JPH01243295A - Mask rom device - Google Patents

Abstract

PURPOSE:To rapidly change and correct write information by dividing a mask ROM cell into plural areas, substituting an EPROM for one of them, and using the substituted EPROM cell when it is desired to change a part of the write information in the mask ROM. CONSTITUTION:When it is needed to correct storage data in a certain block in a mask ROM device, a decode address signal 17 corresponding to an address signal 13 for the mask ROM device is inputted to a block switching circuit 31. The block switching circuit 31, when receiving the decode signal 17, selects a substitute EPROM33 to a readout opposite party, and reads out it as the storage content of the block necessary to correct a ROM memory matrix 18. Readout data 35 is outputted from a terminal 24 similarly in case of the mask ROM memory matrix 18 via a Y selector 21 and an output buffer 23. By such constitution, it is possible to change data written in the mask ROM rapidly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mask ROM device, and particularly to its circuit configuration.

[Conventional technology]

A mask ROM is a memory device in which stored information is burned and fixed during the LSI manufacturing process using a photolithography technique. In recent years, mask ROMs have been widely used in various information processing devices, such as office automation equipment, especially word processors, personal computers, and printers, and have become very important. Its performance and functions have been improving recently, especially its large capacity.
It is the most advanced among SI. This is largely due to the advancement of more sophisticated information processing equipment and the promotion of higher quality display in Japanese processing such as kanji.

FIG. 2 shows this type of conventional mask ROM.

The information data in the mask ROM memory matrix 18 shown in the figure is burned by a mask during the mask ROM diffusion process, and is written in a form that cannot be modified any longer when the wafer is completed or packaged. There is. Reading of this written information is performed as follows.

First, the chip enable terminal 11 is brought into a selected state, and the address signal 13 is applied to the address terminal 12. This address signal 13 is the address human buffer latch 1
4 to the X decoder 15 and Y decoder 16.

Then, it is decoded by these χ and Y decoders 15 and 16 and sent to the mask ROM memory matrix 18 as a decode address signal 17. According to this decode address signal 17, the stored information 20 (one bit or multiple bits) is masked R by the Y selector 21.
OM memory memory) Selected from IJ wax 8. Then, it is read out to the output terminal 24 through the output sofa 23.

[Problem to be solved by the invention]

However, such conventional mask ROM devices have the following drawbacks. That is, although the product life of office equipment, printers, terminal equipment, etc. to which mask ROM devices are applied is short, there is a problem in that the lead time required for the development of mask ROM devices is about three months.

Further, the specifications of the above-mentioned devices change frequently and are often not decided until just before shipment.

In such a case, the contents of the ROM must be changed in accordance with changes in the specifications of the device, and this must be done quickly. Therefore, a single-use EPROM device may be considered, but this also has the following problems. In other words, compared to mask ROM, EP ROM is slightly slower in increasing its capacity, and is completely comparable to the most advanced mask ROM! Almost no EPROM that can replace this has been developed yet.

Therefore, the purpose of this invention is to divide the mask ROM cell into multiple areas, replace one of the areas with an EPROM cell, and use this alternative EPROM cell when you want to partially change the write information of the mask ROM. Mask R allows you to quickly change and modify the written information in the mask ROM.
Our objective is to provide an OM device.

[Failure to solve the problem]

The mask ROM device of the present invention has a mask ROM cell matrix divided into a plurality of memory blocks, and when it is desired to internally change any of the divided memory blocks, the stored contents of this block can be changed in advance to a substitute. The block of the mask ROM cell matrix and the alternative E
and a block switching circuit for switching and selecting PROM cells.

Therefore, when using the mask ROM device according to the present invention, when it is desired to change the information written in one of the blocks of the mask ROM device divided into a plurality of blocks, the change data is written in advance in the substitute EPROM cell. . When it is desired to read this changed data, a block switching circuit that checks an external address reads the contents of the alternative EPROM cell to the address that needs to be read.

