Abstract:
Each data carrier of multiple data carriers is assigned a time slot within which to communicate with a base station. The base station allocates the time slots by acknowledging receipt of a data carrier&#39;s unique identifier during the assigned time slot. Each data carrier stores its assigned time slot, and communicates only when a time-slot counter indicates the occurrence of the assigned time slot.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The application is a continuation of application Ser. No. 09,325,675, filed Jun. 3, 1999, now U.S. Pat. No. 6,510,149. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The invention relates to a data carrier which is constructed for contactless communication with a station which is at least suitable for reading, and includes receiving means for receiving data blocks and transmission means for transmitting data blocks, and includes a circuit with a receiving terminal for receiving data blocks received by means of the receiving means and with a transmission terminal for outputting data blocks to be transmitted by means of the transmission means, and with time slot determination means which are arranged so as to determine each time slot of possibly repeatedly, successively running time slot sequences, each of which consists of a given number N of successive time slots, and with first processing means which are arranged to process a selection data block which is transmitted by a station in order to initiate a selection operation and is received via the receiving terminal and serves to select the data carrier from a plurality of data carriers, and with second processing means which are arranged to process, after the processing of a received selection data block by means of the first processing means, an identification data block which is stored in the circuit of the data carrier and can be applied, after its processing by means of the second processing means, during the duration of an nth time slot of a time slot sequence and via the transmission terminal, to the transmission means for transmission to a station, where 1≦n≦N, and with third processing means which are arranged to process, after correct reception in a station of an identification data block transmitted by the data carrier to this station, an acknowledge data block which is transmitted by this station to the data carrier and is received via the receiving terminal and is capable of setting the circuit of the data carrier to a selected state. 
     The invention also relates to a circuit which includes the following means, namely a receiving terminal for receiving received data blocks, and a transmission terminal for outputting data blocks to be transmitted, and time slot determination means which are arranged so as to determine each time slot of possibly repeatedly successively running time slot sequences, each of which consists of a given number N of successive time slots, and first processing means which are arranged to process a selection data block which is transmitted by a station, being at least suitable for reading, in order to initiate a selection operation and is received via the receiving terminal and serves to select the circuit from a plurality of circuits, and second processing means which are arranged to process, after the processing of a received selection data block by means of the first processing means, an identification data block which is stored in the circuit and can be applied, after its processing by means of the second processing means and during the duration of an n th  time slot of a time slot sequence, to the transmission terminal for transmission to a station, where 1≦n≦N, and third processing means which are arranged to process, after correct reception in a station of an identification data block transmitted by the circuit to this station, an acknowledge data block which is transmitted by this station to the circuit and is received via the receiving terminal and is capable of setting the circuit to a selected state. 
     2. Description of Related Art 
     A data carrier of the kind set forth in the first paragraph and a circuit for a data carrier of the kind set forth in the second paragraph are known, for example from the patent document U.S. Pat. No. 5,539,394 A. When a known data carrier of this kind is present, together with a plurality of similar data carriers, within the communication range of a station which is at least suitable for reading, a data carrier can be selected in each time slot during a selection operation where a time slot sequence is executed. During such a selection operation, each selected data carrier transmits its identification data block to the station so that after such a selection operation the station knows the identity of the data carriers selected in the course of the executed selection operation. Subsequently, the station can address each selected data carrier individually in order to execute at least one communication operation with each selected data carrier, for example a read operation or a write operation or another operation. 
     It is a drawback of the known data carrier that, after selection of a given number of such known data carriers, in order to carry out a communication operation each of the selected data carriers must be addressed by way of a separate instruction so as to activate the relevant communication operation. The individual addressing of each selected data carrier by means of a respective instruction leads to a comparatively long communication interval; this is detrimental considering the need for as fast as possible communication with an as large as possible number of data carriers. Furthermore, because of the individual addressing of each selected data carrier by way of a respective instruction, a station arranged to communicate with the selected data carriers must generate and transmit a number of instructions which corresponds to the number of selected data carriers and hence produce a number of modulation steps, proportional to the number of instructions, in a carrier signal which serves for the transmission of the instructions to the data carriers and is in this case amplitude modulated; consequently, comparatively high levels occur in the range of the side bands of the amplitude modulated carrier signal used to transmit the instructions; in many countries this gives rise to conflicts with the rules and regulations concerning radio interference or radio interference limits. 
     BRIEF SUMMARY OF INVENTION 
     It is an object of the invention to eliminate the described problems and to provide an improved data carrier of the kind set forth in the first paragraph as well as an improved circuit of the kind set forth in the second paragraph. In order to achieve this object, a data carrier of the kind set forth in the first paragraph according to the invention is characterized in that the circuit of the data carrier includes time slot fixation means by means of which fixation means, subsequent to the processing of the acknowledge data block by means of the third processing means, the respective n th  time slot of successively running time slot sequences can be fixed for the circuit of the data carrier, and that the circuit of the data carrier includes control means by means of which control means, after fixation of the circuit of the data carrier to the respective n th  time slot, communication between the data carrier and a station can be enabled only during the respective n th  time slot fixed for the circuit of the data carrier. 
     In order to achieve the described object, a circuit of the kind set forth in the second paragraph according to the invention is characterized in that the circuit is provided with time slot fixation means by means of which fixation means, subsequent to the processing of the acknowledge block by means of the third processing means, respective the n th  time slot of successively running time slot sequences can be fixed for the circuit, and that the circuit includes control means by means of which control means, after fixation of the circuit to the respective n th  time slot, communication between the circuit and a station can be enabled only during the respective n th  time slot fixed for the circuit. 
     Using only few means the steps according to the invention ensure in a simple manner that, after selection of a number of data carriers constructed according to the invention, the station intended for communication with the selected data carriers need generate and transmit only a single instruction in order to activate a desired communication operation with each of the selected data carriers; this instruction, being valid for all selected data carriers, ensures activation of the desired communication operation, subsequent to this instruction, during the time slot fixed for each of the selected data carriers. It is thus achieved that a single instruction for activating a communication operation suffices to carry out such a communication operation with each of the selected data carriers successively, resulting in a communication interval of optimum short length. Moreover, it is thus achieved that a modulated carrier signal which is transmitted by a station in order to transmit the instruction to the data carriers according to the invention includes only the modulation steps required for the transmission of this single instruction, so that only small level values occur in the range of the side bands of the modulated carrier signal and conflicts with rules and regulations concerning radio interference or radio interference limits are definitely avoided. 
