JPH03219348A - Device for protecting external memory card - Google Patents

Abstract

PURPOSE:To economically protect a memory without applying excess load to software by switching a current bank to a corresponding bank only when an external memory card is accessed, and when the memory card is not accessed, switching the current bank to an unused bank. CONSTITUTION:When a memory card access request is generated from an application, an operating system (OS) 200 switches the memory bank used by the memory card 43 for the hardware of a handy terminal. After completing said operation, the CPU 1 can be allowed to access the memory card 43. After completing the access to the memory card 43, the OS 200 immediately switches the current bank to an unused bank and then returns the control to the application. Consequently, memory protection can be economically attained without applying excess load to the software.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention provides data stored in a memory card, which is an external storage device used in electronic equipment such as a handheld terminal, for example, in order to prevent a CPU from running out of control. , relates to an external memory card protection device that protects against unexpected accidents such as malfunctions caused by program bugs and the like.

(Prior art) Handy terminals mainly use CPUs such as the i808688, but unlike cPUs such as the 80286.386, such CPUs do not have access rights to memory that are restricted by switches. There is no sufficient functional support for this. Therefore, software running on such a CPU cannot provide any protection function to the memory area used by both the operating system and the application. In electronic devices such as non-day terminals to which a memory card is connected, there is practically no protection function for data in the memory card.

Further, although it is technically possible to add some kind of memory protection function to the memory card side, it is often omitted because this function is not necessarily required from the memory card side.

(Problems to be Solved by the Invention) As mentioned above, in electronic devices such as handy terminals that use a CPU such as the 18086.88, data stored in an externally connected direct address type memory card is Since there is no protection function against such data, there is a problem that data may be accidentally rewritten and important information may be lost.

Furthermore, there is a method of protecting the memory by performing an enable operation for each memory element, but this method places a burden on the circuit configuration and software, resulting in a problem of being inefficient and uneconomical.

The present invention has been made in view of the above, and its purpose is to provide an economical system that does not place a burden on software.
An object of the present invention is to provide an external memory card protection device that achieves memory protection.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the external memory card protection device of the present invention has a central processing unit that does not have a memory protection function, and has a central processing unit that does not have a memory protection function. An external memory card protection device for protecting information stored on a memory card in an electronic device to which an external memory card can be connected, the device comprising: a device larger than the memory area of the external memory card; A memory space consisting of a plurality of corresponding banks is set, and the memory area of the external memory card connected to the electronic device can be accessed only when the memory area of the external memory card is accessed. a bank switching means for switching to a bank corresponding to a memory area of a memory card; and a bank switching means for switching to a bank corresponding to a memory area of a memory card; and a bank switching means for switching to a bank corresponding to a memory area of a memory card; The gist of the present invention is to have a control means for controlling switching to a bank to be used.

(Function) In the external memory card protection device of the present invention, a memory space consisting of a plurality of banks each corresponding to the memory area of the external memory card is set, and only when the memory area of the external memory card is accessed, the external Switching is performed to a bank corresponding to the memory card, and if the memory area of the external memory card is not accessed, switching is performed to an unused bank that does not correspond to the memory area of the external memory card.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the overall hardware configuration of a day terminal to which an external memory card protection device according to an embodiment of the present invention is applied. The handheld terminal shown in the figure has, for example, 18
086, 88, and a program ROM 5.086 on the bus 3 connected to the CPUI. CGRO
M7. RAM9, keyboard 13 via keyboard interface 11, LCD 17 via LCD interface 15, buzzer 2 via buzzer controller 19
1. C-MOS via the first communication interface 23
Level level 1025, optical interface 29 via second communication interface 27, R3-232-C33 via third communication interface 31, printer 39 via printer controller 35 and printer driver 37, option interface 41 Memory card 43, RTC (calendar) 45, timer 47,
Interrupt controller 49 and clock generator 51
is connected.

FIG. 2 is a state transition diagram of a program sent to the non-day terminal shown in FIG. The data terminal is an application program 1 created by the user.
00 and an operating system (hereinafter abbreviated as O8) 20 provided along with the hardware as a device.
0 at the same time, the application 100 has 0S20
It operates in an environment where 0 services are provided. That is, the application does not directly operate special hardware, but only issues a request to O3, and O8 executes the application's request. Therefore, the application does not directly manipulate the memory space of the memory card, but
The memory card is designed so that it can only be accessed through the 8.

When the application requests access to the memory card as shown in section B in Figure 2, the O8 sends the memory card 43 to the hardware of the handy terminal.
O8 switches the memory bank to be used (step 210C0 in FIG. 2, and at this point it becomes possible to access the memory card 43 for the first time from the CPU (step 220). When the bank is finished, the bank is immediately switched to an unused memory area, and control is returned to the application in this state (step 230).When the bank is switched to an unused memory area in this way, the CPU 1 transfers the memory card 4
Area 3 becomes unusable.

Therefore, in the section indicated by A in FIG. 2, it is physically impossible for the CPU to access the memory in the memory card 43, so within this section A, the CPU may run out of control or the memory may be lost due to an application malfunction. Even if an abnormal access to the card occurs, the data in the memory card can be protected.

In an actual application, the operating time in the state of section A is sufficiently longer than that in section B, so that the information in the memory card can be effectively protected from abnormal access to the memory card.

FIG. 3 shows a memory map of the handy terminal of FIG. The lower 640 KB (kilobits) of the RAM memory is used as a program area, and the remaining 360 KB is managed by the device. The example shown in the figure shows hardware having a 64 KB window and 256 banks of switching. Therefore, a memory card can have a maximum capacity of 64KB x 2'56-16MB. If a 128 KB memory card is inserted here, the O8 will keep the window facing the last bank in section A of FIG. 2, and the CPU will not be able to directly access the memory in the memory card. In this way, it is configured to have a wider bank than the memory card supported by the handy terminal, and is configured so that accesses to banks without the corresponding hardware do not affect the memory of the actual memory card. ing. As a result, since no special operations are performed on the memory card, a commercially available general memory card can be used.

〔Effect of the invention〕

As explained above, according to the present invention, a memory space consisting of a plurality of banks each corresponding to the memory area of an external memory card is set, and only when the memory area of the external memory card is accessed, the external memory If the memory area of the external memory card is not accessed, the bank is switched to the bank that corresponds to the card, and if the memory area of the external memory card is not accessed, it is switched to an unused bank that does not correspond to the memory area of the external memory card, so there is no burden on the software. Therefore, it is possible to economically protect the memory and protect the information in the external memory card from memory destruction due to abnormal operation. Furthermore, since there is no need to provide special hardware to the memory card, a commercially available general memory card can be used, which has a great advantage in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall hardware configuration of a handy terminal to which an external memory card protection device according to an embodiment of the present invention is applied, and FIG. 2 is a state transition of a program in the handy terminal shown in FIG. FIG. 3 is a diagram showing a memory map of the handy terminal of FIG. 1. 1. ・CPU. 43. ・Memory card, 100. ・Application program, 200.
·operating system.

Claims (1)

[Claims] External memory card protection for protecting information stored on a memory card in an electronic device that has a central processing unit without a memory protection function and can connect a direct address type external memory card to the central processing unit. a memory space of a plurality of banks, each of which is larger than a memory area of an external memory card, and each bank corresponds to a memory area of the external memory card; hang switching means for switching to a bank corresponding to a memory area of the external memory card so that the memory area of the external memory card can be accessed only when the memory area of the external memory card is accessed; An external memory card protection device comprising: control means for controlling switching to an unused bank that does not correspond to the memory area of the external memory card when the memory area of the external memory card is not accessed.