SEMICONDUCTOR MEMORY AND DATA ACCESS METHOD

Abstract

While a semiconductor memory operates in a first operation mode with high security, an encrypted command is inputted and then decoded to acquire the first address information. After the semiconductor memory comes into a second operation mode where the level of security is lower than that of the first operation mode, a command is inputted. Then, the second address information is acquired from the command. A control circuit in the semiconductor memory generates an address of 10 bits by using the first address information as a high-order 4 bits and the second address information as a low-order 6 bits and outputs the address to a memory array. With this operation, it becomes possible to read/write data from/to the memory array.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an information processing apparatus which accesses a semiconductor memory;

FIG. 2 is a functional block diagram showing the semiconductor memory;

FIG. 3 is a flowchart showing an operation flow of a control circuit, from extraction of the first and second address information to output of a specified address;

FIG. 4 is a flowchart showing an operation flow for generation of the specified address in accordance with a first preferred embodiment; and

FIG. 5 is a flowchart showing an operation flow for generation of the specified address in accordance with a second preferred embodiment.

Claims

1. A semiconductor memory, comprising: a data memory part;a control circuit; andan input/output circuit,wherein said semiconductor memory is a memory which operates, switching between a first operation mode and a second operation mode and said first operation mode ensures higher security for a command than said second operation mode,said control circuit comprisesan operation mode memory part for storing a current operation mode therein, anda command discrimination circuit for discriminating a command inputted from the outside through said input/output circuit,said command discrimination circuit includesa means of deciphering a command by loosening the security for said command inputted in at least said first operation mode,a means of acquiring first address information from a command inputted in said first operation mode, anda means of acquiring second address information from a command inputted in said second operation mode,said control circuit further comprisesan address information memory part for storing said first address information therein, which is acquired by said command discrimination circuit in said first operation mode, andan address generator circuit for generating a specified address from all or part of said second address information acquired by said command discrimination circuit in said second operation mode and all or part of said first address information stored in said address information memory part, andsaid control circuit accesses said data memory part by using said specified address outputted from said address generator circuit.

2. The semiconductor memory according to claim 1, wherein said first address information forms a high-order bit address of said specified address and said second address information forms a low-order bit address of said specified address.

3. The semiconductor memory according to claim 2, wherein said data memory part is divided into a plurality of blocks to be controlled,said high-order bit address is a block address of said data memory part, andsaid command discrimination circuit acquires said high-order bit address and memory areas in a block designated by said high-order bit address can be thereby sequentially accessed in said second operation mode.

4. The semiconductor memory according to claim 3, wherein blocks other than said block designated by said high-order bit address can not be substantially accessed in said second operation mode.

5. The semiconductor memory according to claim 3, wherein said data memory part consists of a plurality of blocks which are designated by block addresses of different bit lengths.

6. The semiconductor memory according to claim 1, wherein a certified value is included in a command inputted in said first operation mode, andif a certified value included in a command inputted in said second operation mode coincides with said certified value inputted in said first operation mode, access to said data memory part is enabled.

7. A semiconductor memory, comprising: a data memory part;a control circuit; andan input/output circuit,wherein said semiconductor memory is a memory which operates, switching between a first operation mode and a second operation mode and said first operation mode ensures higher security for a command than said second operation mode,said control circuit comprisesan operation mode memory part for storing a current operation mode therein, anda command discrimination circuit for discriminating a command inputted from the outside through said input/output circuit,said command discrimination circuit includesa means of deciphering a command by loosening the security for said command inputted in at least said first operation mode,a means of acquiring first address information from a command inputted in said first operation mode, anda means of acquiring second address information from a command inputted in said second operation mode,said control circuit further comprisesan address information memory part for storing said first address information therein, which is acquired by said command discrimination circuit in said first operation mode, andan address generator circuit for comparing all or part of said second address information acquired by said command discrimination circuit in said second operation mode with all or part of said first address information stored in said address information memory part and generating a specified address from all or part of said second address information only if these coincide with each other, andsaid control circuit accesses said data memory part by using said specified address outputted from said address generator circuit.

8. The semiconductor memory according to claim 7, wherein said data memory part is divided into a plurality of blocks to be controlled,said first address information is a block address of said data memory part,said second address information is an address corresponding to a unit of access of said data memory part, andsaid address generator circuit outputs said second address information as a specified address if a high-order block address included in said second address information coincides with said first address information.