〔Example〕

The present invention will be described in detail with reference to Examples below.

FIG. 1 shows the mask ROM device of this embodiment. Components that are the same as those in FIG. 2 are designated by the same reference numerals, and their description will be omitted as appropriate.

In the figure, the mask ROM memory matrix 18 is burned into the mask ROM memory matrix 18 using a mask in the diffusion process during mask ROM manufacturing, and is written as data that cannot be modified when the wafer is completed or packaged.

Data reading: Well, it is almost the same as the conventional example, and is performed as follows. After chip enable terminal 11 is brought into the selected state, address signal 13 is applied to address terminal 12. This address signal 13 is an address manual buffer.
It is sent via latch 14 to X and Y decoders 15.16. X decoder 1 receiving this address signal 13
5 decodes this and sends it as a decoded address signal 17 to the mask ROM memory matrix 18 and the block switching circuit 31 which is a feature of the present invention. Similarly, the Y decoder 16 also decodes the manually generated address signal 13 and outputs the decoded address signal 32 to the Y selector 2.
Send to 1. The block switching circuit 31 switches between each divided block of the mask ROM memory matrix 18 and an alternative EP ROM cell 33, which will be described below, according to external access information for the mask ROM device, that is, the address signal 13. , operate to select.

Block switching circuit 31 and alternative E, which are the characteristics of the present invention.
As already explained, the PROM cell 33 is used when it is desired to urgently change the contents of the mask ROM device. This is a very important issue for office automation equipment and printer terminal equipment, which have short product lifespans and short lead times for product development, and how quickly the contents of the mask ROM device can be changed is a matter of vital importance to device developers. It also becomes a problem.

When such a change occurs, it is usually rare that the entire mask ROM is internally changed, and only a certain limited area or block is modified in most cases. Therefore, it is checked in advance whether such an area or block is part of a mask ROM device5).
Modified data of the data stored in this area or block is written to the alternative EP ROIVI 33. The method of writing to this alternative EPR○M33 is the general EFR
This can be done in the same way as in the case of OM.

In this way, when it becomes necessary to modify the data stored in a certain block of the mask ROM device, the mask R
Address signal 13 which is access information for the OM device
A decode address signal 17 corresponding to the block switching circuit 31 is inputted manually. When the block switching circuit 31 receives this decode address signal 17, it selects the alternative EPROM 33 as the read partner, and does not read out the stored contents of the block that requires correction in the mask ROM memory matrix 18. The read data 35 is sent to the Y selector 21, as in the case of the mask ROM memory matrix 18.
It is output from the output terminal 24 via the output huffer 23.

In the above embodiment, an E PROiV] cell is also provided for the block switching circuit 31, and when an external address accesses the changed data area, the alternative E
A program may be stored in an EPROM cell to read the PROM 33.

〔Effect of the invention〕

As explained above, in the present invention, it is necessary to divide a mask ROM cell matrix into a plurality of memory blocks, provide an alternative EPROM cell with the same capacity as one of the blocks, and change the storage contents of one of the blocks. When changing data, replace the EPROM in advance! When writing and reading data, the block switching circuit reads out the contents stored in the alternative ROM, thereby making it possible to quickly change and modify the data written in the mask ROM device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the mask ROM device of the present invention, and FIG. 2 is a block diagram showing a conventional mask ROM device. 18...Mask ROM memory matrix, 3
1...Block switching circuit, 33...Alternative EPROM0

Claims (1)

[Claims] A mask ROM cell matrix is divided into a plurality of memory blocks, and when it is necessary to change the memory contents in any of the plurality of divided memory blocks, the stored contents of this block are written in advance as a replacement. Replacement EPROM cell to be stored and corresponding mask RO from outside
A mask ROM device comprising: a block switching circuit that switches and selects a block of the mask ROM cell matrix and the alternative EPROM cell according to access information to the M device.