Abstract:
A control method for a radio frequency identification (RFID) tag is provided. The control method includes steps of prompting a plurality of RFID tags to enter a ready state; enabling a first RFID tag from the RFID tags to enter an accessible stage, and providing a first identification code to the first RFID tag; and commanding the first RFID tag to enter a standby state from the accessible stage.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATION 
     This patent application is based on Taiwan, R.O.C. patent application No. 97135026 filed on Sep. 12, 2008. 
     FIELD OF THE INVENTION 
     The present invention relates to a control method for a radio frequency identification (RFID) tag and an RFID system thereof, and more particularly, to a control method for a class 1 generation 2 (C1G2) compliant RFID tag and an RFID system thereof. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  is a schematic diagram showing a state flow of a C1G2 compliant RFID tag in the prior art. The RFID tag is controlled by an RFID reader to enter different states. A plurality of states, namely a ready state, an arbitrate state, a reply state, an acknowledged state, an open state, a secured state and a killed state, are illustrated in  FIG. 1 . In the ready state, supposing the RFID tag is a passive RFID tag, it means that the RFID tag receives signals transmitted by the RFID reader and thus generates power. The RFID tag then receives a command of the RFID reader and enters the arbitrate state. A time-consuming and complex singulation procedure is necessarily performed to allow one selected RFID tag at a time to enter other states after the reply state, while other RFID tags await in the arbitrate state. In the acknowledged state, the RFID reader sends an identification code, such as “handle” in this example, for identification when the RFID reader accesses data. 
     Generally speaking, the ready, arbitrate, reply, and acknowledged phases are preparatory steps for accessing the RFID tag. After the open state and the secured state, the RFID tag enters an accessible stage including the open and secured states. In the open state, a part of a data stored in a first RFID tag is accessible. In the secured state, the RFID reader need be authorized by the first RFID tag before accessing more data than in an open state; that is, secured data is then accessible provided the RFID reader is authorized. Once having entered the killed state, the RFID tag remains in the killed state, in which the RFID tag is inaccessible. Referring to  FIG. 1 , the RFID tag directly enters the killed state from the open state by skipping the secured state. Detailed operations of accessing other C1G2 compliant RFID tags are known to a person having ordinary skill in the art, and thus shall not be discussed for brevity. 
     However, within a same round of accessing a group of RFID tags, the accessed RFID tags cannot be accessed again until the entire state flow is repeated. When data of another RFID tag is needed for accessing one of the RFID tags, the entire state flow is executed to access the RFID tag, and the accessed data is temporarily stored in other memory apparatuses. Again, the entire state flow is repeated to access a data of another apparatus when needed. Such methodology is rather inconvenient. 
     SUMMARY OF THE INVENTION 
     Therefore, one objective of the present invention is to provide a control method for an RFID tag and a system thereof, so as to access the RFID tag without repeating the entire state flow as described above. 
     A control method for an RFID tag is provided according to an embodiment of the present invention. The control method comprises steps of prompting a plurality of RFID tags to enter a ready state, enabling a first RFID tag of the plurality of RFID tags to enter an accessible stage and providing a first identification code to the first RFID tag, and commanding the first RFID tag to enter a standby state from the accessible stage. 
     An RFID system using the foregoing method is provided according to another embodiment of the present invention. The RFID system comprises a plurality of RFID tags and an RFID reader. The RFID reader prompts the plurality of RFID tags to enter a ready state, enables a first RFID tag of the plurality of RFID tags to enter an accessible stage, provides a first identification code to the first RFID tag, and commands the first RFID tag to enter a standby state from the accessible stage. 
     With the above embodiments, the RFID tag is allowed to stay in a standby state, from which the RFID tag can be called out whenever needed, so that data access of the RFID tag is made more flexible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of accessing a C1G2 compliant RFID tag of the prior art; 
         FIG. 2  is a schematic diagram showing a C1G2 compliant RFID tag entering a standby state in accordance with an embodiment of the present invention; 
         FIG. 3  is a flow chart showing partial steps of controlling an RFID tag in accordance with an embodiment of the present invention; and 
         FIG. 4  is a flow chart showing partial of steps of controlling an RFID tag in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  is a schematic diagram showing a C1G2 compliant RFID tag entering a standby state in accordance with one embodiment of the present invention. Also with reference to  FIG. 1  for a better understanding of the present invention, only partial steps are illustrated for brevity. Referring to  FIG. 2 , the RFID tag enters a standby state after undergoing an accessible stage, which includes an open state and a secured state. Moreover, more than one RFID tag at a time is allowed to enter the standby state. In the standby state, an identification code ID different from an identification code handle is provided to the RFID tag. The identification code handle differs from the identification code ID in that, the identification code handle is provided in an acknowledged state to identify which RFID tag is to be accessed, whereas the identification code ID is provided to identify all the RFID tags in the standby state. For example, when five RFID tags enter the standby state, identification codes ID  1  to ID  5  are respectively designated to the five RFID tags, so as to precisely identify the RFID tags called out from the standby state. It is to be noted that the RFID tag need not be necessarily designated with respective identification codes ID. The identification code ID is to ensure that the RFID tag in the standby state is accessed more smoothly. It is feasible to apply the identification code handle, instead of the identification code ID, for identifying all the RFID tags in the standby state. However, proper modifications may be made such as applying other methods to identify RFID tags, as also encompassed within scope of the present invention. For example, the identification code ID and the identification code handle are used simultaneously to ensure correctness of identification. 
