the start of operation.

In this way, by storing the checksum calculation result of the program stored in the storage area 1a and running on the processing device in the storage area 1b, the checksum calculation result of the program stored in the storage area 1a can be calculated before the program in the storage area 1a runs. The normality of the program can be confirmed by comparing the checksum calculation result obtained when the program in storage area 1b is normal and the checksum calculation result when the program in storage area 1b is normal.
Even if an abnormality occurs in a program on M1, the abnormality can be detected before the program starts operating.

According to the present invention, as described in the detailed description of the invention,
By storing the checksum result for the program running on the processing device in the storage area provided in RO~1, even if an abnormality occurs in the program on the ROM after the device is shipped, the program will continue to work. This has the effect of being able to detect anomalies before they occur.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a memory map of a read-only storage circuit according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of calculating a checksum. Explanation of symbols of main parts 1...ROM 1a...Program storage area 1b...
・Checksum storage area Applicant: NEC Corporation (
(1 person outside)

Claims (1)

[Claims] (1) The first part stores the program that runs on the processing device.
A read-only storage circuit comprising: a storage area; and a second storage area that stores a checksum result for the program stored in the first storage area.