Radio frequency identification technologies (RFID) have continuously called engineers and managers attention for many identification and goods tracking applications. Its contactless operation and the ability to be embedded inside goods during manufacturing, or inside plastic cards, tokens and capsules, have enabled RFID tags to be identified as the natural replacement technology for magnetic stripe cards in mass transportation, contact memory cards in personal identification, and barcodes in goods inventory and airport baggage control.
This long lasting promise has not been fulfilled, but nevertheless RFID devices and tags have become ubiquitous and its application areas are being further extended and complemented with the advent of new technologies and standards like near-field communications (NFC).
Due to NFC’s popularity increase, most mobile phone manufacturers are currently delivering products which incorporate NFC interfaces and OS support APIs for implementing RFID and NFC enabled applications. As an example, the Android OS 4.4 (KitKat) version has included host card emulation for emulating tags working according to ISO14443-4 air interface (HF RFID, proximity cards) for exchanging command-response APDUs as defined by ISO7816-4.
HF RFID and NFC are becoming enabling technologies in the new world of smart metering. Current status information, partial and complete log records, calibration data and parameters, and other internal meter data and information can be made externally accessible by means of the NFC interface. Several manufacturers have already envisioned this type of RFID application and provide solutions that could be grouped in three main approaches or variants: Serial Memory with RFID/NFC Interface, RFID/NFC interface to EEPROM memory interface, and RFID/NFC Transceiver for implementing Card Emulation (CE).
Dynamic RFID/NFC Tags
With almost no previous RFID/NFC knowledge required and just one chip and a few passive components, the serial memory with RFID/NFC interface solution is the easiest to integrate in hardware and the one requiring less lines of firmware code. The analog front-end (AFE), the RFID/NFC protocol and commands execution engines, and the non-volatile memory are packaged together with the MCU interface engine (see Figure 1). The application software developer only needs to concentrate on keeping the non-volatile memory content up to date and processing a minimum set of events from the AFE, like RF detection or read/write indication flags when memory is accessed from the RFID interface. This kind of RFID/NFC enabling solution is also sometimes referred to as Dynamic RFID/NFC Tag.
Several dynamic RFID/NFC tag options are available from ST Microelectronics (STM), Atmel, and Texas Instruments (TI), some of them provide built-in to support for handling NFC Data Exchange Format (NDEF) messages and records. STM’s M24LR and M24SR series implement air interfaces according to ISO standards ISO15693 and ISO14443-Type A, respectively, with I2C MCU interface. TI’s RF430CL330H and TMS37157, on the other side, implement air interfaces according to ISO standard ISO14443-Type B and 134.2 kHz LF interface, respectively, with SPI MCU interface. Working in the 125 kHz low frequency (LF) band, the AT24RF08 asset identification EEPROM from Atmel provides 8K bits of EEPROM and an SPI MCU interface.
Dynamic RFID/NFC Tags exhibit a great level of integration simplicity, but it comes at the cost of providing only a rather reduced air interface commands set and very limited security support.
RFID/NFC to EEPROM Memory Interface
Not as easy to integrate as dynamic RFID/NFC tags, but more flexible in terms of memory size, the RFID/NFC to EEPROM memory interface integrates the analog front-end (AFE) with the RFID/NFC protocol, the commands execution and the serial EEPROM memory interface engines (see Figure 2).
Within this category, Atmel provides the AT88RF001 RFID External EEPROM interface IC which implements the air interface according to ISO14443-2 Type B.
Unfortunately, sine no independent MCU interface is provided by this EEPROM interface IC, it is up to the designer to implement some sort of EEPROM SPI port multiplexing in order to gain read/write access to it from the MCU. As another limitation, memory access security is implemented using a simple four-byte password passing command mechanism, with no mutual authentication and clear plain text communication.
RFID/NFC Transceiver for Card Emulation
RFID/NFC transceivers constitute the most flexible NFC enabling solution for smart metering and other applications, but that solution comes at the cost of requiring a deeper RFID/NFC knowledge and a more complex firmware design. There are several different variants sharing a common setup which includes the analog front end, a protocol engine for simplifying some RFID/NFC protocol communication tasks and an MCU interface for exchanging command/response APDUs, as shown in Figure 3.
Currently several manufacturers provide complete solutions, including reference hardware designs and complete software libraries. TI’s TRF7970A Multi-Protocol Fully Integrated 13.56-MHz RFID/NFC Transceiver IC, NXP’s PN512 NXP NFC transceiver and NXP's PN544 NFC Controller, Sony’s RC-S801/802/926 NFC Dynamic Tag (FeliCa Plug), and Austria MicroSystems’s (ams) AS3953 NFC Interface constitute representative examples within this category. Some of these devices, like the aforementioned from TI and NXP, also provide support for operating in reader mode.
Implementing card emulation is not an easy task, because it imposes many challenges in terms of standards compliance and interoperability. It does however give the designer enough freedom for implementing security mechanisms up to the highest required standards and an almost limitless platform for data, commands, and parameters interchange.
Are you currently working on a NFC enabled device or equipment? Have you found any advantage in using RFID/NFC with respect to other wireless technologies?