# US 8,786,408 B2 · Method for searching a plurality of RFID tags and apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,408 B2 - Document ID: US8786408B2 - Status: Granted - Kind: B2 - Application number: 12/651,778 - Filed: 2010-01-04 - Published: 2010-07-08 - Granted: 2014-07-22 - Earliest claimed: 2009-01-07 - Assignees: MStar Semiconductor, Inc. - Applicants: Chiung Hung Chang - Inventors: Chiung Hung Chang - Web page: https://patentgrep.com/patent/US8786408B2 ## CPC - G06K 7/0008: {General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer} - G06K 7/10019: {resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. (collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08)} - H04Q 2213/13003: Constructional details of switching devices - G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS - H04Q: SELECTING (switches, relays, selectors H01H; wireless communication networks H04W) ## Abstract A method for searching RFID tags and an RFID reader thereof are provided. Each of a plurality of RFID tags awaiting to be accessed has a UID composed of a plurality of bits. The method comprises dividing the plurality of bits of the UID into groups to generate a plurality of groups; selecting a first group and a first value for the first group; obtaining a search result according to a search command and the UIDs of the RFID tags; and analyzing the search result to determine whether at least one RFID tag corresponds to the first group and the first value. Each of the groups has n bits, where n is a positive integer greater than or equal to 1. ## Claims ### Claim 1 An RFID reader, for searching a plurality of RFID tags each having an UID composed of a plurality of bits, the RFID reader comprising: a control unit configured to divide the plurality of bits into a plurality of groups each having n bits, and select a first group from the groups and a first value for the first group, wherein n is a positive integer greater than 1; a communication protocol processing module, coupled to the control unit, configured to generate a search command according to the first group and the first value, wherein the RFID reader obtains a search result according to the search command and the UIDs of the RFID tags; and an analyzing module, coupled to the communication protocol processing module and the control unit, configured to generate a control signal to control the control unit of the RFID reader, and further configured to analyze the search result to determine whether at least one RFID tag corresponds to the first group and the first value, the analyzing module further configured to: generate the control signal having a first value in response to the search result indicating a collision due to more than one response from the RFID tags happens such that, according to the control signal, the control unit selects a group other than the first group from the groups, and generate the control signal having a second value in response to the search result indicating a response from one of the RFID tags such that, according to the control signal, the control unit selects a value different from the first value for the first group. ### Claim 2 (depends on 1) The RFID reader as claimed in claim 1, wherein the first group is one group, among the groups, having a most significant bit or a least significant bit of the plurality of bits. ### Claim 3 (depends on 1) The RFID reader as claimed in claim 1, wherein the first value is in a range from 0 to 2n−1, and wherein the control unit selects the first value according to a first predetermined sequence so that all values within the range can be selected. ### Claim 4 (depends on 3) The RFID reader as claimed in claim 3, wherein, when the search result indicates that the collision happens, the analyzing module records the first value when the collision happens and generates the control signal. ### Claim 5 (depends on 4) The RFID reader as claimed in claim 4, wherein the control unit increments or decrements the first value according to the control signal and the first predetermined sequence, selects a second group from the groups according to the control signal and a second predetermined sequence, and selects a second value for the second group. ### Claim 6 (depends on 5) The RFID reader as claimed in claim 5, wherein the second value is in a range from 0 to 2n−1, and wherein the control unit selects the first group and the first value again when the control unit further determines all values for the second value in the range have been selected. ### Claim 7 (depends on 3) The RFID reader as claimed in claim 3, wherein, when the search result indicates that no reply is generated, the analyzing module generates the control signal having a third value, and wherein the control unit increments or decrements the first value according to the control signal and the first predetermined sequence. ### Claim 8 (depends on 3) The RFID reader as claimed in claim 3, wherein, when the search result indicates that a reply is generated and no collision happens, the analyzing module records the reply and generates the control signal. ### Claim 9 (depends on 8) The RFID reader as claimed in claim 8, wherein the control unit increments or decrements the first value according to the control signal and the first predetermined sequence. ### Claim 10 (depends on 1) The RFID reader as claimed in claim 1, wherein the control unit ends a search procedure when the control unit further determines a value represented by n bits of the first group has been searched. ### Claim 11 A method for searching a plurality of RFID tags each having a UID composed of a plurality of bits, the method comprising: dividing, by a control unit of an RFID reader, the bits into a plurality of groups each having n bits, wherein n is a positive integer greater than or equal to 1; selecting, by the control unit, a first group of the groups and a first value for the first group; generating, by a communication protocol processing module of the RFID reader, a search command according to the first group and the first value, wherein a search result is obtained according to the search command and UIDs of the RFID tags; analyzing, by an analyzing module of the RFID reader, the search result to determine whether at least one RFID tag corresponds to the first group and the first value; generating, by the analyzing module, a control signal to control the control unit of the RFID reader, the control signal having a first value in response to the search result indicating a collision due to more than one response from the RFID tags happens, such that the control unit selects a group other than the first group from the groups; and generating, by the analyzing module, the control signal to control the control unit of the RFID reader, the control signal having a second value in response to the search result indicating a response from one of the RFID tags, such that the control unit selects a value different from the first value for the first group. ### Claim 12 (depends on 11) The method as claimed in claim 11, wherein the first group is one group, among the groups, having a most significant bit or a least significant bit of the plurality of bits. ### Claim 13 (depends on 11) The method as claimed in claim 11, wherein the first value is in a range from 0 to 2n−1, and wherein selecting the first value comprises selecting the first value according to a first predetermined sequence so that all values within the range can be selected. ### Claim 14 (depends on 13) The method as claimed in claim 13, further comprising: when the search result indicates that a collision happens, recording the first value when the collision happens and generating the control signal. ### Claim 15 (depends on 14) The method as claimed in claim 14, further comprising: changing the first value according to the control signal and the first predetermined sequence; selecting a second group of the groups according to the control signal and a second predetermined sequence; and selecting a second value for the second group. ### Claim 16 (depends on 15) The method as claimed in claim 15, further comprising: selecting the first group and the first value again when it is determined the second value has been selected. ### Claim 17 (depends on 13) The method as claimed in claim 13, further comprising: generating the control signal having a third value when the search result indicates that no reply is generated; and changing the first value according to the control signal and the first predetermined sequence. ### Claim 18 (depends on 13) The method as claimed in claim 13, further comprising: recording a reply and generating the control signal when the search result indicates that the reply is generated and no collision happens; and changing the first value according to the control signal and the first predetermined sequence. ### Claim 19 (depends on 11) The method as claimed in claim 11, further comprising: ending a search procedure when it is determined a value represented by n bits of the first group has been searched.