     These and other aspects of the invention will be apparent from the embodiment described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be described in detail hereinafter with reference to an embodiment shown in the drawings; however, the invention is not restricted thereto. 
         FIG. 1  shows a block diagram of an in this context essential part of a write/read station for contactless communication with a data carrier according to the invention. 
         FIG. 2  shows, in the same way as  FIG. 1 , an in this context, essential part of a data carrier according to the invention. 
         FIG. 3  shows a flow chart illustrating the execution of a program in the write/read station shown in  FIG. 1 . 
         FIGS. 4A and 4B  show a flow chart illustrating the execution of a program in the data carrier shown in  FIG. 2 . 
         FIG. 5  shows a time diagram illustrating the temporal sequence of data blocks occurring in the course of a communication operation between the write/read station of  FIG. 1  and the data carrier of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a write/read station  1  which will be referred to hereinafter as the station  1  for the sake of brevity. The station  1  is arranged and constructed for communication with a plurality of data carriers  2 .  FIG. 2  shows such a data carrier  2 . 
     In respect of the communication between the station  1  and the data carriers  2  it is to be noted in advance that such communication takes place mainly in the form of data blocks DB, each data block DB consisting of a predetermined number of bytes, each byte consisting of a predetermined number of bits, being 8 bits in the present case. Instruction data blocks are to be transferred from the station  1  to the data carriers  2  in the course of a communication between the station  1  and the data carriers  2 ; the following instruction data blocks can be mentioned in this respect: a selection data block SDB, a read data block RDB, a write data block WDB, and a stop data block HDB. Furthermore, the station  1  can also transfer an acknowledge data block QDB to the data carriers  2 . The station  1  can also transfer further instruction data blocks to the data carriers  2 , but such further blocks are not elaborated herein. 
     A selection data block SDB contains a selection instruction code, a hash value HV and information concerning a given number of time slots TS as well as, indirectly, information concerning the length of such time slots TS. 
     A read data block RDB contains a read instruction code and information that from a memory of a data carrier  2  overall x data blocks DB (xDB) are to be read from x storage cells SB as from a storage cell bearing the address y, as well as, indirectly, information concerning the length of time slots TS. 
     A write data block WDB contains a write instruction code, a hash value HV as well as a data block DB which is to be written into a storage cell having the address m in a memory of a data carrier  2  as well as, indirectly, information concerning the length of time slots TS. 
     A stop data block HDB contains a stop instruction code and a hash value HV as well as, indirectly, information concerning the length of time slots. 
     A data carrier  2 , or several data carriers  2 , can be selected from a plurality of data carriers  2  by means of a selection data block SDB. 
     A predetermined number x of data blocks DB (xDB) can be read from a memory of a data carrier  2 , or from a respective memory of each of a plurality of data carriers  2 , by means of a read data block RDB. 
     Using a write data block WDB, a data block DB can be written into a storage cell SB of a data carrier  2  or into a respective storage cell SB of each of a plurality of data carriers  2 . 
     Using a stop data block HDB, a data carrier  2 , or a plurality of data carriers  2 , can be driven or set to a stop state in which a data carrier  2  does not respond to any further instruction data blocks arriving therein for as long as a data carrier  2  has not been withdrawn from the range of communication with the station  1 . It is only when a data carrier  2  is brought into the communication range of the station  1  again, in which case a so-called “power-on-reset” takes place in known manner, that a data carrier  2  can start to communicate with the station  1  again. 
     In the course of the communication between the station  1  and a data carrier  2 , the station  1  can also generate an acknowledge data block QDB. Using an acknowledge data block QDB, the station  1  informs a data carrier  2  first of all that the station  1  has correctly received an identification data block IDB transmitted to the station  1  by a data carrier  2 , and secondly that the instruction corresponding to an instruction data block previously transmitted to a data carrier  2  is to be executed by a data carrier  2 . The acknowledge data block QDB may be formed, for example as a data block containing a given bit pattern. 
     In the course of a communication between the station  1  and a data carrier  2 , a data carrier  2  transmits an identification data block IDB to the station  1 . The identification data block IDB is significant of the relevant data carrier  2 . Each data carrier  2  contains an identification data block IDB which is reserved specifically for this carrier and is issued only once. For example, such an identification data block IDB may represent a so-called serial number. 
     The construction of the station  1  will be described in detail hereinafter with reference to  FIG. 1 . 
     The station  1  includes sequencing means  3  which control a plurality of routines and functions, only the essential routines and functions thereof being described in detail hereinafter. 
     The station  1  also includes a clock signal generator  4  which generates a clock signal CLK having a frequency of 13.56 MHz. The clock signal CLK can be applied to the sequencing means  3  via a connection  28 . 
     The station also includes first generating means  5  which are arranged to generate the instruction data blocks, i.e. to generate selection data blocks SDB, read data blocks RDB, write data blocks WDB and stop data blocks HDB. The first generating means  5  can be controlled by the sequencing means  3  via a connection  6 . 
     The station  1  also includes second generating means  7  which are arranged to generate the acknowledge data block QDB. The second generating means  7  can be controlled by the sequencing means  3  via a connection  8 . 
     The station  1  also includes a time slot counter  9  which constitutes time slot determination means and whereby each time slot TS in time slot sequences TSS can be determined, each time slot sequence TSS consisting of a given number N of successive time slots TS. For example, a time slot sequence may consist of 1, 4, 8, 16, 32, 64, 128 or 256 time slots. The time slot counter  9  can be controlled by the sequencing means  3  via a connection  10 . The clock signal CLK can be applied to the time slot counter  9  via a connection  11 . The content of the time slot counter  9  can be applied to the second generating means  7  via a connection  12 . 
     The station  1  includes encoding means  13  which can receive the instruction data blocks SDB, RDB, WDB and HDB, generated by the first generating means  5 , as well as the acknowledge data block QDB, generated by the second generating means  7 , and can provide the encoding of the data blocks applied thereto. The encoding means  13  can be controlled by the sequencing means  3  via a connection  14 . 
     Modulation means  15  which can receive the encoded data blocks are connected to the encoding means  13 . In the present case the modulation means  15  are formed by amplitude modulation means which can receive a carrier signal CS and provide amplitude modulation of the carrier signal CS in dependence on the encoded data blocks supplied by the encoding means  13 . The amplitude modulation means  15  are arranged to carry out a 10% amplitude modulation (ASK 10%) and output an amplitude modulated carrier signal CSM. 
