Near-field communication

Abstract

A method of operating a near-field communication, NFC, tag, is disclosed. The method comprises after an NFC reader performs a first NFC Data Exchange Format, NDEF, read (53) of the NFC tag, the NFC ta

Description

Field The present invention relates to near-field communication. Background Near Field Communication (NFC) Forum tags (herein referred to simply as "NFC tags") can be used in a variety of different applications including access control, identification, payment, and inventory tracking. Data can be exchanged between an NFC tag and an NFC-enabled reader, such as a smartphone, using the NFC Data Exchange Format (NDEF) protocol. Under the NDEF protocol, a message stored in an NFC tag can be dynamically modified by a host, such as a microcontroller, to provide additional information, such as a value of a sensor measurement. Application note AN5439 Rev 3 "Augmented NDEF with ST25DV-I2C series Dynamic NFC Tags", May 2021 describes enhancing the performance of ST25DV-I2C series Dynamic NFC Tag ICs, for instance appending data (such as sensor values) dynamically to an NDEF message. Although there are advantages to automatically updating NDEF message content, the approach faces timing constraints. After a phone detects the presence of a tag, it begins emitting a continuous RF field after which there is a delay before anti-collision starts. The delay (which is at least 30 milliseconds and typically no more than 40 milliseconds) allows the host to update NDEF message content in tag memory. Once anti-collision has finished, the phone can start an NDEF read procedure. If, however, the tag does not respond, the phone aborts the procedure and stops emitting the RF field. A battery-less tag is able to harvest energy from the continuous RF field to power itself and the host thereby enabling the host to perform an NDEF message update. This, however, leaves little time for performing the message update. Moreover, the narrow time window also restricts what other operations can be successfully completed before anti-collision starts, such as taking and storing measurements. Summary According to a first aspect of the present invention there is provided a method of operating a near-field communication, NFC, tag. The method comprises, after an NFC reader performs a first NFC Data Exchange Format, NDEF, read of the NFC tag, the NFC tag causes the NFC reader to perform a second NDEF read of the NFC tag. This can help to relax timing constraints imposed by NDEF content update by allowing the NFC tag to store variable data, such as sensor measurement, in an NDEF message after an NDEF read, ready for another NDEF read. Causing the second NDEF read may comprise causing the NFC reader to stop transmitting a continuous RF signal. Thus, after the NFC reader disconnects from the tag, the NFC reader can perform tag detection and then the second NDEF read during which it receiving the variable data. Causing the second NDEF read may comprise being unresponsive to polling by the NFC reader. The NFC tag may be unresponsive for a minimum time, for example, at least 500 ms. This may cause the NFC reader to disconnect from the NFC tag. The NFC tag may comprise NFC tag circuitry, which includes non-volatile memory, and a host controller. Causing the second NDEF read may comprise the host controller causing the NFC tag circuitry to cause the tag reader to perform second NDEF read of the NFC tag. The method may comprise the host controller causing a write conflict to the non-volatile memory. The method may comprise the host controller configuring the NFC tag circuitry to be being unresponsive to polling by the NFC reader. The method may further comprise harvesting energy from an RF signal received from the NFC reader and providing power from the harvested energy to a host controller. The method may further comprise, in the first NDEF read, in response to receiving a first NDEF read command from the NFC reader, transmitting an NDEF message to the NFC reader. The method may further comprise, after the first NDEF read, storing the variable data in the NDEF message in non-volatile memory in the NFC tag. The variable data may include at least one value of a measurement from a sensor, such as a photodiode. The variable data may include a plurality of values, each value corresponding to a respective measurement at a respective time. The host controller may be a microcontroller. According to a second aspect of the present invention there is provided a method of operating a near-field communication, NFC, reader, which comprises an NFC interface, a controller, an wireless network interface and a display, the method comprising performing a first NFC Data Exchange Format, NDEF, read of an NFC tag, contacting a remote server using an URL obtained by the first NDEF read, receiving instructions from the remote server, presenting the instructions to a user, performing a second NDEF read of the NFC tag, and forwarding variable data obtained by the second NDEF read. The method may further comprise, responsive to the tag, after performing the NDEF read and before