Memory card including copy protection

• US 5,131,091 A
• Filed: 03/14/1989
• Issued: 07/14/1992
• Est. Priority Date: 05/25/1988
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Mizuta, Masaharu
• Primary Examiner(s): Heckler, Thomas M.
• Application Number:
  US07/322,993
• Time in Patent Office: 1,218 Days
• Field of Search: 364/200 MS File, 364/900 MS File, 395/725, 395/700
• US Class Current: 726/32
• CPC Class Codes: G06F 21/79 in semiconductor storage media, e.g. directly-addressable memories
• CPC Class Codes: G11C 7/24 Memory cell safety or protection circuits, e.g. arrangements for preventing inadvertent reading or writing; Status cells; Test cells

Abstract

Data for protecting software is written into a ROM for protecting software in an IC card including other ROMs for storing data and scrambled software. The data for protecting software provides a key for execution of the software. A read-write RAM is responsive to the same select signal that is applied to the software protecting ROM for reading and writing of data by a user. When the data of the software protecting ROM is read out, the outputs of the ROM and the RAM are exclusive-OR gated. Accordingly, it is impossible to easily know what software protection data has been written into the ROM, i.e., to decode the software key. The ROM, the RAM, and the data processing circuit may be constructed as one IC.

Claims

1. A memory card comprising:

system bus means for signal transfer;

software storing means connected to said system bus means for storing data and at least one computer program, i.e., software, and for outputting the stored data and software to the system bus means in response to a read signal;

selecting means for generating a chip select signal;

software protecting memory means connected to said selecting means and said system bus means for storing software protecting data and for outputting to said system bus means said software protecting data in response to the chip select signal;

read-write memory means connected to said selecting means and said system bus means responsive to the chip select signal for storing read-write data received from the system bus; and

data processing means connected to said system bus means for exclusive-OR gating of the read-write data output from said read-write memory means and said software protecting data output from said software protecting memory means to produce processed data, and for outputting the processed data to the system bus means whereby the software protecting data stored in said software protecting memory means may be obtained.

2. A memory card according to claim 1 wherein said software storing means comprises at least one ROM, said software protecting memory means comprises at least one ROM, said read-write memory means comprises at least one RAM, said selecting means comprises a chip select circuit for decoding a select signal to generate the chip select signal for access to one of said software storing means, said read-write memory means, and said software protecting memory means, and said data processing means comprises an exclusive-OR gate for gating the data output by said read-write memory means and said software protecting memory means.

3. A memory card according to claim 2 wherein each of said software protecting memory means, said read-write memory means and said data processing means comprises discrete ICs.

4. A memory card according to claim 2 wherein said software protecting memory means, said read-write memory means and said data processing means are constituted by a single IC.

5. A memory card according to claim 2 wherein said software protecting memory means, said read-write memory means and said data processing means comprises a single gate array IC.

6. A memory card according to claim 1 wherein said data processing means comprises an exclusive-OR gate for exclusive-OR gating of data output by said read-write memory means and by said software protecting means;

a first buffer circuit having an input and an output for providing the state of its input at its output only when a control signal is in a first of two possible states; and

a second buffer circuit having an input and an output for providing the state of its input at its output only when the control signal is in a second of the two possible states, the output of said first buffer circuit being connected to said read-write memory means for storing data in said read-write memory means and the input of said second buffer circuit receiving data produced by said exclusive-OR gate for outputting data from said software protecting memory means and said read-write memory means.

7. A memory card according to claim 1 wherein said memory card employs 8-bit data.

8. A memory card according to claim 1, wherein said memory card employs 16-bit data.

9. A memory card according to claim 1, wherein said memory card employs 32-bit data.