Memory system and method using ECC with flag bit to identify modified data

摘要

A DRAM device includes an ECC generator/checker that generates ECC syndromes corresponding to items of data stored in the DRAM device. The DRAM device also includes an ECC controller that causes the ECC syndromes to be stored in the DRAM device. The ECC controller also causes a flag bit having a first value to be stored in the DRAM device when a corresponding ECC syndrome is stored. The ECC controller changes the flag bit to a second value whenever the corresponding data bits are modified, this indicating that the stored syndrome no longer corresponds to the stored data. In such case, the ECC controller causes a new ECC syndrome to be generated and stored, and the corresponding flag bit is reset to the first value. The flag bits may be checked in this manner during a reduced power refresh to ensure that the stored syndromes correspond to the stored data.