JPH1011365A - Protecting circuit for nonvolatile storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protecting circuit for the nonvolatile storage device which protects data in the nonvolatile storage device by detecting a fall in source voltage in its early stage and performing proper protecting operation. SOLUTION: A source voltage detecting circuit is composed of an A/D converter 6 which converts an analog signal being a detected voltage into a digital signal and outputs it, and an operation table 7 which stores an operation program corresponding to the detected voltage is provided; and a control part 1 controls protecting operation for writing and reading according to the operation program stored in the operation table, so a drop in source voltage is detected early and proper protecting operation is carried out to protect the data in the nonvolatile storage device 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for an electrically rewritable nonvolatile memory device, and more particularly, to a protection circuit for an electrically rewritable nonvolatile memory device.
The present invention relates to protection of write data when a voltage drops.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional nonvolatile storage device (hereinafter referred to as E
FIG. 2 is a block diagram illustrating a configuration of a control circuit of a device such as an air conditioner using an EPROM. In the figure, 1 is a control unit, 2 is a PROM in which a program is written, 3 is a RAM, 4 is a driving unit 4 such as a temperature detector 4a, a blower fan, etc.
b is a controlled device, and 5 is an EEPROM, 60 is a power supply voltage detector. At the time of the normal voltage, the control unit 3 stores the detection data from the temperature detector 4a and the operation mode at that time in the RAM 3 in accordance with the program written in the PROM 1 and stores the detected data in the RAM 3 while referring to the contents of the RAM 3. It operates to control the driving unit 4b. Now, if the power supply voltage drops below a predetermined value for some reason during operation, the power supply voltage detector 60 detects this, and when the control unit 1 receives the detection signal, the operation mode and the like stored in the RAM Is written to the EEPROM 5 and saved, and when the power is restored, the EEPROM
The data written in the ROM 5 is read and written in the RAM 3, and the operation before the power is turned off is restarted.
However, in such a protection circuit for a nonvolatile memory device,
When the amount of data written in the RAM 3 increases, the power supply voltage drops below the operable voltage of the EEPROM 5 during writing, and all data on the RAM 3 cannot be written.
There is a problem that abnormal operation is performed because incomplete data in which some data is missing is written. In order to solve such a problem, a capacitor or the like is generally inserted in the power supply of the control system to delay the drop of the power supply voltage. However, when there is much data to be written to the EEPROM 5, writing takes time, and the voltage drops during writing, which may cause a writing failure.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, detects a drop in power supply at an early stage, and performs an appropriate protection operation to protect data in a nonvolatile storage device. It is an object to provide a protection circuit for a storage device.

[0004]

According to the present invention, there is provided a power supply voltage detecting circuit for detecting a power supply voltage.
A protection circuit configured to control the writing and reading of the electrically rewritable nonvolatile storage device when the power supply voltage falls below a predetermined value. The power supply voltage detection circuit includes an A / D converter that converts an analog signal of a detection voltage into a digital signal and outputs the digital signal. An operation table for storing an operation program corresponding to the detection voltage is provided, and the operation table is stored in the operation table. According to the operation program, the control unit controls to perform write and read protection operations.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS With the above-described configuration, in the protection circuit of the nonvolatile memory device according to the present invention, the power supply voltage is converted into a digital signal by the A / D converter, and the digital signal is input to the control unit. The unit refers to the operation table and performs write and read protection operations of the nonvolatile memory device by an operation program corresponding to the detection voltage.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a protection circuit of a nonvolatile memory device according to the present invention. FIG. 1 is a block diagram showing an embodiment of a protection circuit of a nonvolatile memory device according to the present invention. In the drawing, the same symbols are used for the same functions as in FIG. 4 and the description is omitted, and 6 is an A / D converter.
The power supply voltage is converted into a digital signal and input to the control unit 1. Reference numeral 7 denotes an operation table provided in a partial area of the PROM 2. The operation table 7 stores an operation program corresponding to the power supply voltage. In the case of this embodiment, PR
Although the area of the operation table 7 is provided on the OM 2, it can be understood that the area of the operation table 7 may be provided on the EEPROM 5 although not shown.