performing the second NDEF read of stopping transmitting the continuous RF signal and performing tag detection. According to a third aspect of the present invention there is provided a near-field communication, NFC, tag configured such that, after an NFC reader performs a first NFC Data Exchange Format, NDEF, read of the NFC tag, the NFC tag causes the NFC reader to perform a second NDEF read of the NFC tag. The NFC tag may comprise NFC tag circuitry including an energy harvesting module for harvesting energy from an RF signal received from an NFC reader, an NFC protocol unit, non-volatile memory for storing an NDEF message, and a host controller. The energy harvesting module may be configured to provide power from the harvested energy to the host controller. The NFC tag may be battery-less. The NFC tag may further comprises a sensor for providing variable data for transmission in an NDEF message. The host controller may be a microcontroller. The NFC tag circuitry may comprise an integrated circuit chip. The NFC tag circuitry and host controller may be integrated, for example, in an integrated circuit chip or in an electronic circuit printed on a substrate. The tag may be a diagnostic testing device, such as a lateral flow device. The NFC reader may be a mobile communications device, such as a smartphone or tablet. The NFC reader may be a wearable computing device. Brief Description of the Drawings Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of an NFC tag system comprising an NFC tag, a second device which includes an NFC reader and a remote server; Figure 2 is a more detailed schematic block diagram of the NFC tag and NFC reader shown in Figure 1; Figure 3 illustrates activity of an NFC tag; Figure 4 is a process flow diagram of a method of operating the NFC reader shown in Figure 1; Figure 5 is a process flow diagram of a method of operating the NFC tag shown in Figure 1; and Figure 6 is a sequence diagram showing exchange of data between the NFC tag and NFC reader and the server shown in Figure 1. Detailed Description of Certain Embodiments Tag system 1 Referring to Figure 1, a Near Field Communication (NFC) tag system 1 is shown. The tag system 1 comprises an NFC tag 2 (herein also referred to simply as a "tag"), which contains NFC tag circuitry 3, and an NFC reader 4 (herein also referred to simply as a "reader" or "NFC-enabled device"), which includes an NFC reader circuitry 5 (herein also referred to as an "NFC interface"). The NFC tag circuitry 3 and the NFC reader IC 5 are able to communicate via a radio frequency (RF) wireless link 7. The NFC reader 4 is able to communicate with a remote server 8 via a computer network 9, which can include the Internet. The NFC tag 2 can take the form of a diagnostic testing device and the NFC reader 4 can take the form of a smartphone, tablet, or other mobile communications device, or a wearable computing device. The tag 2 and reader 4 can exchange data via NFC protocols, and the reader 4 can retrieve data and / or forward data to and from the remote server 8. For example, the reader 4 can transmit commands 10 to the tag 2. The tag 2 can transmit an identifier 11, for instance in the form of a uniform resource identifier (URI), to the reader 4 identifying the location of the remote server 8. The remote server 8 may, in turn, transmit instructions 12 to the reader 4 which can be presented to a user, for instance, regarding what to do with the tag 2 and / or the reader4. The tag 2 is able to transmit measurement values 13, for example values of light intensity, to the reader 4, which in turn can forward these to the server 8. The reader 4, server 8 or another server (not shown) can process the measurement values 13 which may result in a determination 14 (or "result"), for instance, a diagnostic test result, which can be transmitted to the reader 4 to be presented to the user. The tag circuitry 3 takes the form of a Type 4 Near Field Communication (NFC) Forum tag IC, such an STMicroelectronics ST25DV-I2C tag IC chip, or other circuity which is able to support reading and writing of NFC Data Exchange Format (NDEF) messages. The tag circuitry 3 need not take the form of a single IC chip. For example, the tag circuitry 3 may be provided, at least in part, by printed electronics. The reader circuitry 5 correspondingly supports communication with the tag circuitry 3, and may take the form of an NFC transceiver IC chip. Referring to Figure 2, the tag 2 and reader 4 are shown in more detail. The tag 2 includes an antenna 21, for example, in the form of coil operatively connected to the inputs of the tag circuitry 3. The tag circuitry 3 includes an analogue front end (AFE) 22, a power management unit 23 (or "energy-harvesting circuit"), a digital unit 24 (or "protocol engine" or "core") for suitably formatting data and modulating a signal for transmission by the antenna 21 and suitably converting and demodulating a signal received by the antenna 21 into data packets, a host interface 25, non-volatile memory 26 for example in the form of EEPROM which stores an NDEF message 27 (which may be referred