Data transfer method for a radio frequency identification system

The invention relates to a method for transferring data in a Radio frequency identification system from one transponder to one Reading device by load modulation of a device sent by the reader interrogation signal

In the identification of persons, animals and objects, In recent years, a system in which a (stationary or portable) (Reader) has an object associated with the object to be identified Transponders via an alternating field, whereupon the Transponder with the transmission of the data stored in it Answers. The frequency range is also used Radio frequency identification systems, or RFID.

An RFID transponder generally consists of an antenna coil and An integrated circuit, all the necessary electronic Circuit blocks, such as, for example, for voltage supply, clock generation, To control the process and to store the data required for identification Necessary data. The parallel to the antenna coil Capacity is also often part of the integrated circuit. they But can also be formed by a discrete structural element.

The RFID reader consists of a resonant circuit with a transmitting coil And a capacity derived from a driver stage with a signal having a Generally fixed frequency (eg, 125 kHz). Further The reader contains electronic circuit blocks to control the signals generated by the Absorbance modulation from the transponder And to transmit data and commands, for example by modulating the field, to the Transponders.

Reader and transponders form at the data or at the A loose coupled transformer. Therefore, the Energy transfer is relatively low.

For most identification applications of transponder reader It is desirable and advantageous if the identification Ie the data exchange between transponder and reader without Delay. For example, in the application in FIG Immobilizer the problem is that when starting a car the user A duration of more than 150 ms, from turning the ignition key to the Starting the engine, as a time delay. It follows that the Entire transmission protocol in this very short period of time have to be.

When the field is turned on, the reader needs approximately two Milliseconds before the high coil voltage of about 100 volts And the modulation generated by the transponder Low useful signal in the amount of a few millivolts and thus the Data can be decoded correctly. The first from the transponder Sent ID code is thus only detected at the second sequence, Which means a time delay of the data protocol. A similar Problem occurs when switching from an undamped to a damped one State, such as, for example, at the end of a write sequence or a programming sequence, on.

It is therefore an object of the invention to provide a method for transferring Data in a radio frequency identification system of one Transponders to a reading device by means of load modulation Which is transmitted by a One-time data transfer provides the correct result.

This object is achieved by a method with the features of the claim 1.

In a method for transmitting data in a radio frequency Identification system from a transponder to a reader Load modulation of a polling signal transmitted by the reading device, Wherein the transponder starts at the beginning of the reception of the interrogation signal Is initialized and responds with the transmission of the response signal First a predetermined number of not to the reply signal And then stored in Recursive sequence followed by the terminator sequence Response signal until the interrogation signal is interrupted.

By the predetermined number of non-reply signals Data bits, the time span which the reader is used to build up is bridged Of the query field. At the same time, the reader is switched to the clock of the Response signal. By the terminator sequence, which the Start of a valid response signal, this is already displayed at the First transmission correctly recognized by the reader.

The terminator sequence advantageously consists of a bit sequence, which in the Actual response signal can not occur. For example Sending the terminator sequence the interrogation signal for a duration of 1.5 Bit periods is unmodulated. Such a sequence can be found in the actual The answering signal does not occur and is therefore safe from the reader Detected. It is also possible to send the terminator sequence Interrogation signal for a duration of 1.5 bit periods. The time duration of 1.5 bit periods is important for reliable detection Can be reliably recognized as a terminator sequence by the reader.

As a predetermined number of non-reply signals A sequence of 3 to 10 logical ones is sent to data bits. Within this time, the interrogation signal has generally become so far In that the load-modulated response signal from the reading device Can be safely decoded.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.<dl tsize="7"><dt>FIG</dt><dd>Flowchart of the method; </dd><dt>FIG</dt><dd>Shows a terminator in data flow;</dd><dt>FIG</dt><dd>Shows a table showing the operating states to send Of the terminator.</dd></dl>

To avoid the above-mentioned problem, the transponder transmits At the beginning of data transfer, such as during initialization, some Non-relevant data bits, followed by a special data-type (Terminator), which is composed, for example, of sequences of 1.5 Bit periods. This will synchronize the reader and In addition, the terminator sequence is used to start a valid Data word is displayed, so that this is already present in the first transmission Correctly.

FIG. 1 shows a flow chart of the method. After this Reception of the interrogation signal generated by the reader, the Transponder, initialized. The initialization comprises, on the one hand, setting The communication paramenter as well as the transfer of the transponder into A defined initial state. The transponder then starts By means of load modulation of the interrogation signal, to the reader send. To give the reader sufficient time in a certain Frame to generate a constant interrogation signal, Decoding the data sent from the transponder to the reader Is required, the transponder first transmits a predetermined Number of data bits not belonging to the response signal. During this time, the reader is also switched to the answer signal Synchronized.

Subsequently, a terminator sequence is transmitted, which is thereby determined That it can not occur in the actual data flow. As A 3 bit long sequence has been found to be particularly advantageous The sampling signal being unmodulated for a duration of 1.5 bit periods. FIG. 2 shows a terminator in data flow. Besides the property that This sequence can not occur in the actual data flow They are characterized by the very short duration.

After the terminator sequence, the answer signal becomes the reader Posted. If the reader has recognized the terminator sequence, A very high probability of the answer signal immediately Decoded. Nevertheless, the answer signal is followed by one Terminator sequence as long as the transponder is sent to The interrogation signal is interrupted. Then either the Communication between the reader and the transponder Or the reader transmits data or commands to the transponder.

In the table of FIG. 3 are a series of operating states In which it is useful to send a terminator sequence To increase the effectiveness of data transmission. So it is next to the Initialization also at transition from write access to the Read access, after a write error, direct access, and Send a crypto response of advantage to the answer signal by the Terminator sequence.

Advantage: The data can be immediately correct at the first transmission be recognized. This results in a reduction in the duration of the Data transmission.