Next, the operation of the above configuration will be described. The power supply voltage data digitally converted by the A / D converter 6 is always input to the control unit 1.
Monitors the data at regular time intervals (ST0), determines the operation by referring to the operation table 7, and controls each unit. FIG. 2 shows an embodiment of the operation table 7, and FIG. 3 shows an operation flow thereof. The operation will be described below with reference to FIG. When the power supply voltage is 4 to 5 volts, the control of the normal operation described in the related art section is performed. (ST
1) When the power supply voltage becomes 3 to 3.9 volts, monitor the power supply voltage at intervals of 1/2 to 1/4 of normal, strengthen monitoring, and know the voltage drop as soon as possible. I can do it. (ST2)

When the power supply voltage drops below 2.9 volts, the contents of the RAM 3 are written into the EEPROM 5 (ST3). When the power supply voltage becomes 2.5 volts or less during writing, the data on the RAM 3 is invalidated and reset. After creating the instructed data (ST4), the writing is continued until the writing is completed. When the power supply voltage falls to 2 volts or less, when the necessary data in the RAM 3 has been completely written into the EEPROM 5, the rewriting and the operation are stopped as normal termination (ST).
5) If the writing has not been completed, the data for instructing the reset which has been created is stored in the EEPROM from the RAM 3.
After the writing into ST5 (ST6), the rewriting and the operation are stopped (ST5).

Next, the operation when the power is restored will be described. As described above, when the necessary data in the RAM 3 is completely written in the EEPROM 5, when the power is restored and the normal voltage (4 to 5 volts) is reached, the EEPROM is turned on.
If the control unit 1 reads the contents of the ROM 5 and data for instructing reset is not written, the contents of the EEPROM 5 are written to the RAM 3 to return to the operation state before the power is turned off based on the data in the RAM 3. If the power supply voltage drops to 2.5 volts or less before the writing is completed, the power supply is restored to the normal voltage (4 to 5 volts).
Is reached, the control unit 1 reads the data indicating the reset written in the EEPROM 5, writes the initial operation data written in the PROM 2 in advance in the RAM 3, and controls based on the initial operation data. I have.

[0010]

As described above, according to the protection circuit of the nonvolatile memory device according to the present invention, the power supply voltage is converted into a digital signal by the A / D converter and input to the control unit, and the control unit operates. With reference to the table, the operation program corresponding to the power supply voltage is controlled so as to perform the write and read protection operation of the EEPROM. Therefore, it is possible to detect a drop in the power supply early and perform an appropriate protection operation. A protection circuit for a nonvolatile storage device that protects data in the nonvolatile storage device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a protection circuit of a nonvolatile memory device according to the present invention.

FIG. 2 is a diagram showing one embodiment of an operation table of a protection circuit of the nonvolatile memory device according to the present invention.

FIG. 3 is a diagram showing an operation flow of an embodiment of the protection circuit of the nonvolatile memory device according to the present invention.

FIG. 4 is a block diagram showing a protection circuit of a conventional nonvolatile memory device.

[Explanation of symbols]

 Reference Signs List 1 control unit 2 PROM 3 RAM 4 controlled device 5 EEPROM (writable nonvolatile storage device) 6 A / D converter 7 operation table

Claims (5)

[Claims] 1. A power supply voltage detection circuit for detecting a power supply voltage, and a control unit, wherein when the power supply voltage falls below a predetermined value, writing and reading of an electrically rewritable nonvolatile memory device are stopped. In the protection circuit of the nonvolatile memory device controlled to perform the operation, the power supply voltage detection circuit is configured by an A / D converter that converts an analog signal, which is a detection voltage, into a digital signal and outputs the digital signal. A protection circuit for a nonvolatile memory device, comprising: an operation table for storing a corresponding operation program, wherein a control unit controls writing and reading operations according to the operation table. 2. The protection circuit according to claim 1, wherein the area of the operation table is provided in the nonvolatile storage device. 3. The protection circuit according to claim 1, wherein the area of the operation table is provided in a program ROM. 4. The protection circuit for a nonvolatile memory device according to claim 1, wherein an instruction for instructing a timing of monitoring a voltage is stored in the operation table. 5. The protection circuit according to claim 1, wherein a protection data creation command indicating validity of data is stored in the operation table.