JPH04182996A - Data erasable rom - Google Patents

Abstract

PURPOSE:To avoid erroneous writing or another data again by an operation error, etc., by setting the content indicating writing inhibition in a writing inhibition state memory circuit. CONSTITUTION:A writing inhibition control circuit 2 outputs a writing inhibition control signal to a writing inhibition circuit 3 in accordance with the information stored in the writing inhibition state memory circuit 1. The writing inhibition circuit 3 disconnects a voltage line 10 for writing from a chip control circuit 4 to prevent the arrival of a voltage for writing at a memory cell 7 by the control signal from the writing inhibition control circuit 2. The information on the writing inhibition of the writing inhibition state memory circuit 1 is erased together with the data stored in the memory cell 7 and a write enable state is attained when the ROM is irradiated with UV rays in the case of execution of rewriting. The writing of the data in this state is then possible. The erroneous writing of another data again is averted when the writing is executed once.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention provides a data erasable device capable of erasing data by irradiating ultraviolet rays or applying voltage.
Regarding OM.

(Prior Art) Conventionally, data can be erased by irradiating ultraviolet rays or applying voltage.
OM (EPROM, EEPROM) is provided, but when writing, there is no write-protection function, so make sure that data has not already been written and that important data has not been written. I had to write it later.

(Problems to be Solved by the Invention) As mentioned above, conventional data erasable ROMs do not have a write protection function, so if data is written once, there is a risk that different data may be written again by mistake. There is,
There is a problem in that not only the previous data is destroyed, but also the data cannot be written correctly because the previous data remains.

The present invention was made to eliminate such conventional drawbacks, and by providing a write protection function,
It is an object of the present invention to provide a data erasable ROM that can prevent double writing of data due to operational errors or the like.

[Structure of the Invention] (Means for Solving the Problems) The present invention, which achieves the above-mentioned conventional objects, provides an R
The OM includes a write inhibit circuit that inhibits writing, a write inhibit control circuit that controls the write inhibit circuit, and a write inhibit state storage circuit that stores information as to whether or not writing is prohibited, and the write inhibit control circuit that controls the write inhibit control circuit. The circuit controls the write-protection circuit based on information set in the write-protection state storage circuit to put it in a write-protection or write-enabled state, and the write-protection state storage circuit controls the write-protection state by irradiating ultraviolet rays or applying voltage. It is characterized in that when the data is erased, the stored write-inhibited information is also erased.

(Function) In the present invention, the write state is normally set, and writing is prohibited by setting content indicating write prohibition in the write inhibit state storage circuit. Further, when the write state storage circuit is irradiated with ultraviolet light, the memory of the write prohibited state is erased and the state is changed to a state indicating write permission. The ultraviolet irradiation performed during corner writing automatically enables writing at the same time as data erasing, so the user does not have to voluntarily enable writing.

As described above, it is possible to reliably prevent double writing of data due to operational errors or the like.

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

FIG. 1 is a block diagram showing the circuit configuration of an EP ROM according to an embodiment of the present invention.

In the figure, 1 is a write-inhibited state storage circuit that stores information on whether to prohibit or enable writing; 2 is a write-inhibited control circuit that controls write-inhibited operation according to the information content of the write-inhibited state storage circuit 1; 3 is a write inhibit circuit that inhibits or permits writing under the control of the write inhibit control circuit 2; 4 is a chip control circuit that performs overall control; 5 is an address buffer that amplifies the address signal; and 6 is a data buffer that amplifies the data signal. , 7 are memory cells for storing data.

A data protection line 11 is connected to the write-inhibited state storage circuit 1, and by activating this data protection line 11, information indicating that data writing is prohibited is stored. In addition, this write-inhibited state storage circuit 1
The write-protected information stored in ROM 1. : When irradiated with ultraviolet light, it is erased and becomes a memory state where writing is permitted. The write inhibit circuit 3 connects the write voltage line 10 to the chip control circuit 4 side to enable writing, and disconnects the write voltage line 10 from the chip control circuit 4 to inhibit writing. The write-inhibit control circuit 2 operates the write-inhibit circuit 3 according to the stored contents of the write-inhibit state storage circuit to enable or prohibit writing.

Next, the operation of the present EP ROM configured as described above will be explained.

In a normal state, the write-inhibited state storage circuit 1 stores information indicating that it is writable, and sets the memory self to a writable state.

By activating the data protection line 11, information indicating that data writing is prohibited is stored in the write inhibit state storage circuit 1. Then, the write-inhibit control circuit 2 outputs a write-inhibit control signal to the write-inhibit circuit 3 based on the information stored in the write-inhibit letter@storage circuit 1. In response to a control signal from the write inhibit control circuit 2, the write inhibit circuit 3 disconnects the write voltage line 10 from the chip control circuit 4 to prevent the write voltage from reaching the memory self. In this way, in the write-inhibited state, the voltage for writing does not reach the memory self, so writing is reliably prohibited.

In addition, when rewriting, when irradiating ultraviolet rays, the write-inhibited information in the write-inhibited state storage circuit 1 will be erased along with the data stored in the memory self, and the write-inhibited state will be established, so data can be written as is. becomes possible. Therefore, when it is in a write-protected state, there is no need to intentionally change it to a write-enabled state.

By operating as described above, even if writing is performed once due to an operational error or the like, different data will not be written by mistake again.

In addition, in the above, the case where the present invention is applied to an E F ROM in which data can be erased by irradiation with ultraviolet rays is shown.
Needless to say, the present invention can be applied to an EEFROM in which data can be erased by applying a voltage.

[Effects of the Invention] As explained above, according to the data erasable ROM of the present invention, writing is prohibited by setting contents indicating write prohibition in the write inhibit state storage circuit, so that - degree write is prevented. If this is done, it will no longer be possible to write different data by mistake again due to an operational error or the like.

Further, when rewriting is to be performed, the data cannot be written until after the data has been erased, so there is no possibility that the data may not be written correctly because the previous data remains.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the circuit configuration of a ROM according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Write-protection state memory circuit, 2... Write-protection control circuit, 3... Write-protection circuit, 4... Chip control circuit, 5... Address buffer, 6... Data buffer, 7 ...Memory cell, 10...Writing voltage line, 11...Data protection line. Applicant Toshiba Corporation Representative Patent Attorney Sasa Suyama −

Claims (1)

[Claims] A ROM in which data can be erased by irradiating ultraviolet rays or applying a voltage, comprising: a write inhibit circuit that inhibits writing; a write inhibit control circuit that controls the write inhibit circuit; and a write inhibit circuit that inhibits writing. and a write-protection state storage circuit that stores information as to whether or not write is prohibited, and the write-protection control circuit controls the write-protection circuit based on information set in the write-protection state storage circuit to prevent writing. Data erasable, characterized in that the write inhibited or write enabled state is set, and the write inhibited state storage circuit erases the stored write inhibited information when the data is erased by irradiation of ultraviolet rays or application of voltage. ROM.