JPH03278151A - Semiconductor storage device - Google Patents

Abstract

PURPOSE:To eliminate the need of a peripheral equipment for preventing read- out by providing a switch for storing a programmable cipher code for deciding whether read-out of storage data is appropriate or not. CONSTITUTION:In the case of executing read-out, when a read-out application input code signal is inputted from an address bus 9, and also, this input code signal is latched to a latch circuit 7 by controlling a latch control 8, a compara tor 5 compares it with a cipher code stored in a mask ROM 3 output through a cipher code bus 4. When both of the coincide with each other, a switch control 10 is activated, a switch circuit 11 is made in an ON-state, and address informa tion of the address bus 9 is transferred to a main memory 13. In the case the input code signal and the cipher do not coincide with each other, the switch circuit 11 remains cut-off, and by an address signal, storage data of a main memory 13 is not output normally. In such a way, a peripheral equipment for preventing read-out becomes unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor memory device, and particularly to the configuration of a peripheral circuit.

[Conventional technology]

Conventionally, in this type of semiconductor memory device, stored information can be easily read by setting a control terminal to a read mode and inputting address information.

[Problem to be solved by the invention]

In the semiconductor memory device described above, the stored information can be easily read, and the stored information can be easily used by a third party. Therefore, if it is necessary to prevent reading by a third party, it is necessary to install a peripheral device to prevent reading so that stored information cannot be read from the semiconductor device, and this requires a large amount of effort. The disadvantage is that it is costly and time consuming.

[Means to solve the problem]

The semiconductor storage device of the present invention includes, in addition to the main memory, a nonvolatile memory for storing a read encryption code, and a circuit that compares the input code and the encryption code and transmits address data to the main memory only when the two match. have.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

The semiconductor memory device according to the present invention includes a main memory 13, a nonvolatile memory 3 for storing an encryption code, and a latch circuit 7.
, a comparator 5 that compares the input code and the encryption code, and a switch circuit 1 that connects or disconnects the address bus 9.
Consisting of 1.

When reading, a read request manual code signal is input from the address bus 9, and the latch control 8 is controlled to latch this input code signal into the latch circuit r. The code stored in the mask ROM 3 is compared with the encoded code output from the mask ROM 3, and if the two match, the switch control 10
is activated, the switch circuit 11 is made conductive, and the address information on the address bus 9 is transmitted to the main memory 13.

It is obvious that if the input code signal and the code do not match, the switch circuit 11 remains cut off, and the address signal does not normally output the data stored in the main memory 13.

When reading out the main memory 13, the stored contents of the main memory 13 are read by inputting the address information to the address bus 9 and the control signal to the control bus 15 while the input code signal is latched by the latch circuit 7. Output from data bus 14.

In this embodiment, a mask ROM is used as the nonvolatile memory 3, and especially when the main memory 8 is a mask ROM, R
A semiconductor memory device according to the present invention can be obtained by ordering an OM code and a read encryption code from a semiconductor manufacturer.

[Example 2] FIG. 2 is a block diagram of a second embodiment of the present invention.

In this embodiment, an EEP'ROM is used as the nonvolatile memory 3, and the encryption code can be changed at any time.

To change the encryption code, first control the switching control 18 to select the nonvolatile memory/main memory switching circuit 16 to the nonvolatile memory side, and then input the same signal as the previously registered encryption code from the address bus 9. After making the switch circuit 11 conductive, the write control 19 is controlled while inputting a new encryption code from the address bus 9 to the nonvolatile memory 3 via the new encryption code F bus 17. The process ends by writing to the EEPROM of the non-volatile memory 3. After the writing is completed, a new encryption code is output from the encryption code bus 4, so the comparator 5 only accepts the new encryption code.

In this embodiment, since an EEPROM is used as the nonvolatile memory 3, there is an advantage that the encryption code can be changed on the board at any time.

〔Effect of the invention〕

As explained above, the present invention allows the semiconductor storage device itself to be easily protected from reading by a third party, so there is no need to provide a peripheral device to prevent reading in the device design, and cost and time can be reduced. Furthermore, it has the effect of reducing the cost and time required to encrypt the stored information itself. Furthermore, by allowing the read prevention code to be changed at any time as in the second embodiment, leakage and theft of information can be prevented as much as possible, which has the effect of ensuring sufficient airtight protection.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a block diagram of a second embodiment. 577 1...Operating power supply terminal, 2...GND,
3...Nonvolatile memory, 4...Encryption code bus, 5...Comparator, 6...Input code bus, 7...・Latch circuit, 8...
...Latch control, 9...Address...
Bus, 10...Switch control, 11
...Switch circuit, 12...Internal address bus, 13...Main memory, 14...
...Data bus, 15...Control bus, 16...Nonvolatile memory/main memory switching circuit, 17...New encryption code bus, 18.
...Switching/control, 19...
light control.

Claims (1)

[Claims] A semiconductor storage device that includes a switch that stores a programmable cryptographic code that determines whether or not stored data can be read.