to as an "Internet Link" of "URI NDEF record"), and a set of registers 28, for instance, static configuration registers and dynamic configuration and status registers. Non-volatile memory 26 may take the form of flash memory or other memory capable of retaining data for many years. In some examples, however, non-volatile memory may retain data for a much shorter period, but long enough to keep data between tag / tag-reader sessions, for instance, between 1 second to 5 minutes (300 seconds). The tag 2 includes a host controller 30 (or "host processor"), for example, in the form of a microcontroller, operatively connected to the tag circuity 3 via a bus 31, for example, in the form of an Inter-Integrated Circuit (I2C) bus. The host controller 30 may include, or be provided with, one or more digital-to-analogue converters 32 (although this can be avoided by using a digital output and PWM techniques) and / or one or more analogue-to-digital converters 33. The tag 2 may include one or more drivers 34 for driving one or more actuators 35, such as one or more light-emitting diodes. The tag 2 may include one or more sensors 36, such as one or more photodiodes, and one or more amplifiers 37 for amplifying signals from the one or more sensors 37. The tag 2 does not have a battery (in other words, it is battery-less) obtaining power from the power management unit 23. In some cases, the tag 2 may include a shortterm energy storing-capacitor (not shown) for storing harvested power. For example, the capacitor (not shown) may be charged for a given period of time, for example, between 10 seconds and 5 minutes or more (for instance, between the start of a diagnostic test and a device read time) and the energy stored in the capacitor (not shown) can be used by the tag 2 for providing power during measurement, processing and / or transmission. The NFC reader 4 includes an antenna 41, for example, in the form of coil operatively connected to the inputs of the reader circuitry 5. The tag reader 4 includes a controller 42, one or more wireless network interfaces 43 (for example, a mobile phone network interface and a wireless LAN network interface) via which the tag reader 4 can exchange data with the server 8 (Figure 1), and a display 44 which may take the form of a touchscreen, which can be used to present instructions to a user. The tag reader 4 includes other circuitry, components and parts, such as, among others, a microphone, speaker, buttons and a battery which are not shown for clarity. As explained earlier, the NFC reader 4 can take the form of a smartphone. The device controller 42 does not run any dedicated application software for controlling the NFC reader circuitry 5. Thus, any NFC-enabled smartphone can be used without modification and without installing software, although a user may be asked by the phone to grant permissions, such as allowing the opening of a web browser in response to receiving an NDEF message. Operation The present invention is based on the insight that the steps of performing sensor measurements, writing the values of sensor measurements to tag memory, reading those values from tag memory and transmitting the values to the tag reader need not all occur in the narrow time window between tag detection and the start of anti collision. Instead, sensor measurements can be performed, and sensor values can be written to tag memory, after an initial read operation is carried out. The tag then causes the tag reader to perform another, later read operation during which the sensor measurements are transmitted. Another read operation can be caused by the tag failing to reply to the tag reader or to reply with an error thereby resulting in the tag reader initiating tag detection anew. For example, in some cases, this can be achieved by the tag intentionally staying silent. Alternatively, the host controller can purposely cause a write conflict or other error. Referring to Figures 1 to 5, operation of the tag 2 and the tag reader 4 will now be described. The reader circuitry 5 starts tag detection by emitting a short, unmodulated RF pulse 51 to detect the presence of objects in the RF field (step SI). If the tag reader 5 detects the tag 3 (step S2), it starts technology detection by emitting a continuous RF field 52 (step S3). The tag circuitry 3 harvests the energy of the continuous RF field 52 which provides power to the tag circuitry 3 and the host controller 30. After a delay T of between about 30 and 40 ms (step S4), the reader circuitry 5 performs a first NDEF read operation 53 of tag memory 26 (step S5). The tag 2 waits for a request 54 (step S6) and upon receiving a read request 54 retrieves the NDEF message 27 from tag memory 26 and transmits the NDEF message 27 to the tag reader 4 (step S7). The first NDEF read operation 53 returns NDEF message 27 containing a URL which is used to identify and contact the server 8. Initially, the tag memory 26 does not contain any valid sensor values. After the reader circuitry 5 has read tag memory 26, the tag 2 remains powered and performs one or more sensor measurements 56 (step S8). Specifically, the