     The RFID tag having entered the standby state may remain in the standby state. When called out from the standby state, the RFID tag may enter to the open or secured state without returning to the ready state, the arbitrate state, the acknowledged state, and the reply state illustrated in  FIG. 1 , i.e., the RFID tag directly enters to the accessible stage and can then be directly accessed. Furthermore, when the RFID tag exits from the standby state, the RFID tag, which need not return to the open or secured state, receives a command, e.g., in the embodiment, a SNAK command for resetting the RFID tag to the ready state, and accordingly re-enters the ready state. 
     The disadvantage in the prior art that the entire state flow must be repeated to again access a data of the RFID tag is overcome via the foregoing method. Consider accessing two RFID tags, for example, to clearly illustrate an operation of the present invention. A first RFID tag, such as a passive RFID tag in the embodiment, is powered by an RFID reader to enter the ready state. After the arbitrate state, the reply state and the acknowledged state, the first RFID tag is provided with an identification code handle and enters an open or a secured state; that is, the RFID tag enters an accessible stage. When a second RFID tag is to be accessed, the first RFID tag first needs to enter a standby state. As mentioned above, when the first RFID tag enters the standby state, the RFID reader simultaneously provides another identification code ID different from the identification code handle to the first RFID tag. The identification code ID is for identifying the first RFID tag in the standby state. Alternatively, the RFID reader may provide only the identification handle but not the identification code ID to the first RFID tag to achieve a same objective. 
     When the first RFID tag enters the standby state, the RFID reader prompts the second RFID tag to enter a conventional state flow including a ready state, an arbitrate state, a reply state, an acknowledged state, an open state or a secured state. When data of the second RFID tag is accessed, the second RFID tag enters a standby state. The first RFID tag is then called out from the standby state to the open state or the secured state, from which data of the first RFID tag is accessed. Therefore, according to the foregoing method, one or a plurality of RFID tags are made to enter the standby state as needed to increase the applicability of data access of RFID tags. 
       FIG. 3  and  FIG. 4  are flow charts of partial steps of controlling an RFID tag in accordance with an embodiment of the present invention. It is to be noted that the illustrated steps represent only an example and shall, accordingly, not be construed as limiting. Referring to  FIG. 3 , suppose the RFID tag is in an open state or a secured state to subsequently enter a standby state. In Step  301 , the RFID tag is in the open state or the secured state. In Step  303 , the state of the RFID tag is recorded. More specifically, whether the RFID tag is at the open state or the secured state is recorded, so that the RFID tag can return to the recorded state after exiting from the standby state. Step  305  of receiving a command is then executed. In Step  307 , whether the command is a signal command is determined. The signal command is for calling out the RFID tag from the standby state to an accessible stage, which may be the open state or the secured state. Therefore, when the RFID tag receives the command while not being in the standby state, the command is considered as improper. The RFID tag is then forced back to the ready state. When the command is not a signal command, Step  309  of determining whether the command is the standby state command is executed. The method proceeds to Step  311  when the command is a standby state command, or else proceeds to Step  319  when the command is not a standby state command. In Step  319 , the method follows other instructions to comply with the C1G2 specifications. In Step  311 , whether an identification code handle contained in the command is the same as an identification code handle of the RFID tag is determined. That is, whether the command is received by a correct RFID tag is determined. When the result is negative, Step  317  of returning to the ready state is executed; otherwise, Step  313  of providing an identification code ID is executed. Whether to execute the optional Step  313  is determined according to a practical need to provide better design flexibility. In Step  315 , the RFID tag enters the standby state. 
     Referring to  FIG. 4 , suppose the RFID tag is in a standby state to subsequently exit from the standby state. In Step  401 , the RFID tag is in the standby state. In Step  403 , the RFID tag receives a command. In Step  405 , whether the command is a SNAK command for resetting the RFID tag to the ready state is determined. That is, whether to prompt the RFID tag to exit the standby state to return to the ready state is determined. When the received command is a SNAK command, Step  406  of returning to the ready state is executed; otherwise, Step  407  of determining whether the command is a standby state command is executed. When the received command is a standby state command, it means that the RFID tag shall not exit from the standby state, and hence Step  408  of remaining in the standby state is executed; otherwise, Step of  409  determining whether the command is a signal command is executed. The signal command is for calling the RFID tag out from the standby state to return to an accessible stage. When the received command is a signal command, Step  411  is executed; otherwise, Step  408  is executed. In Step  411 , whether an identification code handle contained in the command is the same as an identification code handle of the RFID tag is determined. That is, whether the command is received by a correct RFID tag is determined. When the two identification codes match, Step  413  is executed; otherwise, Step  408  is repeated. In Step  413 , whether an identification code ID contained in the command is the same as an identification code ID of the RFID tag is determined. When the two identification codes match, Step  415  is executed; otherwise, Step  408  is repeated. Similarly, the optional Step  415  is executed in conjunction with the optional Step  413 . That is, when the identification code ID is provided when the RFID tag enters the standby state from the accessible stage, Step  413  has to be executed. In Step  415 , whether the previously recorded state is the open state is determined. When the previously recorded state is the open state, Step  417  in which the RFID tag enters the open state is executed; otherwise, Step  419  in which the RFID tag enters the secured state is executed. 
     It is to be noted that, the embodiments take the RFID C1G2 specifications as an example. However, other specifications can be applied within the scope of the appended claims. From the foregoing description, the RFID tag is provided with an extra standby state in the accessible stage and enters the standby state when needed. Thus, in a single access cycle, when a specific RFID tag is accessed, even if other RFID tags are accessed, the specific RFID tag can be accessed again without executing the time-consuming and complex singulation procedure. Therefore, the inconvenience that an accessed RFID tag can only be again accessed in the next access cycle in the prior art is eliminated, so data access of the RFID tag is provided with better flexibility according to the present invention. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the above embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.