JPH05204765A - Microcomputer - Google Patents

Abstract

PURPOSE:To prevent data stored in an external storage device from being read by the third person in the microcomputer provided with the external storage device. CONSTITUTION:By integrating a code deciphering circuit 1 and a keyword circuit 2 into a main body 3 of the microcomputer, data outputted from an external storage device 4 are converted by the code deciphering circuit 1 and outputted to an internal data bus 7. The code deciphering circuit 1 can design the circuit by using arbitrary signals in the main body of the microcomputer, and this time, the code deciphering circuit 1 is constituted by using the low-order 8 bits of an address bus 5 and the key-word circuit 2. Therefore, by storing ciphered data in the external storage device 4 beforehand, the data stored in the external storage device 4 can be prevented from being read by the third person.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer, and more particularly to a microcomputer incorporated in various electric devices such as personal computers, consumer products and industrial products.

[0002]

2. Description of the Related Art Generally, microcomputers are used in a wide range of fields regardless of whether they are for consumer use or industrial use, and are also used for consumer and industrial controllers for computers and robots. It is used as a device.

An example of a conventional microcomputer is shown in FIG.

FIG. 3 shows a Maokuro computer main body 3 and an external storage device 4 for storing instructions and data for operating the microcomputer main body 3. The microcomputer body 3 and the external storage device 4 include a data bus 13 for reading data in the external storage device 4 and an address bus for designating which part of the external storage device 4 to read data. 5 and a read signal 8 that specifies the timing of reading data from the external storage device 4.

[0005]

In the conventional microcomputer, as shown in FIG. 3, the external storage device 4 is used.
Since the microcomputer 3 and the microcomputer main body 3 are directly connected by the data bus 13, there is a risk that a third party may read the data stored in the external storage device 4.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above drawbacks and provide a microcomputer which prevents a third party from reading the contents stored in the external storage device.

[0007]

The structure of a microcomputer of the present invention is a microcomputer in which a microcomputer main body and an external storage device are connected by a data bus, and the external storage device and the microcomputer main body are connected to each other. An intervening decryption circuit and a key word circuit are provided in between, and the decryption circuit and the key word circuit are incorporated into the inside of the microcomputer body.

[0008]

1 is a block diagram showing a microcomputer according to an embodiment of the present invention.

In FIG. 1, the microcomputer of the present embodiment is capable of taking in an arbitrary internal signal of the microcomputer main body 3 and having an internal circuit freely designed, and the decrypting circuit 1. , A microcomputer main body 3 including the decryption circuit 1 and the key word circuit 2, an external storage device 4 for storing instructions and data for operating the microcomputer main body 3, and an external device. An address bus 5 having a bus width of 16 bits for the microcomputer body 3 to specify which part of the memory device 4 to read data, and data in the external storage device 4 is read into the microcomputer body 3 and decrypted. The 8-bit external data bus 6 for input to the circuit 1 and the data decrypted by the decryption circuit 1 An 8-bit internal data bus 7 for use inside the microcomputer body 3, a line of a read signal 8 for designating a timing of reading data from the external storage device 4, a key word circuit 2 and a decryption circuit 1. And an 8-bit data bus 9 for connecting the.

The decryption circuit 1 in FIG. 1 is originally a circuit that can be freely designed by a third party, but in this embodiment, the lower 8 bits of data and the key
It is composed of the output data of the word circuit.

The key word circuit 2 is composed of an 8-bit non-volatile memory, and its contents can be rewritten from outside the microcomputer body 3 at any time. In the present embodiment, the contents of the key word circuit 2 are hexadecimal 3F.
Is stored.

Next, details of the decryption circuit 1 in FIG. 1 will be described with reference to FIG.

In FIG. 2, the address bus 5, the external data bus 6, the internal data bus 7, and the data read signal 8 are the same as those in FIG.

In FIG. 2, the decryption circuit 1 and the key
The word circuit 2 is shown, and the decryption circuit 1 takes the exclusive OR of the data bus 8 and the external data bus 6 and outputs the value to the data bus 12. And an exclusive OR circuit 11 that takes the exclusive OR of the data bus 12 and the address bus 5 and outputs the value to the data bus 7.

Next, the operation of the microcomputer of this embodiment will be described with reference to the drawings.

In FIG. 1, consider a case where the microcomputer main body 3 reads 8-bit data stored in the hexadecimal address [1234] from the external storage device 4. Next, it is assumed that the address [1234] (hexadecimal) of the external storage device 4 stores [75] in hexadecimal.

First, the microcomputer main body 3 outputs address data [1234] in hexadecimal to the address bus 5, and then the microcomputer main body 3 outputs a read signal 8. When the read signal 8 is input, the external storage device 4 outputs the data [75] (hexadecimal) of the area designated by the address bus 5 to the external data bus 6.

The decryption circuit 1 carries out an exclusive OR of the data of the lower 8 bits of the external data bus 6 and the address bus 5 and the data of the key word circuit 2 sent via the data bus 9. And output the value [7E] to the internal data bus 7.

As can be seen from the above description, the data to be stored in the external storage device 4 includes the data originally required for the microcomputer main body 3, the lower 8 bits of the address to be stored in the external storage device 4, and the key word. It is understood that it is sufficient to store the data obtained by taking the exclusive OR of both the 8-bit data stored in the circuit 2.

In this case, since the data stored in the external storage device 4 is different from the original data, nobody other than the microcomputer designer can understand the data.

[0021]

As is apparent from the above description, according to the microcomputer of the present invention, it is possible to obtain the effect that the data stored in the external storage device cannot be read by a third party.

[Brief description of drawings]

FIG. 1 is a block diagram of a microcomputer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing details of a decryption device included in a microcomputer according to an embodiment of the present invention.

FIG. 3 is a block diagram of a microcomputer as a conventional example.

[Explanation of symbols]

 1 Decryption Circuit 2 Key Word Circuit 3 Microcomputer 4 External Storage Device 5 Address Bus 6 External Data Bus 7 Internal Data Bus 8 Data Read Signal 10, 11 Exclusive-OR Circuit 12, 13 Data Bus

Claims (1)

[Claims] 1. A microcomputer in which a microcomputer main body and an external storage device are connected by a data bus, and a decryption circuit and a key word circuit are provided between the external storage device and the microcomputer main body. A microcomputer characterized in that the encryption / decryption circuit and the key / word circuit are incorporated in the microcomputer body.