Semiconductor memory device and write control method therefor

Abstract

Disclosed is a semiconductor memory device which includes a read data latch that holds read data from a phase change memory and latches write data entered from outside and holds write data entered from outside, a write data latch that holds the write data for a cell for the time duration of a preset number of cycles until start of data write, a transfer switch that controls whether or not an output of the read data latch is to be transferred to the write data latch, a comparator circuit that decides whether or not data transferred to the write data latch via the transfer switch and held in the write data latch and data in the read data latch are coincident with each other, and a write flag latch that latches an output of the comparator circuit. Data is written only in case there is a write request and the result of comparison of the comparator circuit indicates non-coincidence, that is, only in bits in need of data writing.