JPH01245345A - Single chip microcomputer - Google Patents

Abstract

PURPOSE:To prevent a program from being illegally copied by a third person by writing data for inhibiting the reading of data written in a P-ROM in a register for controlling the reading. CONSTITUTION:A program is written in a prescribed address of the P-ROM 8 by means of a P-ROM writer through a write control circuit 7 and an internal data bus 11 at first, and then read out again through the bus 11 and a read control circuit 6 to check the data. Then information for inhibiting the reading of data stored in the ROM 8 is written in a register 9 through the circuit 7 and the bus 11. Even if a third person intends to read out the program by means of a P-ROM writer, a read inhibiting signal 10 written in the register 9 inhibits the reading operation of the circuit 6 and the reading of data from the ROM 8 is suppressed because data for inhibiting the reading of data written in the ROM 8 is written in the register 9.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a single-chip microcomputer with a built-in read-only memory (PROM), and particularly to a PR
This invention relates to an OM readout control circuit.

[Conventional technology]

Conventionally, this type of single-chip microcomputer has an address input terminal 2 for specifying an arbitrary address of the P'ROM 8, as shown in FIG. A circuit 7 is connected to PROM8. Furthermore, a CPU 12, RAMI 3, and other control circuits 14 are connected to the internal data bus 11. The read control circuit 6 and the write control circuit 7 are connected to data input/output terminals Do to D7 via a common data bus 3, and the read control circuit 6 receives a read control signal input from the read control signal input terminal 5. The write control circuit 7 is controlled by a write control signal input from the write control signal input terminal 4.

Next, to explain the operation of this single-chip microcomputer, when writing a predetermined program to PROMB, input an address signal from address input terminal 2 to specify an arbitrary address in PROM 8, and use the write control signal to write the program. The control circuit 7 is energized and predetermined data is written to the designated address via the data bus 3 and the internal data bus 11. Also, when reading, an arbitrary address is specified, the read control circuit 6 is activated by the read control signal, and the data to be read is output to the data input/output terminals D0 to D via the internal data bus 11 and the data bus 3. , was checking the written data.

[Problem to be solved by the invention]

The above-described conventional read control circuit has the drawback that data in the built-in PROM can be easily read by a third party using a commercially available PROM writer, and the program can be illegally copied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a single-chip microcomputer that prohibits reading data from a built-in PROM to the outside.

[Means to solve the problem]

The single chip microcomputer of the present invention is
It has a PROM-structured register that specifies permission or prohibition of reading data from the built-in PROM to the outside, and a read control circuit that controls reading of the data from the built-in PROM based on the contents of the register. .

〔Example〕

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

An embodiment of the present invention will be explained with reference to FIG.

The capacity of PROMg is 16K (214) bytes, and the address input terminal 2 is 15 bits. The register 9 that controls reading is given an address set in addition to the PROM 8, and is written using the same writing method as the PROM 8. In other words, if byte 16 of PROM 8 is a memory area used by the user, then register 9 of the PROM structure to which an address additionally set to the address of PROM 8 is given is:
This is a memory area in which read prohibition data for prohibiting reading of the byte memory area is written in 16 of the PROM 8.

Therefore, the operation of this embodiment is to first write a program to a predetermined address of the PROM 8 via the write control circuit 7 and the internal data bus 11 using the PROM writer, and then write the program to a predetermined address of the PROM 8 via the internal data bus 11 and the read control circuit again. 6, the data is read out and confirmed. After that, information that prohibits the reading of data in this PROMB is written to the control circuit 7 and the internal data bus 1.
1 to register 9.

By writing data that prohibits the reading of the data written in the PROM 8 into the register 9 in this way, even if a third party tries to read the program using a PROM writer, the read prohibition signal lO written in the register 9 can be prevented. inhibits the read operation of the read control circuit 6, and reading of data from the PROM 8 is prevented.

When used by a user, the CPU 12. RAMI 3. The other control circuit 14 and PROM 8 allow normal operation.

〔Effect of the invention〕

As described above, the single-chip microcomputer of the present invention has the effect of preventing a third party from illegally copying a program by writing data to a register that controls reading.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a circuit block diagram of a conventional single-chip microcomputer. 1... Single chip microcomputer, 2... Address input terminal, 3... Old data bus, 4... Write control signal input terminal,
5... Group readout control signal input terminal, 6...
read control circuit, 7... write control circuit,
8...PROM. 9...Register, 10...Read inhibit signal, 11...Internal data bus, 12...
...CPU, 13...RAM, 14...
...Other control circuits, 15...I10 terminal. Agent Patent Attorney Oto Uchihara

Claims (1)

[Claims] In a single-chip microcomputer that incorporates a PROM with a capacity of 2^n bytes, it has an address input terminal with m bits added in addition to the n bits necessary to access the PROM, and (n+m) A PROM-structured register at an arbitrary address specified by a bit address input terminal, an internal data bus commonly connected to the PROM and the register, and a write control circuit and a read control circuit connected to the internal data bus. A single-chip microcomputer comprising: a read inhibit signal written in the register to control the read control circuit to inhibit reading of data written in the PROM.