     The station  1  includes a carrier signal generator  16  for generating the carrier signal CS, which generator can receive the clock signal CLK via a connection  17  and generates the carrier signal CS in dependence on the clock signal CLK, which carrier signal also has a frequency of 13.56 MHz in this case. 
     Connected to the modulation means  15  are transmission/receiving means  18  which include a transmission coil  19  which can inductively transmit the amplitude modulated carrier signal CSM, output by the modulation means  15 , to receiving means of data carriers  2 . The transmission/receiving means  18  thus constitute transmission means. 
     The transmission/receiving means  18  at the same time constitute receiving means whereby signals inductively transmitted to the station  1  by data carriers  2  can be received. Such signals can be applied to demodulation means  21  of the station  1  via a connection  20 . The demodulation means  21  in the present case are arranged to demodulate a load modulated carrier signal CSB, because the inductive data transmission from the carriers  2  to the station  1  takes place in known manner by so-called load modulation of the carrier signal CS. Connected to the demodulation means  21  are decoding means  22  for the decoding of received data blocks. The decoding means  22  can be controlled by the sequencing means  3  via a connection  23 . Decoded identification data blocks EDB or data blocks xDB output by the decoding means  22  can be applied, via a connection  24 , to the sequencing means  3  in order to be subjected to further processing by means of the sequencing means  3 . 
     Collision detection means  25  which can be controlled by the sequencing means  3 , via a connection  26 , are connected to the decoding means  22 . The collision detection means  25  are arranged to detect collisions between two identification data blocks IDB, a collision of this kind being detected on a bit basis. Such a collision of identification data blocks BDB may occur when two or more identification data blocks EDB are received in the same time slot in the station  1 . When the collision detection means  25  detect such a collision of identification data blocks IDB, collision information CI is applied to the sequencing means  3 , via a connection  27 , so that the sequencing means  3  can perform an appropriate control operation which will be described in detail hereinafter. 
     The construction of the data carrier  2  will be described in detail hereinafter on the basis of the data carrier  2  shown in  FIG. 2 . 
     The data carrier  2 , being constructed for contactless communication with a station which is constructed at least for reading, such as the station  1  of  FIG. 1 , includes receiving/transmission means  30  which include a transmission coil  31  and constitute receiving means for receiving data blocks DB as well as transmission means for transmitting data blocks DB. 
     The data carrier  2  includes a circuit  32  whose parts which are of essential importance in the present context are shown in  FIG. 2 . The circuit  32  is constructed as an integrated circuit. The circuit  32  includes a first terminal  33  and a second terminal  34  which are connected to the receiving/transmission means  30 . In this case the first terminal  33  forms a receiving terminal for receiving data blocks DB, received by means of the receiving/transmission means  30 , as well as a transmission terminal for outputting data blocks DB to be transmitted by means of the transmission/receiving means  30 . The circuit  32  includes sequencing means  34  whereby a plurality of routines and functions of the data carrier  2  can be controlled; however, only the routines and functions thereof which are of relevance in the present context will be described in detail hereinafter. 
     The circuit  32  also includes storage means  36  which are formed by an EEPROM in the present case. However, the storage means  36  may also be implemented in a different manner. The storage means  36  include a first storage section  37  and a second storage section  38 . The storage section  37  is arranged to store the identification data block IDB characterizing the data carrier  2 . The identification data block IDB consists, for example of a total of 8 bytes comprising 8 bits each. The first storage section  37  can also be controlled, via a connection  39 , by the sequencing means  35  in order to output the identification data block IDB stored in the first storage section  37  via a connection  40 . Moreover, the first storage section  37  can be controlled by the sequencing means  35  via a further connection  41 . Via the connection  41 , the first storage section  37  can receive a bit address BA(HV) which corresponds to a hash value HV and forms an initial address for a part PM of the identification data block IDB stored in the first storage section  37 . The part PM, determined by the hash value HV, of the identification data block IDB can be output via a connection  42  by controlling the first storage section  37  via the connection  41 . 
     The second storage section  38  of the storage means  36  consists of a total of N storage cells SB 1  . . . SBm . . . SBN, each storage cell SB being arranged to sore a total of 4 bytes. The second storage section  38  can be controlled by the sequencing means  35 , via a connection  43 , either to read a predetermined number x of data blocks DB from the second storage section  38  for output via a connection  44 , or to store a data block DB, applied to the second storage section  38  via a connection  45 , in one of the storage cells SB 1  . . . SBm . . . SBN. 
     The data carrier  2  includes demodulation means  46  which constitute amplitude demodulation means which are connected to the first terminal  33  and are suitable for demodulating the amplitude modulated carrier signal CSM transmitted by a station  1 . The demodulation means  46  output the data blocks DB, transmitted to the data carrier  2 , in demodulated but still encoded form via an output  47 . 
     The data carrier  2  also includes clock signal regenerating means  48  which are also connected to the first terminal  33 . The clock signal regenerating means  48  can regenerate the clock signal CLK from the received amplitude modulated carrier signal CSM so that he clock signal CLK is available in the data carrier  2  as well as in the station  1  transmitting the modulated carrier signal CSM. The regenerated clock signal CLK is applied to the sequencing means  35  via a connection  49 . 
     The data carrier  2  also includes DC voltage generating means  50  which are also connected to the first terminal  33  and can generate, while using the amplitude modulated carrier signal CSM, a DC supply voltage V which serves to power the entire circuit  32 . It is to be noted that the DC voltage generating means  50  include voltage limiting means in order to prevent in known manner the occurrence of an excessive supply voltage V. 
     Reset signal generating means  52  are connected to the DC voltage generating means  50 , via a connection  51 , in order to generate a reset signal RS upon occurrence of a DC supply voltage V; this is the case when the data carrier  2  enters the communication range of a station  1 , said reset signal being capable of initiating a so-called “power-on-reset”. The reset signal RS can be applied to the sequencing means  35  via a connection  53 . 
