JPH04284556A - Microcomputer - Google Patents

Abstract

PURPOSE:To hold the secret of contents in a memory by outputting data read out of the memory while arbitrarily exchanging the bits of the data so that the third personnot knowing which bit is exchanged can not know the correct data. CONSTITUTION:Under the control of a CPU 1, the content output start address of a ROM 3 is set to a program counter 4, and this address is outputted from the counter 4 to the ROM 3. A ROM data corresponding to this address is outputted from the ROM 3 to a data bus 6 and inputted to a bit switching circuit 7. At the circuit 7, the bits are exchanged, and the result is outputted to an input/output port 5. Afterwards, the counter 4 increases or decreases the contents, the data in the ROM 3 are successively outputted to the circuit 7 and at the circuit 7, the inputted data in the ROM 3 are successively outputted to the input/output port 5 while exchanging the bits.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer with a built-in ROM, and more particularly to keeping the contents of the ROM confidential.

0002

2. Description of the Related Art FIG. 2 is a block diagram showing the structure of a conventional one-chip microcomputer. In Figure 2,
1 is a CPU (central processing unit) that performs calculations and controls necessary for data processing, 2 is a RAM that temporarily stores data necessary for data processing, and 3 stores data necessary for CPU 1 to operate. ROM, 4 is RAM2 and ROM3
5 is an input/output port for inputting and outputting data, and 6 is a data bus connecting each of the above components.

Next, the operation will be explained. In order to check the contents (data) of ROM3, CPU1
When outputting the contents of ROM 3 from the input/output port 5, first, the contents output start address of the ROM 3 is set in the program counter 4, and this address is output from the program counter 4 to the ROM 3. ROM data corresponding to this address is output from the ROM 3 to the data bus 6, and ROM data is output from the input/output port 5 via the data bus 6. Thereafter, the program counter 4 increments or decrements its contents and outputs the address to the ROM 3. Therefore, the CPU 1 sequentially outputs the contents of the ROM 3 corresponding to the address from the input/output port 5.

0004

[Problem to be solved by the invention] Since the conventional one-chip microcomputer is configured as described above,
The contents of the ROM are read directly from the input/output port,
This poses a problem in terms of confidentiality in that a third party can easily learn the contents of the ROM.

[0005] This invention was made in order to solve the above-mentioned problems, and its purpose is to provide a one-chip microcomputer in which the contents of the memory cannot be easily known to a third party even if the contents are read out. shall be.

[0006]

[Means for Solving the Problems] A microcomputer according to the present invention includes a bit switching circuit 7 that arbitrarily switches and outputs bits of data read out from a memory (ROM 3) by a central processing unit (CPU 1). It is something.

[0007]

[Operation] The bit switching circuit 7 is connected to the central processing unit (CPU1).
), the bits of the data read from the memory (ROM3) are arbitrarily replaced and output.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the structure of a one-chip microcomputer according to an embodiment of the present invention. In FIG. 1, components corresponding to those shown in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. In FIG. 1, reference numeral 7 denotes a bit switching circuit that arbitrarily switches bits of data read out from the ROM 3 by the CPU 1 and outputs the same.

Next, the operation when checking the contents of the ROM in this embodiment will be explained. First, the CPU
1, the content output start address of the ROM 3 is set in the program counter 4, and this address is output from the program counter 4 to the ROM 3. ROM
3 outputs the ROM data corresponding to this address to the data bus 6, and inputs it to the bit switching circuit 7 via the data bus 6. Bit switching circuit 7 performs bit switching, and the result is output to input/output port 5. Thereafter, the program counter 4 increments or decrements its contents and sequentially outputs the data (contents) of the ROM 3 to the bit switching circuit 7. The bit switching circuit 7 switches the bits of the input data in the ROM 3 and sequentially outputs the data to the input/output port 5.

[0010] In the above embodiment, the data in the ROM passes through the data bus when entering the bit switching circuit.
It is also possible to enter the bit switching circuit directly from the ROM, or
Although the output from the bit switching circuit was directly output to the input/output port, it may also be output via a data bus. The bit switching circuit may have any configuration as long as it can select the bit to be replaced. In addition, the selection method of the bit to be replaced is selection by aluminum wiring,
Selection using a depletion transistor may be considered, but there is no restriction on the selection method.

[0011]

As described above, according to the present invention, since the bit switching circuit is provided to arbitrarily switch and output the bits of data read from the memory, the memory data with the bits switched can be changed, for example. This is output from the input/output port, and users who know which bits have been swapped can check the memory contents, but third parties who do not know which bits have been swapped can check the correct address. The memory data cannot be known, so the effect is that the memory contents can be kept confidential.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a one-chip microcomputer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a conventional one-chip microcomputer.

[Explanation of symbols]

1 CPU (Central Processing Unit) 3 ROM (memory) 7 Bit switching circuit

Claims (1)

[Claims] Claim 1: A microcomputer comprising a central processing unit that performs calculations and controls necessary for data processing, and a memory that stores data necessary for the central processing unit to operate, wherein the central processing unit A microcomputer comprising a bit switching circuit that arbitrarily switches bits of data read from the memory and outputs the same.