Automatic Substitution of Faulty EPROM
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
In electrically programmable read-only memory (EPROM) modules having excess storage capacity, a functional block of storage locations can be automatically substituted for a faulty block after installation on a circuit card. Assume, for example, that a card has 64 kilobytes of EPROM memory but that only 40K are required, leaving three 8K blocks unused. When a storage module is tested, a digital quality stamp is written in bit positions 1-7 of the last storage location of the 64K EPROM. For instance, 01111100 represents that the first five 8K storage blocks are good. If one of the first five 8K blocks has a defective storage location, the stamp is modified to indicate that the faulty block has been replaced with one of two spare blocks. The designation for a faulty fourth block would be 01110110.