     The data carrier  2  includes a series of decoding means for the decoding of encoded data blocks which appear on the output  47  of the demodulation means  46 ;  FIG. 2  shows a total of six of such decoding means. These means are first decoding means  54  for decoding a selection data block SDB, second decoding means  55  for decoding an acknowledge data block QDB, third decoding means  56  for decoding a read data block RDB, fourth decoding means  57  for decoding a write data block WDB, fifth decoding means  58  for decoding a stop data block HDB, and sixth decoding means  59  for decoding data blocks DB to be stored in the second storage section  38 . The inputs of the above-mentioned decoding means  54 ,  55 ,  56 ,  57 ,  58  and  59  are connected to the output  47  of the demodulation means  46 . The first decoding means  54  can be controlled by the sequencing means  35  via a connection  60 ; the second decoding means  55  can be controlled thereby via a connection  61 , the third decoding means  56  via a connection  62 , the fourth decoding means  57  via a connection  62 , the fifth decoding means  58  via a connection  64 , and the sixth decoding means  59  via a connection  65 . The outputs of the decoding means  54 ,  55 ,  56 ,  57  and  58  are connected to the sequencing means  35  via connections  66 ,  67 ,  68 ,  69  and  70  so that the decoded data blocks SDB, QDB, RDB, WDB and HDB can be applied to the sequencing means  35  for the purpose of further processing. The connection  45  which leads to the second storage section  38  is connected to the output of the sixth decoding means  59 . 
     To the output of the first decoding means  54  there are connected determination means  71  which can be controlled by the sequencing means  35  via a connection  72 . The determination means  71  are arranged and constructed so as to determine a hash value HV which is contained in a selection data block SDB to be transmitted to the data carrier  2 . A hash value HV determined by means of the determination means  71  can be output to the sequencing means  35 , via a connection  73 , in order to be further processed in the sequencing means  35 . 
     To the output of the second decoding means  55  there are connected test means  74  which can be controlled by the sequencing means  35  via a connection  75 . The test means  74  are constructed in such a manner that they can test the validity of an acknowledge data block QDB. In case an acknowledge data block QDB is characterized by a given bit pattern, as mentioned before, the test means  74  test whether an acknowledge data block QDB received contains exactly the relevant bit pattern. In the case of a positive test result, i.e. when a valid acknowledge data block QDB has been received, the test means  74  generate an “acknowledge valid” signal QV which can be applied, via a connection  76 , to the sequencing means  35  for further processing. 
     The circuit  32  of the data carrier  2  also includes encoding means  77 , the input of which is connected to a connection  78  which is connected to the connection  40  as well as to the connection  44 . The encoding means  77  can be controlled by the sequencing means  35  via a connection  79 . The encoding means  77  are capable of encoding the identification data block IDB read from the first storage section  37  as well as the data blocks xDB read from the second storage section  38 . After completion of the encoding by means of the encoding means  77 , the encoded data blocks can be applied to modulation means  80 . In the modulation means  80  an auxiliary carrier signal is subjected in known manner to a modulation corresponding to the encoded data blocks, after which the modulated auxiliary carrier signal is applied, via the first terminal, to the receiver/transmitter means  30  so as to be inductively transmitted to a station  1 . 
     The circuit  32  of the data carrier  2  also includes a so-called CRC 8 -stage  81  which can be controlled by the sequencing means  35  via a connection  82 . The CRC 8 -stage  81  can receive, via the connection  42 , the part PM of the identification data block DB which was read from the first storage section  37  in conformity with the hash value HV, determined by the determination means  71 , by means of the sequencing means  35 . The part PM applied to the CRC 8 -stage  81  is shifted through the CRC 8 -stage  81 ; during this operation an algorithm that can be implemented by the CRC 8 -stage  81  is executed, after which a given value n is obtained at the output of the CRC 8 -stage  81 . The value n is subsequently stored in a time slot register  83  which can be controlled by the sequencing means  35  via a connection  84 . 
     The circuit  32  of the data carrier  2  also includes a time slot counter  85  which can be controlled by the sequencing means  35  via a connection  86 . The time slot counter  85  constitutes time slot determination means. The time slot counter  85  is arranged to determine each time slot TS of possibly repeatedly successively running time slot sequences TSS. Each of these time slot sequences TSS consists of a given number N of successive time slots TS. The number N that can be determined by means of the time slot counter  85  and the length of the successive time slots TS of time slot sequences TSS always correspond to the number and the length of the time slots TS of time slot sequences TSS determined by the time slot counter  9  of a station  1 . The time slot counter  85  can receive, via the connection  49  and a further connection  87 , the clock signal CLK regenerated by means of the clock signal regenerating means  48 . On the basis of the regenerated clock signal CLK, the time slot counter  85  determines each time slot TS of successively running time slot sequences TSS. The relevant content of the time slot counter  85  can be applied from the output of the time slot counter  85 , via a connection  88 , to the sequencing means  35  so that the relevant contents are available for control purposes in the sequencing means  35 . 
     The circuit  32  of the data carrier  2  also includes a comparator  89  which can be controlled by the sequencing means  35  via a connection  90 . The comparator  89  can receive, via a connection  91 , the content n of the time slot register  83  as well as, via the connection  92 , the content of the time slot counter  85 . The comparator  89  provides a comparison of the contents received and outputs, in the case of corresponding received contents, a comparator signal COS to the sequencing means  35  via a connection  93 . Communication between the data carrier  2  and a station  1  can be enabled for a given time slot TS in dependence on the comparator signal COS as will be described in detail hereinafter. 
     The first decoding means  54  constitute first processing means which are arranged to process, i.e. to decode, a selection data block SDB which is transmitted by a station  1  in order to initiate a selection operation and is received via the terminal  33 , said selection data block enabling the selection of the data carrier  2  from a plurality of data carriers  2 . 
     The encoding means  77  constitute second processing means which are arranged to process, after the processing, i.e. the encoding, of a received selection data block SDB by means of the first processing means, so the first encoding means  54 , an identification data block IDB which is stored in the circuit  32  of the data carrier  2  and can be applied, during the duration of a given time slot TS of a time slot sequence TSS, after its processing by means of the second processing means, so the encoding means  77 , to the receiving/transmission means  30 , via the terminal  33 , for transmission to the station  1 . The given time slot should be the n th  time slot, where 1≦n≦N. 
     The second decoding means  55  constitute third processing means which are arranged to process, i.e. to decode, after correct reception of an identification data block IDB transmitted by the data carrier  2  to a station  1 , an acknowledge data block QDB which is transmitted by the station  1  to the data carrier  2  and is received via the terminal  33 , which acknowledge data block can set the circuit  32  of the data carrier  2  to a “selected” state as will be described in detail hereinafter. 
     The time slot register  83  in the data carrier  2  constitutes time slot fixation means which can fix, after the processing of the acknowledge data block QDB by means of the third processing means, so the second decoding means  55 , the respective n th  time slot TS of successively generated time slot sequences TSS for the circuit  32  of the data carrier  2 , or the data carriers  2 , as will be described in detail hereinafter. 
     The comparator  89  and the sequencing means  35  constitute control means  94  by means of which control means  94 , after fixation of the circuit  32  of the data carrier  2  to the respective n th  time slot TS, communication can be enabled between the data carrier  2  and a station  1  only during the respective n th  time slot TS fixed for the circuit  32  of the data carrier as will also be described in detail hereinafter. 
     The part of the operation of the station  1  of  FIG. 1  which is essential in this context will be described in detail hereinafter with reference to the time diagram shown in  FIG. 5  and with reference to a program run which will be described in conformity with the flow chart given in  FIG. 3 . 
     This program run starts in a block  100 . During a next block  101 , a selection data block SDB is generated, using the first generating means  5 , in order to initiate a selection operation as indicated on line  1  of  FIG. 5 . In a next block  102 , the previously generated selection data block SDB is encoded by means of the encoding means  13 ; this means at the same time that the encoded selection data block SDB is amplitude modulated by means of the modulation means  15  and subsequently transmitted, using the transmission/receiving means  18 , to all data carriers  2  present in the communication range of the station  1 . 
     During a next block  103 , the content of the time slot counter  9  is set to the value “0”; the first time slot TS 0  of a first time slot sequence TSS 1  then runs as appears from line  1  of  FIG. 5 . 
     After the transmission of the selection data block SDB, it may occur that during the first time slot TS 0  of the first time slot sequence TSS 1  either no data carrier  2  responds or exactly one data carrier  2  responds or more than one data carrier  2  respond and transmit their identification data block DB to the station  1 . 
     During a block  104  each identification data block IDB received is decoded by means of the decoding means  22 , after which the identification data block IDB is applied to the sequencing means  3 . During a block  105 , it is subsequently detected, using the collision detection means  25 , whether a collision has occurred between at least two identification data blocks IDB or whether no identification data block IDB has even been received and decoded. When it is determined in the block  105  that only a single identification data block IDB has been decoded, during a subsequent block  106  the generating of the acknowledge data block QDB by means of the second generating means  7  is initiated. Subsequently, in a block  107  the acknowledge data block QDB generated is encoded by means of the encoding means  13 , with the result that the carrier signal CS is modulated in conformity with the encoded acknowledge data block by means of the modulation means  15 ; subsequently, the modulated carrier signal CSM is transmitted to the data carrier  2  wherefrom the identification data block IDB has been received in the first time slot TSO in conformity with the block  104 . 
     The program run then continues in a block  108 . In the block  108  the program run is continued also if a collision between at least two identification data blocks IDB or non-reception of an identification data block DB is detected in the block  105 . In the block  108  the content of the time slot counter  9  is incremented by the value “1”. This means that the second time slot TS 1  of the first time slot sequence TSS 1  runs. 
     Subsequently, in a block  109  it is checked whether the last time slot TSN has already been passed, so whether the last time slot TSN has already elapsed. If this is not the case, the program run is continued in the block  104 , after which the blocks  105 ,  106 ,  107 ,  108  and  109  are completed again; as assumed in conformity with  FIG. 5 , for example each time only one data carrier  2  has then transmitted an identification data block EDB to the station  1  during the second time slot TS 1 , during the fourth time slot TS 3 , during the sixth time slot TS 5 , and during the last but one time slot TS 254  of the first time slot sequence TSS 1 , whereas in all other time slots TS of the first time slot sequence TSS 1  either a collision between two identification data blocks IDB has been detected or non-reception of identification data blocks IDB. 
     When the last time slot TSN, being the time slot TS 255  in the example shown in  FIG. 5 , of the first time slot sequence TSS 1  has elapsed, and hence this sequence is subsequently exceeded, the program run is continued in a block  110  in conformity with the flow chart of  FIG. 3 . 
     In the block  110  it is checked whether a read data block RDB is to be transmitted. Information in this respect is contained in the sequencing means  3 . When a read data block RDB is to be transmitted, subsequently in a block  111  such a read data block RDB is generated by means of the first generating means  5  for the purpose of initializing a read operation; this is shown on line  3  in  FIG. 5 . Subsequently, in a block  112  the read data block RDB generated is encoded by means of the encoding means  13 , with the result that, after modulation by means of the modulation means  15 , the generated and encoded read data block RDB is transmitted to all data carriers  2  selected in the course of the preceding selection operation during the first time slot sequence TSS 1 . 
     Subsequently, in a block  113  the content of the time slot counter  9  is set to the value “0”; the first time slot TSO of a second time slot sequence TSS 2  then runs as can be deduced from line  3  of  FIG. 5 . As is shown in  FIG. 5 , the length of the time slots TS of the second time slot sequence TSS 2  is shorter than the length of the time slots TS of the first time slot sequence TSS 1 . This is automatically imposed by the sequencing means  3 , because the sequencing means  3  contain information concerning the previously executed generating of a read data block RDB and hence know that only shorter time slots TS are required, because less time is required for read operations. 
     After the block  113 , the program run continues in a block  114  in which the predetermined number x of data blocks DB, transmitted to the station  1  by the data carrier  2  selected in the first time slot TS 0 , are decoded by means of the decoding means  22 . The decoded data blocks xDB are applied, via the connection  24 , to the sequencing means  3  and are further processed by the sequencing means  3 ; however, this processing will not be elaborated upon herein. 
     Subsequently, in a block  115  the content of the time slot counter  9  is incremented by the value “1”; the second time slot TS 1  of the second time slot sequence TSS 2  then runs. Subsequently, in a block  116  it is checked whether the last time slot TS 255  has already been passed. If this is not the case, the program run is continued in the block  114 , after which the blocks  115  and  116  are completed again; in the time slots TS 1 , TS 3 , TS 5  and TS 254  each time x data blocks DB (xDB) are then successively transmitted to the station  1  by a respective data carrier in the time slots TS 1 , TS 3 , TS 5  and TS 254  of the second time slot sequence TSS 2 ; these blocks are decoded by means of the decoding means  22  and applied, via the connection  24 , to the sequencing means  3  for further processing. 
     When the test in the block  116  yields a positive result, the program run is continued in a block  117  in which it is continued even when a negative test result is obtained in the block  110 , i.e. if no read operation is desired. In the block  117  it is tested whether a write data block WDB is to be transmitted, i.e. whether the station  1  should perform a write operation in the data carriers  2  selected in the previously counted time slots TS 1 , TS 3 , TS 5  and TS 254 . Information in this respect is contained in the sequencing means  3 . 
     If the test result in the block  117  is positive, in order to initiate a write operation the generating of a write data block WDB by means of the first generating means  5  is then initiated in a block  118  as indicated on line  4  of  FIG. 5 . In a block  119  the write data block WDB generated is subsequently encoded by means of the encoding means  13 , with the result that, after an appropriate modulation by means of the modulation means  15 , the encoded write data block is applied to all data carriers  2  previously selected in the course of the selection operation during the first time slot sequence TSS 1  (see lines  1  and  2  of  FIG. 5 ). 
     After the transmission of the write data block WDB to all selected data carriers  2 , each time fixed to a respective time slot TS, the program run is continued in a block  120 . In the block  120  the content of the time slot counter  9  is set to the value “0” again; the first time slot TSO of a third time slot sequence TSS 3  then runs as indicated on line  4  of  FIG. 5 . The length of the time slots TS of the third time slot sequence TSS 3  is again fixed, using the sequencing means  3 , to the value which has already been fixed for the time slots TS of the first time slot sequence TSS 1 , as appears from  FIG. 5 . 
     Subsequently, the program run is continued in a block  121 . In the block  121  the identification data block DDB to be transmitted in the course of a write operation by the data carrier  2  fixed to the first time slot TS 0  is awaited and, after its arrival, it is decoded by means of the decoding means  22 , after which the identification data block IDB is applied to the sequencing means  3 . Subsequently, for reasons of safety it is checked again in a block  122  whether a write operation is to be performed indeed for the data carrier  2  fixed to the first time slot TS 0 . If this test offers a positive result, the program run is continued in a block  123  in which the second generating means  7  generate an acknowledge data block QDB. Subsequently, in a block  124  the generated acknowledge data block QDB is encoded by means of the encoding means  13 ; using the modulation means  15  and the transmission/receiving means  18 , the acknowledge data block QDB is then transmitted to the data carrier  2  fixed to the first time slot TS 0 . As soon as the acknowledge data block QDB arrives in the data carrier  2  fixed to the first time slot TS 0  and is recognized as being valid in the relevant data carrier  2 , the write operation is indeed executed for the relevant data carrier  2 . 
     The program run subsequently continues in a block  125  in which the content of the time slot counter  9  is incremented by the value “1”; the second time slot TS 1  of the third time slot sequence TSS 3  then runs. Subsequently, in a block  126  it is checked whether the last time slot TS 255  of the third time slot sequence TSS 3  has been passed. For as long as this is not the case, the program run is continued in the block  121 , after which the blocks  122 ,  124 ,  125 , and  126  are completed again. As a result, in the course of the write routine activated by the write data block WDB a respective write operation is also performed in the data carrier  2  fixed to the second time slot TS 1 , and in the data carrier  2  fixed to the fourth time slot TS 3  and (not shown in  FIG. 5 ) in the two data carriers  2  fixed to the time slots TS 5  and TS 254  of the third time slot sequence TSS 3 . 
     When the last time slot TS 255  of the third time slot sequence TSS 3  has been passed, the program is continued in a block  127  in which it continues also in the case of a negative test result in the block  117 . The block  127  is representative of an operation which can be executed by the station  1  in all selected data carriers  2 .(not described herein) and is terminated in a block  128 . 
     Subsequently, the program continues in a block  129  in which it is checked whether the station  1  should transmit a stop data block HDB to each selected data carrier  2  fixed to a respective time slot TS. The information in this respect is contained in the sequencing means  3 . In the case of a positive test result in the block  129 , the program run continues in a block  130  in which, in order to initiate a termination operation or stop operation, a stop data block HDB is generated by means of the first generating means  5  as indicated on line  6  of  FIG. 5 . Subsequently, in a block  131  the stop data block HDB generated is encoded by means of the encoding means  13 , so that it is transmitted to all selected data carriers  2 . Subsequently, in a block  132  the content of the time slot counter  9  is set to the value “0”, so that the first time slot TS 0  of a fourth time slot sequence TSS 4  is activated as appears from line  6  of  FIG. 5 . The length of the time slots TS of the fourth time slot sequence TSS 4  corresponds to the length of the time slots TS of the first time slot sequence TSS 1  and of the third time slot sequence TSS 3 . The length is fixed by the sequencing means  3 . 
     Subsequently, in a block  133  the identification data block IDB transmitted by the data carrier  2  fixed to the first time slot TS 0  is decoded, after which the identification data block IDB is applied to the sequencing means  3 . 
     Subsequently, in a block  134  it is checked whether a termination operation or stop operation is to be executed indeed. This test is performed by means of the sequencing means  3 . In the case of a positive test result, the second generating means  7  generate an acknowledge data block QDB in a block  135 , which acknowledge data block is encoded by means of the encoding means  13  in a block  136  and subsequently transmitted to the data carrier  2  fixed to the first time slot TS 0 . The acknowledge data block QDB received in the data carrier  2  in this case ensures that the data carrier  2  is set to a “stop” state in which this data carrier does not respond to any further instructions or instruction data blocks for as long as it remains within the communication range of the station  1 . 
     Subsequently, the program run continues in a block  137  in which the content of the time slot counter  9  is incremented by the value “1”; the second time slot TS 1  of the fourth time slot sequence TSS 4  then runs. Subsequently, in a block  138  it is tested whether the last time slot TS 255  of the fourth time slot sequence TSS 4  has already been passed. For as long as this is not the case, the program run cyclically continues through the blocks  133 ,  134 ,  135 ,  136 ,  137  and  138 . The data carriers  2  fixed to the time slots TS 1  and TS 3  are then set to their respective “stop” states, as appears from  FIG. 5 , and the data carriers  2  fixed to the time slots TS 5  and TS 254  are also set to their “stop” state; however, the latter is not shown in  FIG. 5 . 
     Subsequent to the block  138 , the program run is continued in the block  101 ; it also continues therein in the case of a negative test result in the block  129 . During the renewed execution of the block  101 , a selection data block DSB is again generated as shown on line  8  of  FIG. 5 , after which a fifth time slot sequence TSS 5  is generated in which a respective single data carrier  2  is selected again in given time slots TS, said data carrier being fixed to the relevant time slot after successful selection as shown on line  8  of  FIG. 5  for the second time slot TS 1  of the fifth time slot sequence TSS 5 . 
     The operation of the data carrier  2  according to the invention will be described in detail hereinafter with reference to  FIG. 2  and on the basis of the time diagram of  FIG. 5  and with reference to a program run which will be described in detail hereinafter with reference to the flow chart shown in  FIGS. 4A and 4B . 
     The program run commences in a block  140  and continues in a block  141  in which a so-called “power-on-reset” operation takes place; this is the case if the reset signal generating means  52  apply a reset signal RS to the sequencing means  35 . This occurs whenever the data carrier  2  enters the communication range of the station  1  of  FIG. 1 . 
     Subsequently, in a block  142  the data carrier  2 , or the circuit  32  of the data carrier  2 , is set to a “non-selected” state. 
     Subsequently, in a block  143  the first decoding means  54  are activated. Subsequently, in a block  144  it is tested whether a selection data block SDB has been decoded by means of the first decoding means  54 . For as long as this is not the case, the program run is continued again in the block  143  and subsequently in the block  144 , so that these two blocks  143  and  144  are successively completed for as long as no selection data block SDB is received and decoded. 
     As soon as a selection data block SDB is received by the data carrier  2  and decoded by means of the first decoding means  54 , the program run continues in a block  145  in which the hash value HV, contained in the previously decoded selection data block SDB, is determined by means of the determination means  71 ; this hash value HV is subsequently applied, via the connection  73 , to the sequencing means  35  so that the first storage section  37  can be controlled, via the sequencing means  35 , so as to fix the part PM of the identification data block IDB. 
     Subsequently, in a block  146  the part PM of the identification data block IDB, stored in the first storage section  37 , is determined in conformity with the hash value HV previously determined from the decoded selection data block SDB by means of the determination means  71 . Subsequently, in a block  147  the previously determined part PM, applied to the CRC 8 -stage  81  via the connection  42 , is shifted through the CRC 8 -stage  81 , resulting in a value n on the output of the CRC 8 -stage  81  which represents a CRC 8  result. The CRC 8  result, being the value n, is subsequently stored in the time slot register  83  in a block  148 . A time slot TS bearing the number n for the data carrier  2  has thus been selected by means of the CRC 8  result, so by means of the value n. 
     Subsequently, the program run is continued in a block  149  in which the content of the time slot counter  85  of the data carrier  2  is set to the value “0”, the first time slot TS 0  of the first time slot sequence TSS 1  then runs, that is to say in perfect synchronism with the events in the station  1 . 
     Subsequently, in a block  150  it is tested whether the content of the time slot counter  85  corresponds to the content of the time slot register  83 . If this is not the case, the program run continues in a block  151  in which the content of the time slot counter  85  is incremented by the value “1”. Subsequently, the program run is continued in the block  150 . The blocks  150  and  151  are cyclically successively completed for as long as the content of the time slot counter  85  and the time slot register  83  differ. 
     However, as soon as the test in the block  150  reveals that the content of the time slot counter  85  corresponds to the content of the time slot register  83 , the program run is continued in a block  152 . In the block  152  the identification data block IDB stored in the first storage section  37  is read and applied to the encoding means  77 , via the connections  40  and  78 , after which the identification data block IDB is encoded accordingly in a block  153  by means of the encoding means  77 , with the result that subsequently modulation by means of the modulation means  80  and transmission of the identification data block DB to the station  1  take place. 
     Subsequently, in a block  154  the second decoding means  55  are activated, so that the second decoding means  55  are ready to decode the acknowledge data block QDB awaited from the station  1 . Upon arrival of such an acknowledge data block QDB transmitted by the station  1 , in a block  155  the received acknowledge data block QDB is decoded by means of the second decoding means  55 . Subsequently, in a block  156  the test means  74  test whether the received acknowledge data block QDB is valid. If this is not the case, the program run is continued in block  143 . 
     However, if the testing by means of the test means  74  in the block  156  produces a positive result, i.e. when the test means  74  output an “acknowledge valid” signal QV, via the connection  76 , to the sequencing means  35 , the program run is continued in a block  157  in which, using the sequencing means  35 , the content of the time slot register  83 , i.e. the value n, is fixed via the connection  84 . This means that the time slot TS, previously selected for the data carrier  2 , bearing the number n is now fixed for the data carrier  2  or for the circuit  32  of the data carrier  2 , so that each time the no time slot TS of successively generated time slot sequences TSS is fixed for the data carrier  2  or for the circuit  32  of the data carrier  2 . 
     Depending on whether the content of the time slot register  82  was fixed in the block  157 , the program run is continued in a block  158  in which the data carrier  2 , or the circuit  32  of the data carrier  2 , is set to the state “selected”. This means that the data carrier  2  has the status of a data carrier which has been unambiguously identified and hence selected by the station  1  for as long as the data carrier  2  is within the communication range of the station  1 . 
     Subsequently, in a block  159  the third decoding means  56  are activated so that they are ready to decode a read data block RDB. Subsequently, in a block  160  the fourth decoding means  57  are activated so that they are ready to decode a write data block WDB. It may occur that subsequently in a block  161  further decoding means are activated so as to be ready for the decoding of data blocks. In conformity with the block  161 , for example the activation of the sixth decoding means  59  may also take place. Subsequently, in a block  162  the fifth decoding means  58  are activated so that they are ready to decode a stop data block HDB. 
     Subsequently, the program run involves a block  163 , a block  164 , a block  165  and a block  166 . In the block  163  it is tested whether a read data block RDB has been decoded. In the block  164  it is tested whether a write data block WDB has been decoded. In the block  165  it is tested whether a further data block, which has not been elaborated upon, has been decoded. In the block  166  it is tested whether a stop data block HDB has been decoded. For as long as a negative test result is obtained in all four blocks  163 ,  164 ,  165  and  166 , the blocks  163 ,  164 ,  165  and  166  are cyclically completed in succession. 
     However, if a positive test result is detected in the block  163 , the program run is continued in a block  167 . In the block  167  the content of the time slot counter  85  is set to the value “0”. Subsequently, in a block  168  it is tested whether the content of the time slot counter  85  corresponds to the fixed content of the time slot register  83 . If this is not the case, subsequently in a block  169  the content of the time slot counter  85  is incremented by the value “1”, after which the program run is continued in the block  168 . The blocks  168  and  169  are cyclically completed in succession for as long as the content of the time slot counter  85  deviates from the fixed content of the time slot register  83 . 
