JPH0455961A - Microcomputer - Google Patents

Abstract

PURPOSE:To prevent the illegal read of a program by inhibiting the reading operation of a reading circuit in accordance with the contents of a read control information storage area allocated to a partial area of a programmable ROM. CONSTITUTION:A read inhibiting circuit 30 consists of eight 2-input AND gates 30a - 30h having such configurations where the program data DR0 - DR7 outputted from a programmable ROM 21 are applied to one of both input terminals together with the 1-bit information received from a read control information storage area 21b applied to the other input terminal respectively. Therefore the data DR0 - DR7 can be transmitted with the 1-bit information of the area 21b is equal to '1'. Then the transmission of these program data is inhibited when the 1-bit information is equal to '0' respectively. Thus it is possible to prevent the illegal read of a program by writing the information '0' into the area 21b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microcomputer having a programmable ROM (read only memory).

[Prior Art] Generally, microcomputers use R for program storage.
It has a built-in OM.

If this ROM is a mask ROM, the program is set in the process of manufacturing the microcomputer. For this reason, it takes a long time from the time a software engineer creates a program until the time when a microcomputer with a built-in mask ROM in which this program is set is manufactured.

In addition, in the case of microcomputers that are used in small quantities,
Since it is necessary to create a different mask for each type, problems arise in terms of labor and cost.

In order to solve these problems, microcomputers have been developed that include a programmable ROM into which programs can be electrically written after the microcomputer is created.

FROM (Programmable ROM) is different from EFROM (Erasable Programmable ROM) due to the difference in the element structure that constitutes it.
ROM), E2PROM (electrically erasable FR
OM) and non-volatile PROM.

In EPROM, electrically written data is erased all at once by irradiation with ultraviolet light.

E2FROMs are divided into two types, depending on the method of erasing data: a 1-bit rewritable type in which each bit is rewritten, and a flash type in which all data or blocks are erased. This flash type E2FROM has a short erasing time.
It has the advantage of being cheaper to manufacture than the 1-bit rewritable type, and is becoming the mainstream of E2FROM.

Non-volatile FROM has a structure in which data written electrically cannot be erased, and fuse blowing type FROM
There are M and diode destruction type FROM.

FIG. 3 is a block diagram schematically showing the configuration of a conventional microcomputer incorporating a programmable ROM as described above.

In the figure, lO indicates a microcomputer, and this microcomputer 1θ includes a programmable ROM II, a program counter I2, an ALU (arithmetic unit) 13, a register 14, a RAM (random access memory) 15, a peripheral circuit 16, and Input/output boat 17
etc. are provided.

The created program is written to the programmable ROM II through the input/output port 17. In order to check whether the program has been written correctly, a function is provided to read data from the programmable ROM II to the outside. This function is called a read function.

FIG. 4 shows a circuit for writing and reading a program to the programmable ROM II in the microcomputer 10.

The program write operation is started by externally setting the microcomputer IO to write mode. In this write mode, program address A. -A
7 is applied to the input/output port 17, the address decoder 18 selects a 1-byte memory cell in the memory matrix of the programmable ROM II. At this time, the write signal is externally sent to the programmable ROMI.
When given to I, program data D is input to the input/output port 17. ~D7 and the same data Dvo-Dv7 are written into the above-mentioned selected 1-byte memory cell. Writing is completed by writing the program in this procedure for all addresses.

The program read operation is carried out by the microcomputer l.
Read address A with O set to read mode. -A. is applied to the input/output port 17. As a result, the program data at the corresponding address in the memory matrix D RO-D R? is output, and is output to the outside via the input/output port 17.

[Problem to be solved by the invention] According to the conventional microcomputer as described above,
There is a risk that the program in the programmable ROM may be read out illegally by using the read function.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a microcomputer in which programs written in a programmable ROM cannot be read out illegally.

[Means for Solving the Problems] The gist of the first invention of the present application which achieves the above-mentioned object is to provide a programmable ROM into which a program is written, a reading circuit for reading the program in the programmable ROM, and a part of the programmable ROM. The present invention includes a read control information storage area assigned to the subarea, and a read blocking circuit that blocks the read operation of the above-mentioned read circuit according to the contents of the read control information storage area.

