Memory card device

Details Memory card device Memory card device

1994-04-08

1996-01-09

Zarabian, A.

Static information storage and retrieval

Read/write circuit

Bad bit

36523003, G11C 1140

Patent

active

054834910

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a memory card device using an EEPROM (Electrically Erasable and Programmable Read Only Memory) as a semiconductor memory and, more particularly, to a memory card device suitably used for an electronic still camera apparatus or the like for converting an optical image of a photographed object into digital image data and recording the image data in a semiconductor memory.


BACKGROUND ART

As is well-known, an electronic still camera apparatus for converting an optical image of a photographed object into an electrical image signal using a solid-state imaging device, converting the image signal into digital image data, and recording the data in a semiconductor memory, has been developed. In this type of electronic still camera apparatus, a memory card including a semiconductor memory in a card-like case is formed detachably from the body of the camera apparatus so that the memory card can be handled in the same way as a film of a normal camera is.
At present, the memory card of the electronic still camera apparatus is being standardized, and a large memory capacity semiconductor memory for recording a plurality of items of digital image data is required as the semiconductor memory included in the memory card. For example, an SRAM (Static Random Access Memory), a mask ROM, an EEPROM capable of electrically writing and erasing data, and the like are taken into consideration, and a memory card using the SRAM has been already commercialized.
While the memory card using the SRAM has advantages wherein it can be adapted to a data structure of whatever format and the data write/readout speed is high, it has drawbacks wherein a backup battery for holding the written data has to be put into the memory card and thus a memory capacity is reduced by the space for the backup battery and the cost of the SRAM itself is increased uneconomically.
In order to eliminate the drawbacks of the SRAM, the EEPROM has attracted attention as a semiconductor memory used in a memory card. More specifically, the EEPROM attracts attention as a recording medium in place of a magnetic disk, and has the advantages of requiring no backup batteries and decreasing the cost of a chip which are different from those of the SRAM. Therefore, the EEPROM is greatly improving in using as a memory card.
FIG. 1 shows the merits and demerits of a memory card using an SRAM (SRAM card) and a memory card using an EEPROM (EEPROM card). With respect to the backup battery of item 1 and the cost of item 2 in FIG. 1, as described above, the SRAM card has problems wherein it requires a backup battery and increases in cost, and the EEPROM card has advantages wherein it requires no backup batteries and reduced in cost.
The write speed of item 3 and the readout speed of item 4 each can be considered in two different modes one of which is a random access mode common to the SRAM and EEPROM in which data is written/read out to/from an arbitrary byte or bit designated by an address and the other of which is a page mode proper to the EEPROM in which a page having a plurality of successive bytes (several hundreds of bytes) is designated and data is written/read at once for each page.
In the random access mode, the write and read speeds of the SRAM are both high, while those of the EEPROM are both low. Since, in the page mode, the EEPROM writes/reads a large amount of data for one page at once, its data write/read speed is higher than in the random access mode.
The erase mode of item 5 is a mode proper to the EEPROM and not included in the SRAM. More specifically, when the EEPROM writes new data in a region including old data, that is, when the EEPROM rewrites data, it cannot write the new data unless the old data is erased. For this reason, the erase mode is executed when data is written.
The write verify of item 6 is also a mode proper to the EEPROM and not included in the SRAM. Since the EEPROM cannot write data completely by a single normal operation, it is necessary to check whether data is correctly written to the EEPROM by re

REFERENCES:
patent: 5278794 (1994-01-01), Tanaka
patent: 5303192 (1994-04-01), Baba

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