9. The semiconductor memory according to claim 8, wherein said command discrimination circuit acquires said first address information and memory areas in a block designated by said first address information can be thereby sequentially accessed in said second operation mode.

10. The semiconductor memory according to claim 9, wherein blocks other than said block designated by said first address information can not be substantially accessed in said second operation mode.

11. The semiconductor memory according to claim 8, wherein said data memory part consists of a plurality of blocks which are designated by block addresses of different bit lengths.

12. The semiconductor memory according to claim 7, wherein a certified value is included in a command inputted in said first operation mode, andif a certified value included in a command inputted in said second operation mode coincides with said certified value inputted in said first operation mode, access to said data memory part is enabled.

13. A data access method of accessing a data memory part in a semiconductor memory which comprises said data memory part, a control circuit and an input/output circuit, wherein said semiconductor memory is a memory which operates, switching between a first operation mode and a second operation mode,said method comprising the step ofa) inputting a command from the outside by using said control circuit in a state where said semiconductor memory operates in said first operation mode with higher security for a command than said second operation mode;b) acquiring first address information from a command inputted in said first operation mode by said control circuit;c) bringing said semiconductor memory into said second operation mode;d) inputting a command from the outside by using said control circuit in a state where said semiconductor memory operates in said second operation mode;e) acquiring second address information from a command inputted in said second operation mode by said control circuit;f) generating a specified address from all or part of said first address information and all or part of said second address information by using said control circuit; andg) accessing said data memory part by using said generated specified address by said control circuit.

14. The data access method according to claim 13, wherein said first address information forms a high-order bit address of said specified address and said second address information forms a low-order bit address of said specified address.

15. The data access method according to claim 14, wherein said data memory part is divided into a plurality of blocks to be controlled,said high-order bit address is a block address of said data memory part, andafter said high-order bit address is acquired by executing said steps a) to c), memory areas in a block designated by said high-order bit address can be thereby sequentially accessed in said second operation mode by repeating said steps d) to g).

16. The data access method according to claim 15, wherein blocks other than said block designated by said high-order bit address can not be substantially accessed in said second operation mode.

17. The data access method according to claim 15, wherein said data memory part consists of a plurality of blocks which are designated by block addresses of different bit lengths.

18. The data access method according to claim 13, wherein a certified value is included in a command inputted in said first operation mode, andif a certified value included in a command inputted in said second operation mode coincides with said certified value inputted in said first operation mode, access to said data memory part is enabled.

19. A data access method of accessing a data memory part in a semiconductor memory which comprises said data memory part, a control circuit and an input/output circuit, wherein said semiconductor memory is a memory which operates, switching between a first operation mode and a second operation mode,said method comprising the step ofa) inputting a command from the outside by using said control circuit in a state where said semiconductor memory operates in said first operation mode with higher security for a command than said second operation mode;b) acquiring first address information from a command inputted in said first operation mode by said control circuit;c) bringing said semiconductor memory into said second operation mode;d) inputting a command from the outside by using said control circuit in a state where said semiconductor memory operates in said second operation mode;e) acquiring second address information from a command inputted in said second operation mode by said control circuit;f) comparing all or part of said first address information with all or part of said second address information by using said control circuit and generating a specified address from all or part of said second address information by using said control circuit only if these coincide with each other; andg) accessing said data memory part by using said generated specified address by said control circuit.

20. The data access method according to claim 19, wherein said data memory part is divided into a plurality of blocks to be controlled,said first address information is a block address of said data memory part,said second address information is an address corresponding to a unit of access of said data memory part, andsaid second address information is outputted as a specified address in said step f) if a high-order block address included in said second address information coincides with said first address information.

21. The data access method according to claim 20, wherein said first address information is acquired in said steps a) to c) and memory areas in a block designated by said first address information can be thereby sequentially accessed in said second operation mode by repeating said steps d) to g).

22. The data access method according to claim 21, wherein blocks other than said block designated by said first address information can not be substantially accessed in said second operation mode.

23. The data access method according to claim 20, wherein said data memory part consists of a plurality of blocks which are designated by block addresses of different bit lengths.

24. The data access method according to claim 19, wherein a certified value is included in a command inputted in said first operation mode, andif a certified value included in a command inputted in said second operation mode coincides with said certified value inputted in said first operation mode, access to said data memory part is enabled.