Multiple Item Radio Frequency Tag Identification Protocol

A system for reading information from a plurality of radio frequency tags that are in the field of a radio frequency signal sent by a reader, comprising:

• i. a tag, further comprising:
• a. an antenna and tag radio frequency circuit for sending and receiving radio frequency signals to and from the reader;
• b. a tag memory for storing tag data;
• c. a tag logic circuit connected to the tag radio frequency circuit and the tag memory, the tag logic circuit having a tag state register that indicates the tag is in a state that is one of the states including READY, ID, and Data Exchange, the tag logic further having a state counter and a random number generator;
• and
• d. a tag algorithm, run by the tag logic;
• ii. a reader that is able to transmit information commands to the field of tags, the information commands including a Group_select, a Fail, and a Resend command,
• a. the Group_select command causing the tag algorithm to place one or more selected tags in the ID state by causing each selected tag algorithm to set its respective state register to ID and reset its respective state counter to a predetermined value,
• b. the Fail command being generated by the reader when more than one tag sends tag identification information to the reader simultaneously, the Fail command causing the algorithm of each selected tag to increment its respective state counter if:
• 1) the state counter has a value not equal to a predetermined value, or
• 2) the state counter has a value equal to the predetermined value and the random number generator has a given value,
• c. the Resend command sent by the reader when tag identification information is sent back to the reader in response to a READ command by a single tag in the field, the Resend command causing the state counter of all the tags in the field to decrement,
• whereby the reader can identify an individual tag in the field of tags, and cause the identified tag to go into a Data_Exchange state where the reader can access information from the tag memory.

A method, for reading a radio frequency identification tag in a radio frequency field of a plurality of tags comprising the steps of:

• a. sending a group_select command from a reader that places one or more selected tags in the field in a ID state;
• b. sending identification information from all the selected tags to the reader;
• c. sending a fail command from the reader if more than one tag sends identification information simultaneously;
• d. increasing a state counter value in the state counter of one or more selected tags if:
• 1) the state counter has a value not equal to a predetermined value, or
• 2) the state counter has a value equal to the predetermined value and the random number generator has a given value, the tag stopping transmission of the tag identification information while the state counter value is not equal to the predetermined value and the tag algorithm causing the random number generator to generate a new random value;
• e. sending identification information a next time from all the selected tags to the reader, the selected tags having a state counter value equal to the predetermined value;
• f. repeating steps c-e until a sole tag is sending identification information to the reader;
• g. issuing a READ command to the sole tag using the identification information of the sole tag;
• and
• h. placing the sole tag in a Data_exchange state where the reader can access data from the sole tag memory by using application commands.

A system for selecting a subset of slaves that satisfy a selection criterion, and causing the selected subset of slaves to participate in an identification and isolation process whereby slaves of the selected subset are successively identified and isolated from further participation in such identification and isolation process, said system comprising:

• (a) a master unit for communicating a command containing a selection criterion to a plurality of slaves;
• (b) each slave of said plurality of slaves being in one of three or more different possible conditions during the identification and isolation process;
• (c) a memory in said each slave containing at least one information value for use in evaluation of a selection criterion;
• (d) a receiving unit in said each slave for receiving the command containing the selection criterion from the master unit;
• and
• (e) a processing unit in said each slave that processes the command containing the selection criterion from the master unit;
• (f) the processing units of the slaves having a mode of operation such that a subgroup of slaves that have an information value that satisfies the selection criterion are moved from a first condition to a second condition for participation in an identification and isolation process;
• and
• (g) the processing units of the subgroup of slaves in the second condition having a mode of operation whereby individual slaves of said subgroup can progress to a third condition during the identification and isolation process, with slaves that have progressed to the third condition, and have been identified, being isolated from further participation in the identification and isolation process that continues so as to identify and isolate other of the slaves in the second condition.

A method for selecting a subset of slaves that satisfy at least one selection criterion during a selection process, and then identifying slaves of the selected subset, and causing identified slaves of the selected subset of slaves to be isolated from further participation in the identification process, said method comprising;

• (a) storing at least one information value in each of a plurality of slaves for use in evaluating at least one selection criterion;
• (b) representing at least one selection criterion in at least one selection criterion command;
• (c) communhicating the at least one selection criterion command to the plurality of slaves;
• (d) processing the at least one selection criterion command at each of said plurality of slave and deeming certain of the slaves based on storage of the at least one information value to be selected as a result of the selection process;
• (e) carrying out an identification process with respect to the certain slaves deemed selected as a result of the selection process;
• and
• (f) causing slaves that are identified during the identification process of clause (e) to be isolated trom responding farther in the course of the identification process of clause (e).