JPH06161795A - Method for verifying data - Google Patents

Abstract

PURPOSE:To provide a verifying method for data which can verify even fixed- length data without fruitlessness. CONSTITUTION:When data D1-D4 having substantial meaning are written in a memory, meaningless data d1-d4 which have only a digit matching function are additionally written so that the overall length becomes 30-byte fixed length. At this time, two-byte CRC check codes E1-E4 are generated for the data with the 30-byte fixed length and written together. When the written data are verified, the data d1-d4 and codes E1-E4 are read out together with the data D1-D4 and it is confirmed whether or not the respective codes are correct as to the respective data. Data whose digits are all '0' are used as d1-d4 so as to facilitate the arithmetic for generating the CRC check codes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data verification method, and more particularly to a data verification method using a CRC check code.

[0002]

2. Description of the Related Art As the degree of integration of semiconductor memories is improved,
Various information recording media are in widespread use. For example, as a new information recording medium replacing the magnetic card, recently, IC
The card is in the limelight. This IC card has a built-in memory element such as a thin RAM, ROM, or EEPROM. In such a portable information recording medium,
Very important personal data is often stored, and it is very important to verify whether a data error has occurred when reading the written data. Therefore, when writing data, it is common to add an error check code to this data. The error check code generally used in the IC card is a CRC (Cy) based on the ISO-CCITT standard.
clic Redundancy Check) Check code. For example, when writing the data D, a logical operation of a predetermined algorithm is performed on the basis of the data D to generate a CRC check code X, and the code X together with the data D is generated.
Is written in memory. Then, when reading the data D, the code X is also read together, and it is verified whether or not the code X is a correct code generated by a predetermined logical operation based on the data D. When the code X is not the correct code for the data D, it can be determined that the data D or the code X has garbled and a data error has occurred.
Usually, a verify process is performed to judge whether there is a data error by immediately reading after writing.

[0003]

When writing various data into the memory, if the data length of each data is fixed,
Convenient to handle. Especially, the E built in the IC card
Since the writing process to the EPROM is performed for each predetermined writing unit (for example, 32 bytes), the EEPROM is
If the length of the unit data to be written in is aligned with this writing unit, efficient processing becomes possible. However, in reality, it is difficult to make all the various data the same length, and the length differs for each data. As described above, in order to handle fixed-length data with different lengths, it is necessary to add extra data that has no substantial meaning. That is, when the actual data length that has a substantial meaning is less than the predetermined fixed length, by adding the extra data having the insufficient data length, the fixed length is fixed as a whole. Try to be long. However, when such extra data is added, the CRC check code is also created for this extra data. The work of performing verification by the CRC check code even on such extra data that does not have any substantial meaning is meaningless and useless, and unnecessarily prolongs the calculation time.

Therefore, it is an object of the present invention to provide a data verification method capable of performing verification without waste on fixed length data.

[0005]

According to the present invention, when writing data to a memory, a CRC check code for this data is generated, this CRC check code is written together with the data, and this data is read when reading the data. In the data verification method for checking whether or not the read CRC check code is a correct code for the read data, and a substantial meaning for the first partial data having a substantial meaning. Is added to the second partial data, and the fixed-length data is used as a writing unit so that the sum of the length of the first partial data and the length of the second partial data becomes a predetermined fixed length. The writing is performed and the second partial data is data in which all the digits are 0.

[0006]

[Operation] In the data verification method according to the present invention, data having all zeros is used as the second partial data having no substantial meaning. Originally, this second partial data is data that is meaningless to add in order to align the entire length to a fixed length, so there is no problem even if all the digits are 0. On the other hand, the CRC check code is defined as the remainder when data to be written is divided by a predetermined value. Therefore, if the data to be written includes many digits of 0, the calculation for obtaining the CRC check code can be speeded up, and the verification without unnecessary calculation can be performed.

[0007]

The present invention will be described below based on illustrated embodiments. Here, the EEP built in the IC card
The case where fixed length data is stored in the ROM will be described as an example. Now, consider a process of writing data D1 to D4 in the EEPROM of the IC card as shown in FIG. Here, the data D1 to D4 are all substantially meaningful data and have different data lengths. However, here, these data are handled as fixed length data and stored in the EEPROM. Generally, writing data to the EEPROM requires a time of the order of several ms. Therefore, the data to be written is once transferred to the write register, and the write is performed from this write register to a predetermined address of the EEPROM. Therefore, EEPRO
The writing process to M is performed for each writing unit corresponding to the data length of this writing register. For this reason, it is efficient to define a fixed length according to the writing unit to the EEPROM and save data for each fixed length.

