To provide a demodulation circuit for a BPSK (binary phase shift keying) signal realized as a contactless IC card reader/writer that can accurately recognize response signals from a plurality of IC cards.
The operation of the IC card reader/writer includes: step S11 for transmitting a data stream for initial response; step S13 for judging the occurrence of a collision when a response data stream is received in step S12, and returning to the step S11 again on the occurrence of a collision; step S14 for activating required IC cards among the IC cards that are individually recognized in this step when no collision takes place and transmitting a command data stream to bring a HALT state to the IC cards that are not required; and steps S15, S16 for transmitting the data stream for initial response similarly to the case with the steps S11, S12 again, and discriminating whether the response data stream is to be received. Thus, this method can reliably recognize the plurality of IC cards even when the energy for transporting the response data stream differs due to the difference of distance or the like.
COPYRIGHT: (C)2004,JPO
Hiromasa Yamaguchi
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Ryuichi Kijima
Toru Enya
Ichiro Kaneko