Patent ID: 7086588

Claim:
A data communication system comprising: a reader/writer device; and an identification tag that communicates data with the reader/writer device, wherein: the reader/writer device has a first data communication section that communicates data with the identification tag; the identification tag has a second data communication section that communicates data with the reader/writer device, and a display section that displays based on data received by the second data communication section, and that retains a display content for a display retaining period after a drive voltage is applied to the display section for a drive voltage application time and while no drive voltage is applied to the display section; the identification tag is attached to at least one of a commodity and a commodity package; at least one of the drive voltage and the drive voltage application time are calculated based on a desired display retaining period that corresponds to a time limit of the commodity; and the display retaining period is controlled by the applied drive voltage and the drive voltage application time and corresponds to the desired display retaining period.