JP2000348491A - Non-volatile memory and microcomputer - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the long write time of a memory cell of a microcomputer with built-in nonvolatile memory. SOLUTION: When rewriting a nonvolatile memory, the number of rewrites is counted, and the rewrite time is increased by increasing the rewrite voltage according to the number of rewrites, thereby minimizing a change in rewrite time with the number of rewrites.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer having a built-in nonvolatile memory.

[0002] Counting the number of times of rewriting of a memory cell, storing the number of times of rewriting in a memory cell, judging the number of times stored, and varying a rewriting voltage according to the number of times, minimizes the increase in rewriting time by the number of times of rewriting. It is intended to prevent this.

[0003]

2. Description of the Related Art In recent years, development periods of various electric appliances have been shortened, and with respect to a microcomputer mounted on a system board of the electric appliance, a flash memory or the like is provided so that a program can be written or rewritten under the control of a CPU after the mounting. However, there is a strong demand for a microcomputer having a built-in nonvolatile memory, and the number of rewrites can be reduced from 100 times to 1000
The number of times has been increasing year by year to zero.

Hereinafter, a nonvolatile memory built in a microcomputer will be described.

FIG. 4 is a schematic diagram illustrating a microcomputer with a built-in nonvolatile memory. 1 is a rewrite voltage and 2 is a rewrite voltage generation circuit.

Conventionally, a constant voltage is generated from a boosted voltage by a clamp diode, and a ladder resistor is divided to generate a rewrite voltage.

[0007]

However, in the above-mentioned conventional microcomputer with a built-in nonvolatile memory, when rewriting is repeated, a problem arises that the rewriting time becomes longer than the initial time in accordance with the number of rewriting due to deterioration of the film thickness and the like. Therefore, in a system in which the number of times of rewriting is large, it is necessary to design the system in consideration of the guaranteed rewriting time after the number of times of rewriting.

FIG. 5 is a characteristic diagram of the number of rewrites and the rewrite time of the conventional microcomputer with a built-in nonvolatile memory, and shows the characteristic that the rewrite time increases as the number of rewrites increases.

[0009]

According to the present invention, a rewrite frequency storage is provided in a part of a memory, and has a function of updating and storing the number of rewrites for each rewrite. , The function of varying the rewrite voltage.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

1 is a microcomputer, 2 is a memory cell array, 201 is an area for storing the number of rewrites in the memory cell array, 3 is a voltage variable register, 401 to 403 are switches for changing a rewrite source voltage, and 5 is a rewrite source. A voltage generation circuit, 6 is a selected rewrite voltage, and 7 is a bus. When rewriting two memory cells by two memory cells and three voltage variable registers connected to one microcomputer and seven buses, the microcomputer reads the rewrite count storage memory,
In order to determine the number of rewrites and compare with the number of rewrites stored in the ROM in advance to select a voltage to be used according to the number of rewrites, the voltage variable registers for rewriting the three voltage variable registers are used to change the voltages of 401, 402 and 403. Select one of the variable switches. At the beginning of rewriting, the switch 403 is selected. When the number of times of rewriting becomes equal to or more than a certain number, the selected switch is selected to 402 and further to 401, and the increased rewriting voltage is supplied to the rewriting voltage of 6. . When writing data, add the number of rewrites to the rewrite number storage memory.
The value of 1 is stored again in the memory for storing the number of times of rewriting of the memory cell. FIG. 2 is a characteristic diagram of the number of rewrites and the rewrite voltage of the present invention, showing that the rewrite voltage increases with the number of rewrites. FIG. 3 is a characteristic diagram of the number of rewrites and the time of the present invention. This shows that the increase in the rewriting time is minimized even if the number of times is increased.

This makes it possible to prevent the rewriting time from increasing due to the number of rewritings. The correlation between the number of rewrites and the rewrite voltage is stored as a table in the ROM according to the process and the rewrite method. Conventionally, if such a determination circuit is incorporated in a non-volatile memory, the increase in area is a bottleneck, and it cannot be easily adopted. However, the above control can avoid the increase in area if processed by a microcomputer.

[0014]

As described above, the present invention provides a product that minimizes fluctuations in the rewriting time by changing the rewriting voltage built in the microcomputer and changing the rewriting frequency of the mounted nonvolatile memory. It is.

[Brief description of the drawings]

FIG. 1 is a block diagram of a microcomputer with a built-in nonvolatile memory according to the present invention.

FIG. 2 is a characteristic diagram of a rewrite frequency and a rewrite voltage according to the present invention.

FIG. 3 is a characteristic diagram of the number of rewrites and the rewrite time according to the present invention.

FIG. 4 is a block diagram of a conventional microcomputer with built-in nonvolatile memory.

FIG. 5 is a characteristic diagram of the number of times of rewriting and rewriting time of a conventional microcomputer with built-in nonvolatile memory.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microcomputer 2 Memory cell array 3 Voltage variable register 5 Rewriting voltage generation circuit 6 Rewriting voltage 201 Rewriting circuit storage 401 Switch 1 402 Switch 2 403 Switch 3

Claims (3)

[Claims] 1. A nonvolatile memory characterized in that the number of times of rewriting is updated and the number of times of rewriting is stored in the memory every time the nonvolatile memory is rewritten. 2. The nonvolatile memory according to claim 1, wherein the number of times of rewriting of the nonvolatile memory is determined, and the rewriting voltage is varied according to the number of times of rewriting. 3. A microcomputer comprising a nonvolatile memory, wherein the number of rewrites is stored in the nonvolatile memory, and a rewrite voltage is varied according to the number of rewrites.