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EXTENDING THE LIFE OF SMART CARDS BY REALLOCATING FILES IN THE EEPROM

IP.com Disclosure Number: IPCOM000004682D
Original Publication Date: 2001-Apr-04
Included in the Prior Art Database: 2001-Apr-04
Document File: 1 page(s) / 5K

Publishing Venue

Motorola

Related People

Morris Bahrami: AUTHOR

Abstract

EXTENDING THE LIFE OF SMART CARDS BY REALLOCATING FILES IN THE EEPROM

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EXTENDING THE LIFE OF SMART CARDS BY REALLOCATING FILES IN THE EEPROM

by Morris Bahrami

Each memory location in the EEPROM can only be written into a finite number of times. Smart cards use the EEPROM to store certain information which gets updated and needs to be accessible during use. The method described here reallocates the files in the EEPROM which are frequently written into so that different locations in the EEPROM get updated more uniformly. This extends the number of times a file in a smart card can be written into and consequently extends the useful life of the smart card.

In the method described here, the smart card keeps two or more tables in the EEPROM which indicate how many times each file in the EEPROM has been written into. The entries for each file in the tables are initialized with 0. Each time a file gets written into, the counter entry in the selected table gets incremented.

If this number gets to a set limit (N) then the file is reallocated to another location in the EEPROM at the beginning of the smart card life cycle (Figure 1) and when a file has been written into for maximum (N) number of times (Figure 2).

When all of the unused sections of the EEPROM are used or the remaining free sections of the EEPROM are not large enough to contain a particular file that an attempt has been made to write into, the smart card gives a "EEPROM write exceeded" message back to the terminal that has tried to write that file.

The only section of the tables that gets updated is the "write counter", the locations for accessing files are fixed. Therefore only the write counter element of the tables needs to be in EEPROM and the rest can stay in ROM.

Figure 3 shows a flow diagram for the process of file reallocation in EEPROM for one file (File A). Other files will use a similar process. This example is for the case where there are only two tables (Table 1 and Table 2) which store the number of times a file has been written into. Depending on the EEPROM size and the number of files in the EEPOM, there can be many more tables.

[See the accompanying PDF file for the Figures]