The Near Field Communication (NFC) market is emerging into multiple fields including medical, consumer, retail, industrial, automotive, and smart grid. Reader/Writer is one of the three operational modes supported by the TRF7970A. When using reader/writer mode the user can configure the TRF7970A to read Type 2, Type 3, Type 4A, Type 4B, and Type 5 tag platforms, also called transponders. The tags can store NFC Data Exchange Format (NDEF) messages or proprietary defined data.
This application report describes the fundamental concepts of reader/writer mode and how to properly configure the TRF7907A transceiver for each supported technology. Furthermore, it describes how to successfully activate, select, and read or write supported tags.
This application report and example firmware focuses on examples where the user presents only one tag at a time. However, it is possible from both a hardware and firmware standpoint to read multiple tags at the same time.
For applications that use only reader/writer mode, the TRF7964A can be used as a drop-in alternative to the TRF7970A.
Sample code described in this document can downloaded from http://www.ti.com/lit/zip/sloa227.
BoosterPack, LaunchPad are registered trademarks of Texas Instruments.
Arm, Cortex are registered trademarks of Arm Limited.
All other trademarks are the property of their respective owners.
ALL_REQ
NFC-A Polling command, equivalent to ISO14443-3 short frame command WupA (0x52)
ALLB_REQ
NFC-B Polling command, equivalent to ISO14443-3 command WupB
APDU
Application Protocol Data Unit, used in command-response pairs to exchange I (information), R (receive ready) or S (supervisory) blocks.
ATTRIB
PICC Selection Command, Type B
ATQA
Answer To ReQuest A, ISO14443-3 term, equivalent to NFC term SENS_RES
ATQB
Answer To ReQuest B, ISO14443-3 term, equivalent to NFC term SENSB_RES
CC
Capability Container, contains management data and is stored inside a read-only EF. This EF is located inside the NDEF tag application. Default (or basic) file ID for this file (for NFC) is 0xE103. See NFC Type 4 tag Operation Specification and ISO/IEC 7816-4 for more information.
CE
Card Emulation, one of the three modes offered by NFC devices. In this optional mode of NFC operation, an NFC Forum device is considered to be a card emulation platform only when it is emulating a Type 3, Type 4A or Type 4B tag platform. Emulation of any other cards or tags is outside the scope of the NFC Forum Brand Promise.
DEP
Data Exchange Protocol, an abstracted operational layer that is using either ISO or NFC protocols to exchange data. Thus, two terms can be created with this acronym: ISO-DEP and NFC-DEP. In the context of this document, after activation and selection of the emulated card and before deactivation, ISO-DEP is used exclusively to exchange data between reader/writer (PCD) and tag platform (PICC).
EF
Elementary File, a set of data objects, records or units sharing the same file identifier and the same security attributes
File Identifier
Two byte data element used to address a file
fc
Carrier frequency, in the context of NFC/HF RFID, is 13.56 MHz ±7 kHz. This is the fundamental transmit frequency of the reader/writer (also called PCD)
Initiator
Generator of the RF field and source of the beginning of the NFCIP-1 communication
MIME
Multipurpose Internet Mail Extensions
Modulation Index, m
Signal amplitude ratio of , where b is the ratio between the modulated amplitude and the initial signal amplitude. The index m is defined per protocol type for both downlink and uplink and is generally expressed as a percentage (for example, Type A uses m = 100%, and Type B uses m = 8 to 14%).
NDEF
NFC Data Exchange Format
NFC
Near Field Communication
PCB
Protocol Control Byte, used for conveying information required to control data transmission of blocks during the exchange of command-response APDU pairs. Bit coding of this byte and use rules are found in ISO/IEC FDIS 14443-4.
PCD
Proximity Coupling Device (also commonly referred to as reader/writer)
PICC
Proximity Integrated Circuit Card (also commonly referred to as tag, tag platform or transponder)
PUPI
Pseudo Unique PICC Identifier (randomly generated or static number returned by PICC as part of the response to REQB, WupB, ALLB_REQ or SENSB_REQ)
RTD
Record Type Definition
SAK
Select AcKnowledge (from ISO14443-3), in NFC terms this is also called SEL_RES
SDD_RES
Equivalent to ISO14443-3 response to SDD_REQ, and is complete NFCID1 CLn + BCC (if cascade level 1 (single size UID) or indicates NFCID1 is incomplete in the response and further cascade levels must be completed to obtain complete NFCID1+BCC.
