Patent ID: 6249850
Filing Date: 2001-06-19
Classification: G06F,G11C

Abstract:
A copying preventing method for a mask ROM having electrically programmable redundancy cells, comprising:a first step of, when a defect is caused in a memory cell array, electrically disconnecting a defective memory cell corresponding to an address of the defect from the memory cell array;a second stop of electrically writing the same data as data stored in the disconnected memory cell, into the redundancy cells;a third step of electrically writing the address of the defective memory cell into an address-storing memory cell;a fourth step of writing error data into non-use cells among the redundancy cells;a fifth step of attaching access inhibition addresses to the non-use cells in which the error data is written;a sixth step of, when the address of the defective memory cell written in the address-storing memory cell is accessed, outputting the data from said one of the redundancy cells in which the same data as the data stored in the disconnected memory cell is written; anda seventh step of, when the access inhibition address is accessed, outputting the error data from the corresponding redundancy cell.