Method of reading a plurality of non-contact data carriers, including an anti-collision scheme
View Patent ↗In a method of inventorying data carriers by means of a communication station, whereby the communication station and each data carrier are brought into communicative connection, and each data carrier brought into communicative connection with the communication station is capable of generating a response signal that renders possible an inventorying of the data carrier and is capable of delivering a generated response signal with the use of a transmission start moment that can be selected from a plurality of transmission start moments, each data carrier tests whether another data carrier is already giving its response signal. Each data carrier subsequently discontinues the generation or delivery of its response signal if another data carrier is already providing its response signal.
1. A method of inventorying data carriers by means of a communication station comprising:
choosing from a plurality of transmission start moments in reference to a start point in time a transmission start moment for starting a transmission of a carrier signal for the purpose of supplying data to a communication station during the transmission of said carrier signal, such that the data enable the inventory of the data carrier;
detecting whether another data carrier is already transmitting a carrier signal after said start point in time and prior to said chosen transmission start point, the detection comprising recognizing modulated coded commands and demodulating the modulated coded commands; and
inhibiting the starting of said transmission of said carrier signal at said chosen transmission start moment if a result of said detecting is positive;
starting the transmission of said carrier signal at the chosen transmission start moment if said result is negative;
maintaining during the carrier signal transmission a data free pre-data supply period in time before the supply of data takes place; and
maintaining during said carrier signal transmission a data free post-data supply period in time after the supply of data took place until the end of the carrier signal transmission.
2. A method as claimed in claim 1 wherein the transmission start moment is selected randomly.
3. A method as claimed in claim 1 wherein said choosing of said start moment allows the number of choose-able transmission start moments to be greater than the number of data carriers.
4. A method as claimed in claim 1 wherein said choosing of the transmission start moment is performed such that said start point in time is defined as the end of a carrier signal transmission of the communication station, the communication station being supplied its data representing an inventory command during its carrier signal transmission.
5. A method as claimed in claim 4 , wherein said choosing of the transmission start moment comprises shifting said transmission start moment in time by a selectable discrete delay period with respect to said end of the carrier signal transmission of the communication station.
6. A method as claimed in claim 1 , comprising setting said data carrier that supplied its data as identification data into an idle state by the communication station, in which idle state no carrier signal is transmitted.