SDD_REQ
Equivalent to ISO14443-3 Type A anticollision sequence. Comprised of SEL_CMD, SEL_PAR and n data bits coded based on cascade level specified by SEL_CMD and calculated by value of SEL_PAR
SEL_RES
Equivalent to ISO14443-3 SAK response
SENS_REQ
NFC-A Polling command, equivalent to ISO14443-3 short frame command REQ_A (0x26)
SENS_RES
NFC-A Polling Response, equivalent to ISO14443-3 ATQA
SENSB_REQ
NFC-B Polling command, equivalent to ISO14443-3 command REQ_B
SENSB_RES
NFC-B Polling command response, equivalent to ISO14443-3 ATQB
SENSF_REQ
NFC-F Polling command
SENSF_RES
NFC-F Polling response
Single Device Detection (SDD)
Algorithm used by the reader/writer to detect one out of several targets in its RF field (Type A anticollision, from ISO/IEC 14443-3)
T2T
Type 2Tag
T3T
Type 3Tag
T4T
Type 4Tag
T5T
Type 5Tag
Tag
See Tag Platform
Tag Platform
Responds to reader/writer (PCD) commands by using load modulation scheme (passive operation)
Throughout this document, the terms tag, tag platform, and transponder all have the same meaning.
TLV
Type Length Value
Transponder
See Tag Platform
UID
Unique IDentifier
VICC
Vicinity Integrated Circuit Card
The TRF7970A device supports three modes: reader/writer, card emulation, and peer-to-peer. This document describes how to use the TRF7970A in reader/writer mode. This mode allows an NFC enabled system to activate and read existing RFID and NFC tags. In the case of the TRF7970A, it is possible to read Type 2 (T2T), Type 3 (T3T), Type 4A or B (T4T), and ISO15693 (T5T) tag platforms. NFC transceivers supporting reader/writer mode typically poll to check if a tag or NFC peer is present every 500 ms. This time is known as the period time, which includes the time the transceiver is polling (searching for a tag) plus the time the transceiver is listening to be activated (in the case it is emulating a tag or is in peer-to-peer target mode). In Figure 1, for example, the transceiver is first polling for Active A and F technology (active peer-to-peer). Next, it polls for passive A technology (ISO14443A-3), passive B (ISO14443B-3), passive F (ISO18092), and then passive V (ISO15693).
For more information on active peer-to-peer communication and how passive A and F technology can be used to activate peer-to-peer communication, see NFC active and passive peer-to-peer communication using the TRF7970A.
The reader always generates the RF field and the tag load modulates the RF field to send their response. Figure 2 shows the NFC/RFID layers used to read and write tags. Both T2T and T4TAplatforms use technology ISO14443-3 (Type A) at an initial bit rate of 106 kbps for tag activation. T4TB platforms use technology ISO14443-3 (Type B) at an initial bit rate of 106 kbps for tag activation. After the activation process is completed, both T4TA and T4TB platforms use ISO7816-4 and ISODEP layers to read or write the tag content. After the T2T platform is activated it uses T2T commands to read or write the tag content. T3T platforms use technology ISO18092 at an initial bit rate of 212 kbps or 424 kbps for tag activation. When the T3T is activated it uses T3T commands to read or write the tag content. T5T platforms use technology ISO15693 for activation and to read the tag content.
A 16-bit and a 32-bit microcontroller were used to interface with the TRF7970A to demonstrate a reference example of the reader/writer mode. The firmware supports flexible functions that allow the user to enable or disable reading T2T, T3T, T4TA/B, and T5T platforms. Additionally, the firmware provides support for NFC-enabled smart phones that can emulate tag platforms. The firmware can activate and select NFC-enabled smart phones, allowing users to read card data by creating their own custom applications using existing APIs.
Table 1 lists the NFC/RFID technologies that the provided example firmware supports.
NOTE
Type 1 tags are not ISO compliant and require the use of Direct Mode 0 (DM0) to receive raw RF packets. Due to this, the firmware example does not support these tags.
Tag Technology | Support |
---|---|
Type 1 | ✗ |
Type 2 | ✓ |
Type 3 | ✓ |
Type 4A | ✓ |
Type 4B | ✓ |
Type 5 | ✓ |
NFC enabled systems can support both reader/writer mode and listen mode. To ensure that two NFC reader devices do not send commands at the same time, an initial RF collision detection is required. The transceiver must check the external received signal strength indicator (RSSI) value that measures the strength of the demodulated subcarrier signal before enabling its own RF field. If the RSSI value is greater than 0x00, it will not enable its RF field.
The relation between the 3-bit code and the external RF field strength (A/m) sensed by the antenna must be determined by calculation or by experiments for each antenna design. The antenna Q-factor, coupling factor between the two antennas and connection to the RF input influence the result. Figure 4 through Figure 6 provide the correlation of the free space distance between two unmodified TRF7970ATB modules and the 3-bit external RSSI value in three directions (see Figure 3 for more details on each orientation). One TRF7970A has its RF field at full power (+5 V), and the second TRF7970A is used to take RSSI measurements across different distances.
The initial RF collision can be accomplished by performing the following steps: