JPS63108600A - Semiconductor device - Google Patents

Abstract

PURPOSE:To maintain the information secret of a read only memory by comparing the information read from the read only memory with externally supplied information and storing and externally outputting the compared result after all the read information is compared. CONSTITUTION:The storing information of a designated address is outputted to a data bus 3 based on address information supplied from an address bus 2 by a ROM1 requiring an inspection. When an address counter 4 counts the number of pulses supplied externally, supplies it to the bus 2 and the counting of a size of the ROM1 is completed, a count completion signal is transmitted to an output control circuit 5. A comparator 6 compares the information read to the bus 3 from the ROM1 with the externally supplied information EX to set a discordance flag 7 and when the circuit 5 receives the count completion signal from the counter 4, it outputs the contents of the flag 7 externally. In such a way, the information secret of the ROM1 is maintained and the suitability of the information stored in the ROM1 can be externally discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor device, and particularly to a semiconductor device incorporating a read-only memory (hereinafter referred to as ROM).

[Prior Art] Conventionally, as this type of semiconductor device, the semiconductor device μC0M-84 manufactured by NEC Corporation is known, and this semiconductor device μC0M-84 stores a program in a built-in ROM. . The procedure for reading out the program stored in this ROM will be explained based on FIGS. 4 and 5.
First, when a predetermined positive voltage is applied to the EA terminal, the semiconductor device enters the internal ROM read mode, and when the ROM address is supplied to terminals P20 to P22 while the RESET (bar) signal is "0", the RESET (bar) The ROM address is latched internally at the rising timing (T) of . Thereafter, the information stored in the ROM address supplied while RESET (bar) is "1" is output to the data terminals DBO to DB7.

Therefore, the information stored in the built-in ROM is once read out to the outside using the above procedure, and then compared with the expected value to determine its suitability.[Problem to be Solved by the Invention] However, In the case of conventional semiconductor devices, as mentioned above, there was a function to read out the information stored in the ROM, so if important information is stored in the ROM, the information cannot be accessed by another person. There was a problem that the data could be read out and the secret could not be maintained.

It is therefore an object of the present invention to provide a semiconductor device in which the suitability of information stored in a ROM can be determined, but the contents are not made known to others.

[Means, Actions, and Effects for Solving the Problems] A semiconductor device according to the present invention is a semiconductor device in which an integrated circuit including a read-only memory is formed on a semiconductor substrate, in which the integrated circuit is sequentially read out from the ROM. a comparison means for comparing the information with information supplied from the outside; a storage means for temporarily storing the results compared by the comparison means;
The apparatus is characterized by comprising an output means for outputting the comparison result from the storage means to the outside after all the information read from the read-only memory is compared.

The semiconductor device according to the above configuration sequentially reads information from the ROM and compares the information read from the ROM with information supplied from the outside by the comparing means.

The comparison results for the above information are temporarily stored in the storage means, and after the comparison of all information is completed, the comparison results are sent to the outside. Therefore, although the contents of the information stored in the ROM cannot be known from the outside, it is possible to know whether the information stored in the ROM matches external information, and it is possible to know whether the information stored in the ROM matches external information. Necessary tests can be performed while keeping the information confidential.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. In the figure, 1 is a ROM that requires inspection, and this ROM 1 outputs the information stored at the address specified by the address information to the data bus 3 based on the address information supplied from the address bus 2. . The address counter 4 counts the number of pulses supplied from the outside and supplies the counted value to the address bus 2. When the address counter 4 completes counting for the size of the ROM 1, an output control circuit 5 outputs a count end signal. Send to. A comparator 6 as a comparison means compares the information read from the ROM 1 to the data bus 3 with the information IE3EX supplied from the outside, and if the comparison result does not match, sets a mismatch flag 7 as a storage means. . When the output control circuit 5 receives the count end signal from the address counter 4, it outputs the contents of the mismatch flag 7 to the outside. Therefore, when testing the information stored in the ROM 1, the semiconductor device having the output control circuit 5, the comparator 6, and the discrepancy flag 7 can be accessed from the ROM 1 by supplying a pulse from the outside and incrementing the address counter 4. The comparator 6 converts the information read out sequentially into normal information EX supplied from the outside.
When a mismatch is found between the information read from the ROM 1 and the information EX supplied from the outside, the mismatch flag 7 is set, and when they match, the mismatch flag 7 is not set. The state of this mismatch flag 7 is read out in response to the count end signal, so the ROM 1
Although the suitability of the information stored in the computer can be determined externally, the content of the information cannot be determined.

FIG. 2 is a block diagram showing the configuration of a second embodiment of the present invention, and this second embodiment shows the case where the present invention is applied to a microcomputer device incorporating a ROM 10.

In the second embodiment, information is sequentially read from the ROM 10 according to the flowchart in FIG.
In step 100), the information corresponding to the read information is stored in the accumulator of the input/output control circuit 9.
(Step 101), and the read information is subtracted from the information stored in the accumulator (Step 102). If the result is other than 0, set the mismatch flag (step 103); if the result is 0, do not set it. When all the information in the ROM 10 is compared in this way, only the state of the mismatch flag is sent to the outside (step 10).
4). In the case of the second embodiment, since the central processing unit 8 is used, there is an advantage that the amount of additional hardware is small. The step 102 realizes a comparison means, the step 103 realizes a storage means, and the step 104 realizes an output means.

As explained above, in each embodiment of the present invention, information in the ROM is compared with normal information and only the result is output, so that the information stored in the ROM is not known to others.

For example, suppose the ROM stores 1000 bits of information, and the time required to check all bits once is 100 bits.
If it is μsec, it is impossible to determine whether the input data is correct or not unless all bits are checked, so the average time required to know the contents is 218"" x 100 μs e c Xi/2 = 3 x 1028 ( , 2000), and it is impossible for others to realistically know the contents of the ROM.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention. Flowchart diagram, Figure 4 is a block diagram showing a conventional example, and Figure 5 is a timing diagram of a conventional example.61.10...
ROM, 2..◆◆..address bus, 3..data bus, 5..output means (output control circuit), 6・
...Comparison means (comparator), 7...
...Storage means (mismatch flag), 8...
... Central processing unit, 9... Human output control circuit. Patent Applicant NEC Corporation Agent Patent Attorney Kiyoshi Kuwai Hiss Figure 1 Figure 2

Claims (1)

[Scope of Claims] A semiconductor device in which an integrated circuit including a read-only memory is formed on a semiconductor substrate, comprising: comparing means for comparing information sequentially read out from the ROM by the integrated circuit with information supplied from the outside; It has a storage means for temporarily storing the results compared by the comparison means, and an output means for outputting the comparison results from the storage means to the outside after all the information read from the read-only memory has been compared. A semiconductor device characterized by: