Patent ID: 7011250

Claim:
A reader/writer for IC cards that communicates with a plurality of IC cards using time slots, comprising: a response-detection unit operable to detect normal responses from the IC cards, in response to an initial request for identifying each card, and collisions of the responses; a response-invalidation unit operable to send a response-invalidation command, which is a command not to respond to a future initial request, to the IC cards that sent normal responses when the response-detection unit received normal responses from the IC cards even though collisions were detected; a calculation unit operable to calculate a number of the time slots to be included in the future initial request for identifying each IC card based on whether or not the response-invalidation unit sent the response-invalidation command; and a slot-number-reset unit operable to set the number of time slots calculated by the calculation unit as the number of time slots for the future initial request.