Patent ID: 7590793

Claim:
An access control method comprising: providing a flash memory, which comprises a set of a plurality of blocks, each of which has at least one data area and a flag area; referring to flag data written in said flag area of each of said plurality of blocks, to determine whether one of said plurality of blocks is valid; reading out data from said block when it is determined based on said flag data that said block is valid; wherein said flag area comprises a valid flag area and an invalid flag area separate from said valid flag area, and wherein the flash memory is initially written with valid data in at least one of a plurality of blocks, wherein said referring step comprises: reading out said flag data from said valid flag area and said invalid flag area in each of said plurality of blocks; and carrying out a first determination of whether said block is valid, based on said read out flag data from said valid and invalid flag areas in each of said plurality of blocks; setting a voltage for said flash memory to a read voltage level before said step of reading out said data from said valid and invalid flag areas; setting the voltage for said flash memory to a write voltage level, when said valid data is written in said valid flag area of said first block and said invalid data is not written in said invalid flag area of said first block and when said valid data is written in said valid flag area of said second block and said invalid data is not written in said invalid flag area of said second block; reading out said flag data from said valid and invalid flag areas in each of said plurality of blocks, after said step of setting the voltage for said flash memory to the write voltage level; and carrying out a second determination of whether said first block or said second block is valid, based on said read out flag data from said valid and invalid flag areas in each of said plurality of blocks.