A second gist of the invention of the present application is a programmable ROM into which a program is written, a readout circuit for reading out the program in the programmable ROM, and an area allocated to a partial area of the programmable ROM arranged adjacent to the programmable ROM. The present invention is provided with a readout control information storage area, and a readout prevention circuit that blocks the readout operation of the readout circuit according to the contents of the readout control information storage area.

The gist of the third invention of the present application further includes the above-mentioned partial areas.
A function change control information storage area is allocated to store information for changing the function of the microcomputer.

[A read control information storage area allocated to a partial area of the programmable ROM where the action co-program is written or a read control information storage area allocated to a partial area of the programmable ROM located adjacent to the programmable ROM where the program is written. The read operation of the read circuit is controlled by the information written in the area, and the program cannot be read after writing the information that prohibits the read operation.

[Example code] Examples of the present invention will be described in detail below.

FIG. 1 is a block diagram schematically showing the configuration of an embodiment of the present invention.

In the figure, 20 indicates a microcomputer, and the microcomputer 20 includes a programmable ROM 2, a program counter 22, an ALU 23, a register 24, a RAM 25, a peripheral circuit 26, an input/output port 27, an address decoder 28, and a programmable ROM 2. Buses 29 and the like that connect to each other are provided in a normal connection form.

In this embodiment, a read blocking circuit 30 is further provided in a reading circuit for a program read from the programmable ROM 21.

In this embodiment, an EPROM (erasable memory) is used as the programmable ROM 21 for storing programs.
ROM) is used, and this programmable ROM
A partial area (1 byte) of 21 includes a function change control information storage area 21a for controlling some of the functions of the microcomputer 20 and a read control information storage area 21b for controlling reading of the program to the outside. is formed.

The function change control information storage area 21a is connected to a function change section (not shown), and stores information for changing some functions of the microcomputer 20 according to the intended use. For example, the function to set an input/output port as an input-only port or an output-only port, the function to set the internal resistor attached to an input port to be a pull-up resistor or a pull-down resistor, or the polarity of the input or output signal level. This is a function to change the Of course, the function may be changed to other functions.

The read control information storage area 21b is the read block circuit 3
0, and 1-bit information for controlling the read blocking circuit 30 is written therein.

In this embodiment, as shown in FIG. 1, the program data is 8 bits and the program address is (m+1) bits. However, the present invention can be similarly implemented with other bit numbers. Alternatively, program address selection may be performed serially using one bit.

FIG. 2 is a circuit diagram showing a configuration example of the read blocking circuit 30 shown in FIG. 1.

As shown in the figure, the read blocking circuit 30 stores program data DRO output from the programmable ROM2+.
~DR7 is applied to one input terminal, and 1-bit information from the read control information storage area 21b is applied to the other input terminal. has been done. Therefore, when the 1-bit information from the read control information storage area 21b is "1", the program data DRO-'-
If D R7 is enabled to pass and is "0", the program data D. - Passage of DR7 is blocked.

The configuration of this read blocking circuit 30 is not limited to the example shown in FIG. 2, and may be of any configuration as long as it can block passage of program data according to information from the read control information storage area 21b. .

Next, the operation of this embodiment will be explained.

The program writing operation is started by setting the microcomputer 20 to a writing mode from the outside. In this write mode, the program address A applied to the input/output port 27. ~A, is applied to address decoder 28 via bus 29. The address decoder 28 selects one byte of memory cell in the memory matrix of the programmable ROM 21. At this time, when a write signal is applied to the programmable ROM 21 from the outside, program data D is input to the input/output port 21. -Data D, same as D7. ~
D,7 is written into the selected 1-byte memory cell mentioned above. Writing is completed by writing the program in this procedure for all addresses.

Programmable ROM21 to check the program
When reading a program from , it operates as follows.

First, the initial state of the read control information storage area 21b is set to "
Set it to 1. This state is programmable ROM2+
This corresponds to a state in which the data has been initialized by erasure of ultraviolet rays.

In this state, the microcomputer 20 is set to read mode and the read address A is set. -A, is applied to the input/output port 27, program data D, of the corresponding address is output from the memory matrix. ~D, 7 is output. Since the 1-bit information from the read control information storage area 21b is "1", the read blocking circuit 30 detects the program data D! 10-'-D l? Therefore, the same data D+to' to D117' as the program data D10 to DR7 are outputted to the outside via the input/output port 27.