host 30 performs the sensor measurement(s) 56 by reading values 13 from the sensor 36. The host 30 writes the sensor values 13 as variable data into the payload of one or more NDEF records (not shown) of NDEF message 27 in tag memory 26 (step S9), in other words, it modifies the NDEF message 27. The last value written is an authentication value 58 containing a checksum (step S10). Once the memory write is complete, the tag 2, in particular the host 30, causes the tag reader 4 to perform another NDEF read operation 53. In this case, the tag 2 triggers another NDEF read operation 53 by failing to reply to the tag reader 5 (steps Sil, S12 &SI) thereby resulting in the tag reader circuitry 5 stopping emitting the RF field 52 (step S14) and initiating a new round of tag detection. The host 30 can achieve this by suitably setting the tag registers 28. Shortly after the reader circuitry 5 stops emitting the RF field 51, the tag reader circuitry 5 starts tag detection, once detected and technology detection completed, another read operation is performed (steps SI to S5). This time, however, a second NDEF read operation 53 returns an NDEF message 27 containing sensor values 13 (steps S6 &S7). As will be explained hereinafter, the reader circuitry 5 can pass these values 13 to the device controller 42 which can then transmit these values 13 to the remote server 8. The host processor 30 can perform measurements and store sensor values in the same way as the previous cycle 59i (steps S8 to S10), and once the memory writing operation is completed, trigger yet another NDEF read operation 53. Normally, however, only two cycles 59i, 59? (or "sessions") involving two read operations 53 are needed. The process can be terminated by the tag 2 and the reader 4 being separated by a sufficiently large distance (typically, a few centimetres) that the tag 2 is no longer able to harvest power, loses power and is unresponsive to the reader circuitry 5. Once the reader circuitry 5 no longer detects the tag circuitry 3, the tag reader 5 stops emitting the RF field 52. This can occur at any point during the procedure, for example, during measurements or during the write procedure. Final removal of the tag 2 partway through a NDEF memory write 57 is likely to leave the message 27 in the NDEF memory 26 with an invalid checksum. This, however, is not a problem since the invalid checksum can be used to reject an invalid message. Diagnostic testing service Referring again to Figure 1, the tag reader 4 may be used to collect measurements from the tag 2. The measurement, however, can be processed by a remote server 8. Referring to Figure 6, operation of the tag 2, the tag reader 4 and the server 8 will now be described. In a first NDEF read operation, the tag reader 4 can send an NDEF read command 54 to the tag 2 which returns an initial NDEF message 27 containing the URL 11 of the server 8 (steps S101 &S102). The tag reader 4 extracts the URL 11 from message 27 (step S103) and sends a request 60 to the server 8 (step S104). The server 8 returns instructions 12 (step S105) which are presented to the user on the display (step S106). The instructions 12 may include steps that the user needs to carry out, such as brining the two devices 2, 4 together and, later, separating them, as well as information, such as a timer displaying countup or countdown time. In a second NDEF read operation, the tag reader 4 can send an NDEF read command 54 to the tag 2 which returns a modified NDEF message 27 containing sensor values 13 (steps S107 &S108). The tag reader 4 may extract the sensor values 13 from message 27 (step S109). The tag reader 4 sends the values 13 to the server 8 (step S110). For example, it may simply forward the message 27 containing the sensor values 13. In some cases, the message 27 containing the sensor values 13 may be encapsulated in a data container (not shown). The server 8 processes the measurements 13 to obtain a result 14 (step Sill) and can transmit the result 14 back to the tag reader 4 for presenting to the user. Further sessions, for example, a third and fourth session can be performed using the same tag reader 4 or another, different tag reader (not shown). It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known in the design, manufacture and use of NFC tags and NFC-enabled devices and component parts thereof and which may be used instead of or in addition to features already described herein. Features of one embodiment may be replaced or supplemented by features of another embodiment. The tag 2 may be or be associated with (for example, attached to) an article in a 5 manufacturing line. Thus, the tag 2 may be reflect the status of manufacture of the article and be updated as it proceeds along the manufacturing line, and the status can be read using readers located along the manufacturing line. Although claims have been formulated in this application to particular combinations of 10 features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present 15 invention. The applicants hereby give notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom

Claims

1. A method of operating a near-field communication, NFC, tag, the method comprising:■ after an NFC reader performs a first NFC Data Exchange Format, NDEF, read of the NFC tag, the NFC tag causing the NFC reader to perform a second NDEF read of the NFC tag.

2. The method of claim 1, wherein causing the second NDEF read comprises:- the NFC tag causing the NFC reader to stop transmitting a continuous RF signal.

3. The method of claim 1 or 2, wherein causing the second NDEF read comprises:- the NFC tag being unresponsive to polling by the NFC reader.

4. The method of claim 1, 2 or 3, wherein the NFC tag comprises NFC tag circuitry, which includes non-volatile memory, and a host controller and wherein causing the second NDEF read comprises:- the host controller causing the NFC tag circuitry to cause the tag reader to perform the second NDEF read of the NFC tag.

5. The method of claim 4, wherein the host controller causing the NFC tag circuitry to cause the NFC tag reader to perform the second NDEF read of the NFC tag comprises:- the host controller causing a write conflict to the non-volatile memory.

6. The method of claim 4 or 5, wherein the host controller causing the NFC tag circuitry to cause the NFC tag reader to perform the second NDEF read of the NFC tag comprises:- the host controller configuring NFC tag circuitry to be being unresponsive to polling by the NFC reader.

7. The method of claim 1 or any one of claims 2 to 6, further comprising:■ harvesting energy from an RF signal received from the NFC reader and providing power from the harvested energy to a host controller.

8. The method of claim 1 or any one of claims 2 to 7, further comprising, in the first NDEF read:■ in response to receiving a first NDEF read command from the NFC reader, transmitting an NDEF message to the NFC reader.

9. The method of claim 8, further comprising: ■ after the first NDEF read, storing the variable data in the NDEF message in non-volatile memory in the NFC tag.

10. The method of claim 1 or any one of claims 1 to 9, wherein the variable data includes at least one value of a measurement from a sensor.

11. The method of claim 10, wherein the variable data includes a plurality of values, each value corresponding to a respective measurement at a respective time.

12. The method of claim 1 or any one of claims 1 to 11, wherein the host controller is a microcontroller.

13. A method of operating a near-field communication, NFC, reader, which comprises an NFC interface, a controller, an wireless network interface and a display, the method comprising:■ performing a first NFC Data Exchange Format, NDEF, read of an NFC tag;■ contacting a remote server using an URL obtained by the first NDEF read;■ receiving instructions from the remote server;■ presenting the instructions to a user;■ performing a second NDEF read of the NFC tag; and■ forwarding variable data obtained by the second NDEF read.

14. The method of claim 13, further comprising:■ responsive to the tag, after performing the NDEF read and before performing the second NDEF read, stopping transmitting the continuous RF signal and performing tag detection.

15. A near-field communication, NFC, tag configured such that, after an NFC reader performs a first NFC Data Exchange Format, NDEF, read of the NFC tag, the NFC tag causes the NFC reader to perform a second NDEF read of the NFC tag.

16. The NFC tag of claim 15, comprising:■ NFC tag circuitry including:- an energy harvesting module for harvesting energy from an RF signal received from an NFC reader;- an NFC protocol unit; and non-volatile memory for storing an NDEF message; and■ a host controller;wherein the energy harvesting module is configured to provide power from the5 harvested energy to the host controller.

17. The NFC tag of claim 16, further comprising:■ a sensor for providing variable data for transmission in an NDEF message.10 18. The NFC tag of claim 16 or 17, wherein the host controller is a microcontroller.

19. The NFC tag of claim 16, 17 or 18, wherein the NFC tag circuitry comprises anintegrated circuit chip.15 20. The NFC tag of claim 16 or any one of claims 17 to 19, wherein the NFC tagcircuitry and host controller are integrated.15

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