JPH02287742A - Nonvolatile memory with storage protecting function - Google Patents

Abstract

PURPOSE:To eliminate problems regarding reliability control and enable maintenance such as the rewriting of stored information even after the storage by rewriting main information, unlock information, and lock information by using the unlock information and lock information. CONSTITUTION:The nonvolatile memory 1 is stored with the main information to be stored and protected, the unlock information as a key for enabling the main information to be read and written, and the lock information as a key for inhibiting the main information from being read and written, a bus switching circuit 2 switches and connects the memory bus from the nonvolatile memory 1 to an internal bus or an external bus linked with an external circuit, and a storage protecting circuit 3 is provided. The unlock information and lock information on the nonvolatile memory 1 are matched with external unlock information which is inputted from the external bus to enable operation such as rewriting. Consequently, problems regarding maintenance and reliability control are eliminated, information to be protected is enabled to be written and rewritten thereafter optionally, and secure and safe storage protection is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a non-volatile memory used in any processing device and storing non-public information, and in particular,
The present invention relates to a non-performable memory with a memory protection function that not only allows the private information to be rewritten arbitrarily but also prevents unauthorized access from outside.

(Prior art) In the case of IC memory, for example, which is a non-volatile memory whose memory is protected even when the power is turned off, after the necessary access is made at the production stage and predetermined private information is stored,
Methods such as cutting the C pin or blowing out a special internal fuse are used to cut the control signal line that allows access from the outside, making it impossible to access the stored information from the outside. There is.

However, with such conventional methods, operations such as rewriting the stored information after production is completed are completely impossible, and even if a part of the information needs to be changed, there is no means to change it and a new product must be produced. etc., maintenance problems arise. Also, I
There are problems such as the need to manage the reliability of the C-pin and fuse cutting operations.

(Object of the Invention) The object of the present invention is to eliminate maintenance and reliability management problems that occur in the conventional method, and to enable writing and rewriting of information to be protected at will after production is completed. The object of the present invention is to provide a nonvolatile memory with a memory protection function that has reliable and safe memory protection means.

(Structure and operation of the invention) [Structure] The nonvolatile memory with a memory protection function according to the present invention includes main information to be protected and predetermined open key information that is a key to enable reading and writing of the main information. a non-volatile memory that stores the key information and opening key information that prohibits reading and writing of the main information; and a bus that switches and connects the memory bus from the non-volatile memory to either an internal bus or an external bus that connects to an external circuit. a switching circuit, and a storage section connected to the internal bus and the external bus to fixedly store internal information at predetermined intervals, and when the power is turned on, the memory bus is switched to the internal bus and connected to the non-volatile bus. If the read out key information and the open key information input from the external bus are matched, or if the read out key information matches the open key information input from the external bus, or The released open key information and the internal information are compared, and only when the two pieces of information do not match, the memory bus is switched and connected to the external bus, and the non-volatile memory is accessed from the outside via the external bus. The present invention is characterized by comprising a memory protection circuit that performs control so that main information, open key information, and open key information can be rewritten.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a diagram showing an example of the configuration of a nonvolatile memory with a memory protection function according to the present invention.

In the figure, ■ is a nonvolatile memory, 2 is a bus switching circuit,
3 is a memory protection circuit.

[For production]

The operation of the nonvolatile memory with memory protection function of the present invention based on the configuration example shown in FIG. 1 will be explained in detail below using FIG. 2.

FIG. 2 is an example of a flowchart showing the operation of the memory protection circuit 3 shown in FIG. ing.

In FIG. 2, when the power is turned on (START) to the device, the memory protection circuit 3 first enters step 31 and transfers the memory bus MB to the internal bus IB by operating the bus switching circuit 2 using the bus switching control signal BC. and prohibits access to memory bus MB from external bus OB.

Next, the process proceeds to step 32, where the predetermined and written open key information and open key information, which are used for the purpose of opening the memory bus MB to the external bus OB and the purpose of closing the memory bus MB without opening it, are made non-volatile. The data is read from a predetermined address in the data memory 1 via the internal bus IB and stored at - time.

In step 33, the process waits for input of open groove external information corresponding to the above-mentioned key open information from the outside via the external bus OB. Here, the memory protection circuit 3 maintains a state in which access from the external bus OB to the memory bus MB is prohibited when there is no input of unlocking external information from the external bus OB, and the unlocking external information manual input is prohibited. If so, in the next step 34, the open key information is compared with the open groove external information, and it is determined that a predetermined rule (for example, a complete match relationship, a two-part match relationship, a specific function relationship, etc.) is established between the two pieces of information. If it is true, the process advances to step 35 to release the memory bus MB to the external bus OB.

