DATA CARRIER APPARATUS, COMMUNICATION SYSTEM, AND REPLACEABLE UNIT

In a data carrier apparatus, a reception unit receives, from a data carrier driving apparatus, a pulse signal that alternatingly repeats a first-level period and a second-level period, which are set based on individual data values. A measurement unit measures respective time widths of the first-level period and the second-level period in the received pulse signal. A demodulation unit demodulates data conveyed by the received pulse signal, by determining the data value corresponding to the first-level period based on a measured value of the first-level period output from the measurement unit and a first reference value, and determining the data value corresponding to the second-level period based on a measured value of the second-level period output from the measurement unit and a second reference value.