JPH0337885A - Rom card - Google Patents

Abstract

PURPOSE:To keep the secrecy of data in a ROM by prohibiting the readout of the content of the ROM unless a decided value is written from a microcomputer system to a built-in register in a ROM card. CONSTITUTION:When write from the microcomputer system to a specific input/ output address or memory address is performed, a write signal is supplied from a decoder 5 to a register 6, and a value inputted to the register 6 is written. An inputted value is compared with the value decided in advance at a comparator 7. When coincidence is obtained, the output of the comparator 7 is inputted to a gate circuit 8. The gate 8 reads out the content of a selection signal for built-in ROMs 91-9n generated at the decoder 5 from a corresponding ROM chip when the output of the comparator 7 is activated (coincidence). No readout is performed when noncoincidence is obtained. The secrecy of the built-in ROM can be kept by employing such constitution.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a ROM card.

[Conventional technology]

Conventional ROM cards have a built-in ROM and a control circuit that generates selection signals, so the electrical connections between the address bus, data bus, control signals, and power supply are established correctly between the microcomputer system and the ROM. If so, the microcomputer system uses the R inside the ROM card.
I was able to read the contents of OM.

[Problem to be solved by the invention]

In the conventional memory cards mentioned above, the physical specifications of the interfaces are becoming standardized, so compared to ROM cards whose memory card interfaces have standard specifications, specific models in the microcomputer system to be connected are There are problems in that the data in the built-in ROM cannot be kept secret, and cannot be accessed by other models.

[Means to solve the problem]

The ROM card of the present invention is a ROM that has a built-in ROM inside the card, which is used by connecting to a system bus of a microcomputer system via a connector.
The card includes a register that can write any value from the microcomputer system to the ROM card, and a register that determines whether or not the value written to the register matches a predetermined value. a comparator circuit that activates an output at times, and a comparator circuit that permits access to the ROM from the microcomputer system only when the output of the comparator circuit is activated; This configuration includes a gate circuit that controls not to permit access to the ROM from the system.

〔Example〕

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

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

1 is a connector connected to the system bus of the system main body. 2.3.4 is an address bus.

These are buffers for the control bus and data bus. A decoder 5 generates selection signals for the ROMs 91 to 9n and write signals to the register 6 according to the values of the address bus and the control bus. register 6
When the microcomputer system writes to a specific input/output address or memory address, a write signal is generated and supplied by the decoder 5, and the value input to the register 6 is written. This input value is compared to the comparison circuit 7.
Compare whether or not it matches a predetermined value. If they match, the output of the comparison circuit 7 is activated; if they do not match, it becomes inactive. The output of this comparison circuit 7 is input to a gate circuit 8. The gate circuit 8 transfers the selection signal for the internal ROMs 91 to 9fi generated by the decoder 5 to the corresponding RO when the output of the comparison circuit 7 is active.
The contents are read from the M chip, and if it is in an inactive state, the contents are controlled not to be output.

〔Effect of the invention〕

As explained above, the present invention makes it possible to prevent the contents from being read out unless a predetermined value is written into the register built into the ROM card from the microcomputer system, making it possible to keep the data in the built-in ROM secret. There is an effect that can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention. 1...Connector, 2...Address bus buffer, 3
...Control bus buffer, 4...Data bus buffer, 5...Decoder, 6...Register, 7.
...Comparison circuit, 8...Gate circuit, 91-9fi...
・ROM chip.

Claims (1)

[Claims] Among memory cards used by connecting to the system bus of a microcomputer system via a connector, the ROM card has a built-in ROM, and the ROM is
A register that can write any value from the microcomputer system to the M card, and a comparison that determines whether the value written to the register matches a predetermined value and activates the output when it matches. access to the ROM from the microcomputer system is permitted only when the output of the comparison circuit is activated, and access to the ROM from the microcomputer system is permitted when the output of the comparison circuit is inactive. A ROM card characterized by having a gate circuit that controls not to permit.