The example shown in FIG. 1 is an example in which the writing unit (that is, the data length of the write register) to the EEPROM is 32 bytes. C according to ISO-CCITT standard
The RC check code has a length of 2 bytes. Therefore, the code area CR for this CRC check code
In order to set the length including C to 32 bytes, it is necessary to set the data area to a fixed length of 30 bytes. Therefore, the data area DATA that has a substantial meaning
In addition, the data area RFU (Reserved f
or (Future Use) is added so that the total length of the area DATA and the area RFU becomes a fixed length of 30 bytes. Specifically, data D that has substantial meaning
1 to D4 are data d1 to 1
Create a fixed-length 30-byte data by adding d4,
The CRC check codes E1 to E4 are generated for this fixed-length 30-byte data.

The CRC check codes E1 to E4 thus generated are used as data D1 to D4 (and d1 to d).
By writing together with 4), even if the data is garbled during writing, it can be detected as a data error. That is, data D1
When reading D4, meaningless data d1 to d4
Also, the CRC check codes E1 to E4 are read together, a CRC check code is generated by the same method as at the time of writing, and it is determined whether or not this CRC check code matches the read CRC check codes E1 to E4. Good. In the case of disagreement, it can be determined that data garbled data has occurred in either of them.

CRC based on the ISO-CCITT standard
As the check code, the data Q to be written is stored in a predetermined value P (specifically, "1000100000 in binary notation").
It is defined as the remainder when divided by a 17-bit number "0100001"). Therefore, for example, when writing the data D1 in FIG. 1, the value “D1 · d1” including the data d1 in the RFU area is set as the data Q, and the remainder when dividing this by the value P is The CRC check code E1 will be generated. As described above, the CRC check code E1 is generated in consideration of even the information of the data d1 which is substantially meaningless. Similarly, CRC check codes E2, E
3 and E4 are substantially meaningless data d2 and
It is generated in consideration of the information of d3 and d4. Therefore, such a CRC check code generation operation substantially includes a wasteful operation.

The present invention eliminates such useless calculation by the following method. That is, as shown in FIG. 2, substantially meaningful data (area DATA
Data with no meaning (data in the area RFU) is added to the data (marked with * in the figure) to make the total data length 3
When 0 bytes are used, data having all digits of "0" is used as data having substantially no meaning. The data in the area RFU is data added for the purpose of aligning digits so as to make the data length 30 bytes, so that any value data may be used. Therefore, data in which all digits are "0" may be used. Thus, the region R
When all the bytes in the FU are 0, the operation for generating the CRC check code becomes very simple. As described above, the CRC check code is a predetermined value P (specifically, for the entire 30-byte length data shown in FIG. 2).
"10001000000000100001" in binary notation
Is defined as the remainder at that time. Such division is actually performed in the form of a binary number, and when the dividend has 0, an operation of shifting by 1 bit on the shift register may be performed. For this reason, if the dividend includes many 0s, the operation time of this division can be shortened accordingly. Therefore, as shown in FIG. 2, adopting data in which all digits are “0” as data in the area RFU has the effect of increasing the efficiency of the operation for generating the CRC check code and reducing the operation time. Will be played. After all, according to the invention, in FIG.
The additional data d1 to d4, which have substantially no meaning, are data in which all digits are "0".

As described above, the present invention is applied to the EEPROM of the IC card.
Although the description has been made by taking the data writing to the example as an example, the present invention can be widely applied to other than the IC card.

[0013]

As described above, according to the data verification method of the present invention, in order to make the entire length a fixed length,
When adding data that does not have any substantial meaning, the data that all digits are 0 is added.
The calculation for obtaining the RC check code can be speeded up, and verification without unnecessary calculation can be performed.

[Brief description of drawings]

FIG. 1 shows four pieces of data D1 to D4, additional data d1 to d4 and CR in an EEPROM incorporated in an IC card.
It is a figure which shows the state written with C check code E1-E4.

FIG. 2 is a diagram showing a data structure in the case of storing fixed-length data according to the present invention.

[Explanation of symbols]

D1 to D4 ... Data to be written (substantially meaningful data) d1 to d4 ... Additional data for adjusting to a fixed length (substantially meaningless data) E1 to E4 ... CRC check code

Claims (1)

[Claims] 1. When writing data to a memory, a CRC check code for this data is generated, and this CRC check code is written together with the data. When reading the data, this data is read out and read out together with the CRC check code. In the data verification method for checking whether or not the CRC check code is a correct code for the read data, the first part having substantially meaning, the second part having substantially no meaning for the data. Data is added so that the sum of the length of the first partial data and the length of the second partial data becomes a predetermined fixed length, and writing is performed using the fixed-length data as a writing unit, and A data verification method, wherein data having all digits of 0 is used as the second partial data.