In this way, during the period when the information in the read control information storage area 21b is "1", the program written in the programmable ROM 21 can be read out to the outside and checked.

After this verification is completed, the read control information storage area 21
Write information “0” to b. As a result, the read blocking circuit 30 enters a state of blocking the passage of the program data Dio-D117. As a result, even if accessed from outside the microcomputer 20, the programmable ROR
The program stored in 21 is not output from the input/output port 27.

Once information of "0" is written in the read control information storage area 21b, the program cannot be read from now on. That is, in an attempt to put the read blocking circuit 30 into a state where program data can pass, the read control information storage area 21
In order to return the information b to "1", the programmable ROM 21, which is an EFROM, must be irradiated with ultraviolet light. However, when the programmable ROM 2+ is irradiated with ultraviolet rays, the stored programs themselves are all erased, so that the programs cannot be read after all.

In this embodiment, a programmable ROR for program storage is used.
Since the function change control information storage area 21a and the read control information storage area 21b are formed in a partial area (1 byte) of the programmable ROM 21, the address line of the programmable ROM 21 can be shared. Therefore, programmable ROM21
Function change control information storage area 2 is written at the same time as the program is written using a FROM writer corresponding to the memory capacity of
1a and the read control information storage area 21b, it is possible to easily change functions and control program calls.

Note that the read control information storage area may be provided in an EFROM separate from the program storage EFROM built into the same microcomputer.

In this case, both EFROMs are placed adjacent to each other during layout design. As a result, all stored programs will be erased when UV rays are irradiated.
Unable to read program.

In the above embodiment, EPRO is used as a programmable ROM.
Although M is used, a flash type E2FROM may also be used, and the effects will be the same in that case. That is, in order to change the information in the read control information storage area 21b and read the program, it is necessary to erase the information in block units or all the information, so the program is also erased and it becomes impossible to read the program. Become.

A nonvolatile FROM may be used as the programmable ROM, and the effects in that case are also the same. That is, if the information in the read control information storage area 21b is changed after reading and verifying the written program, it will no longer be possible to read the program.

[Effects of the Invention] As explained in detail above, according to the present invention, there is provided a programmable ROM into which a program is written, a readout circuit for reading out the program in the programmable ROM, and an area allocated to a part of the programmable ROM. A read control information storage area allocated to the read control information storage area or a partial area of the programmable ROM arranged adjacent to the programmable ROM in which the program is written, and the above-mentioned reading 6 according to the contents of the read control information storage area. Since the device is equipped with a read blocking circuit that blocks the read operation of the read circuit, unauthorized reading of the program can be prevented by changing the information in the read control information storage area after reading and verifying the program.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of the read blocking circuit shown in FIG. 1, and FIG. 3 is a block diagram showing the configuration of a conventional microcomputer. FIG. 4 is a block diagram schematically showing a circuit for writing a program into the programmable ROM of FIG. 3 and a circuit for reading the program. 20...Microcomputer, 21...
...Programmable ROM, 21a... Function change control information storage area, 21b... Read control information storage area, 22... Program counter,
23...ALU, 24...Register,
25...RAM, 26...peripheral circuit,
27...Input/output port, 28...Address decoder, 29...Bus, 30...
- Read blocking circuit, 30a to 30h...AND gate.

Claims (3)

[Claims] (1) Programmable ROM into which programs are written
and a readout circuit for reading out a program in the programmable ROM, the microcomputer having a readout control information storage area allocated to a partial area of the programmable ROM, and a readout control information storage area according to the contents of the readout control information storage area. and a read blocking circuit for blocking a read operation of the read circuit. (2) Programmable ROM into which programs are written
and a readout circuit for reading out a program in the programmable ROM, the readout control information storage area allocated to a partial area of the programmable ROM arranged adjacent to the programmable ROM; A microcomputer comprising: a read blocking circuit that blocks a read operation of the read circuit according to the contents of a read control information storage area. (3) The microcomputer according to claim 1 or 2, wherein a function change control information storage area for storing information for changing the function of the microcomputer is further allocated to the partial area. .