     As soon as the content of the time slot counter  85  corresponds to the fixed content of the time slot register  83 , the program run is continued in a block  170 . In the block  170  the sequencing means  35  control the second storage section  38  of the storage means  36  in such a manner that overall x data blocks DB (xDB) are read from x storage cells SB (xSB) as from a storage cell SB bearing the address y (SBy), said blocks being applied to the encoding means  77  via the connection  44  and the connection  78 . In a subsequent block  171 , the previously read x data blocks DB (xDB) are encoded, with the result that the x data blocks DB (xDB) are transmitted to the station  1  after appropriate modulation by means of the modulation means  80 . 
     For example, if the value n=0 is fixed in the time slot register  83  in the data carrier  2  shown in  FIG. 2 , the data carrier  2  will be read during the first time slot TS 0  of the second time slot sequence TSS 2 , so that x data blocks DB are then transmitted to the station  1  in the first time slot TS 0 . Line  3  of  FIG. 5  diagrammatically represents a read operation in which, after the station  1  has output a read data block RDB to all selected data carriers  2  present in the communication range, each time a respective data carrier  2  from among the addressed data carriers  2  is read in the time slot TS 0  or TS 1  or TS 3  or TS 4  or TS 254 . As is shown, a major advantage resides in the fact that the station  1  need output only a single read data block RDB for all selected data carriers  2  in order to initiate a read operation in these data carriers  2 ; each selected data carrier is advantageously fixed to a time slot TS and realizes a data communication with the station  1  only in the respective time slot reserved for the relevant data carrier, said data communication consisting of a read operation in the described case. 
     Subsequent to the block  171 , the program run is continued in the block  163 . When the test result in the block  163  is negative, the program run is continued in the block  164 . 
     If the test in the block  164  reveals that a write data block WDB has been decoded by means of the fourth decoding means  57 , the program run is continued in a block  172 . In the block  172  the content of the time slot counter  85  is set to the value “0” again. Subsequently, in a block  173  it is tested whether the content of the time slot counter  85  corresponds to the fixed content of the time slot register  83 . If this is not the case, in a block  174  the content of the time slot counter  85  is incremented by the value “1”, after which the program run is continued in the block  173 . 
     When the content of the time slot counter  85  corresponds to the fixed content of the time slot register  83 , the program run is continued in a block  175 . In the block  175  the identification data block DB stored in the first storage section  37  is read and applied to the encoding means  77 . Subsequently, in a block  176  the identification data block IDB is encoded by means of the encoding means  77 ; this results in a modulation by means of the modulation means  80  and a transmission of the identification data block IDB to the station  1 . 
     Subsequently, in a block  177  the second decoding means  55 , awaiting the arrival of the acknowledge data block QDB to be transmitted by the station  1  and awaited by the data carrier  2 , are activated. After the arrival of the acknowledge data block QDB, a decoding operation is performed by means of the second decoding means  55  in a block  178 , so that the acknowledge data block QDB thus decoded is applied on the one hand to the sequencing means  35  and on the other hand to the test means  74 . Subsequently, in a block  179  it is tested whether the received acknowledge data block is valid. If this is not the case, the program run is continued in the block  163 . However, if the test result in the block  179  is positive, the program run is continued in a block  180 . In the block  180  a data block DB is written, using the sequencing means  35 , into a storage cell SB bearing the address m, said data block DB having been determined from the write data block WDB decoded in conformity with the block  164 . Subsequent to the block  180 , the program run is continued in the block  163 . 
     The write operation shown on the lines  4  and  5  in  FIG. 5  is executed by completion of the blocks  164  and  172  to  180 . This write operation is preferably initiated by a single write data block WDB output by the station  1 , after which every validly acknowledged selected data carrier  2  transmits its identification data block IDB to the station  1  in the time slot TS reserved for the relevant data carrier  2 , after which the station  1  returns an acknowledge data block QDB to the relevant data carrier  2 . The transmission of the identification data block IDB and that of the acknowledge data block QDB take place each time in the time slot TS reserved for a data carrier  2 . The actual write operation in each data carrier  2  takes place after the time slot TS reserved for the relevant data carrier  2  has elapsed; this is why the actual write operation is not shown on the lines  4  and  5  of  FIG. 5 . 
     When subsequently the test result in the blocks  163  and  164  is negative, the program run is continued in the block  165  which is representative of the testing of a further data block which is not further specified herein. After the block  165 , the program run is continued in a block  181  which is representative of the execution of a further communication operation. Subsequent to the block  181  the program run is continued again in the block  163 . 
     When subsequently the test results in the blocks  163 ,  164  and  165  are negative, the program run is continued in the block  166 . In the block  166  it is tested whether a stop data block HDB has been decoded by means of the fifth decoding means  58 . As soon as the station  1  outputs such a stop data block HDB and hence such a stop data block HDB is decoded by the fifth decoding means  58 , the program run is continued in a block  182 . Subsequent to the block  182 , the program run is continued in the blocks  183 ,  184 ,  185 ,  186 ,  187 ,  188 ,  189  and  190 . The steps corresponding to the blocks  182  to  189  are fully identical to the steps corresponding to the blocks  172  to  179 , so that they will not be described again. 
     Whereas subsequent to the block  179  a data block DB is written into a storage cell SB in the block  180 , in the block  190  the relevant data carrier  2  is set to a “stop” state. In this stop state the relevant data carrier  2 , selected during a previous selection operation (see lines  1  and  2  of  FIG. 5 ) and subsequently read during a read operation (see line  3  of  FIG. 5 ) and subsequently written during a write operation (see lines  4  and  5  of  FIG. 5 ) and then set to its “stop” state during a termination operation (see lines  6  and  7  of  FIG. 5 ), no longer responds to further instructions or instruction data blocks. 
     The transmission of a single stop data block HDB for all selected data carriers  2  by the station  1 , thus sets all validly acknowledged selected data carriers  2 , each of which is fixed to a time slot TS, to their “stop” state, so that they cannot perform a further communication with the station  1 . 
     Subsequently, the program run is continued in a block  191  in which the sequencing means  35  proceed to the block  141  after the start block  140  of the program run. As a result, an already selected data carrier  2  which was subsequently set to its stop state can participate in a data communication with the station  1  only after the data carrier  2  has first been removed from the communication range of the station  1  and subsequently brought into the communication range of the station  1  again. 
     The invention is not restricted to the described embodiment. In this context it is to be noted notably that it is also possible to select a different number of time slots TS for successively generated time slot sequences TSS. For example, the number of time slots TS per time slot sequence TSS can be controlled in dependence of previously determined collisions. Furthermore, the value which can be stored in a time slot register and is subsequently fixed may be chosen in a manner other than by means of a part PM of an identification data block IDB, for example by means of a random generator.