That is, in step 35, by operating the bus switching circuit 2 with the bus switching control signal BC, the memory bus MB is switched and connected to the external bus OB, the prohibition of access from the external bus OB to the memory bus MB is canceled, and the flow is started. end.

On the other hand, in the verification at step 34, if the rule is not satisfied, the process proceeds to step 36. Here, the intermittent internal information fixedly stored in advance inside the memory protection circuit 3 and the above-mentioned open key information read from the non-volatile memory 1 are compared, and the above-mentioned information is If the established rules are satisfied, the flow is completed in step 31 with access from the external bus OB to the memory bus MB being prohibited. If the rule is not established, the process proceeds to step 35, and as described above, the memory bus M
B is switched to the external bus OB, the memory bus MB is opened to the outside, and the flow ends.

Note that the flowchart of the operation shown in FIG. 2 is an example, and the order of the collation may be reversed from that in FIG. 35) The condition for entering is limited to when the agreement is established by comparing the open key information and the open key external information, or the agreement is not established by comparing the open key information and the intermittent internal information. Bye.

The handling from production to shipment of the nonvolatile memory with memory protection function of the present invention having means for performing the above operations and the characteristics of the memory protection function will be described below.

First, the memory protection circuit 3 stores predetermined intermittent internal information in a non-volatile state! Even if the information to be protected and the contents of the open key information in the nonvolatile memory 1 are unwritten and undefined at the time when the production of the functional nonvolatile memory is completed, when the power is turned on, the open key information will be deleted. (undefined at this point) and the intermittent internal information, the probability that the rules coincide by chance can be made extremely small by increasing the amounts of both pieces of information. Therefore,
At the time of completion of production, the memory bus MB of the nonvolatile memory 1 is switched and connected to the external bus OB almost without exception, so that the unwritten contents of the nonvolatile memory 1 can be freely read and written.

Next, after writing non-public information (main information) that is subject to predetermined storage protection into a predetermined area of the non-volatile memory 1, predetermined non-public open key information is written in the open key information area.
In the open key information area, open key information (which may be made public) established by the regulations is written by checking with the above-mentioned intermittent internal information.Finally, the power is turned off and the product is shipped.

When the power is turned on again to the memory of the present invention through the above procedure, the memory protection circuit 3 checks the open key information and establishes an open key that meets the rules, according to the flowchart example of the operation explained in FIG. Unless key external information (information known only to the person who previously wrote the open key information) is manually input from the external bus OB, the above-mentioned action of the open key information will cause the memory bus M to
It can be seen that since the connection of B to the external bus OB is prohibited, all information in the non-volatile memory 1 is safely protected.

(Effects of the Invention) As described in detail below, according to the present invention, since physical irreversible processing such as cutting off IC pins and fuses is not used to protect stored information, reliability management problems are avoided. Not only can this problem be solved, but maintenance such as rewriting the stored information can be performed even after production is completed.

Furthermore, in the maintenance of the above-mentioned stored information, the length of the necessary private closed key and closed key information can be made sufficiently long, so that the function of preventing unauthorized access can be sufficiently performed and the stored The protection has advantages such as being reliable and safe.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration example of a nonvolatile memory with a memory protection function according to the present invention, and FIG. 2 is an example flowchart showing the operation of the memory protection circuit of FIG. 1. 1... Non-volatile memory, 2... Bus switching circuit, 3...
...Memory protection circuit, 31-36...Processing step.

Claims (1)

[Scope of Claims] Main information to be memory protected, predetermined open key information that is a key that enables reading and writing of the main information, and closed key information that is a key that prohibits reading and writing of the main information. a bus switching circuit that switches and connects a memory bus from the nonvolatile memory to either an internal bus or an external bus leading to an external circuit; and a storage unit that permanently stores closed key internal information, and when the power is turned on, the memory bus is switched to the internal bus and the open key information and the closed key information are read from the nonvolatile memory. If the read open key information and the open key external information input from the external bus are matched, or if the read closed key information and the closed key internal information are matched, Only when the two pieces of information do not match, the memory bus is switched and connected to the external bus, and the main information, open key information, and closed key information of the nonvolatile memory are rewritten from the outside via the external bus. A nonvolatile memory with a memory protection function, which is equipped with a memory protection circuit that performs control to ensure that the memory is protected.