ST AN2399 Application note

AN2399

Application note

RFID library for SR176 tag management with STR71x

Introduction

This document describes a software and hardware RFID interface using the STR71x I2C
peripheral and the CRX14 RFID transceiver.

The main purpose of this software and hardware package is to provide resources to assist
the development of an application using an RFID tag.

The software interface is composed of library source files, include files and some application
template source files.

January 2008 Rev 1 1/22

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Contents AN2399

Contents

1 File organization of the RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Overview of radio frequency identification . . . . . . . . . . . . . . . . . . . . . . . 4

3 Operating ranges and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Close coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.2 Short range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.3 Long range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.4 Extended or very long range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 ISO standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.1 ISO compatibility for ST devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 ST short-range contactless memories . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1 SR176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.2 SRIX4K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.3 SRIX512 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

6 ST short range coupler: CRX14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

7 Overview of RFID reader using STR710 . . . . . . . . . . . . . . . . . . . . . . . . . 9

7.1 CRX14 demonstration kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

7.2 Interfacing with STR7xx using I2C peripheral . . . . . . . . . . . . . . . . . . . . . 12

8 RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8.1 RFID reader/writer: the application layer . . . . . . . . . . . . . . . . . . . . . . . . . 14

8.2 SR176 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.3 CRX14 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.4 I2C commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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AN2399 File organization of the RFID library

1 File organization of the RFID library

The following table presents the library modules:

Table 1. RFID library modules

File Description

Device_RFID.h RFID definitions, type definitions and function prototypes

Device_RFID.c Protocol management to interface the CRX14 transceiver

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Overview of radio frequency identification AN2399

2 Overview of radio frequency identification

Countless business applications, from product manufacturing to end-customer sales, can
benefit from radio frequency identification (RFID). With RFID, logistics becomes more
effective, stock handling is easier, traceability is guaranteed, cloning and counterfeiting can
be avoided, antitheft protection is enabled, and warranty problems can be easily eliminated.

What is radio frequency identification (RFID)?

RFID technology uses radio communications to uniquely identify items, such as goods,
people, or animals. It enables automated collection of information on identified items
independently from their position, without the need of a direct optical link or human
intervention. RFID also liberates the user from harsh or dirty environment concerns that
restrict other automatic identification solutions such as barcodes. On top of that, RFID is
used as a bi-directional data carrier since it allows information attached to the item to be
written and updated on the fly.

What does a RFID system consist of?

An RFID system consists of several components including one or multiple contactless
memory tags (or transponders), attached to the items to be labeled, identified, and traced,
and handheld or fixed contactless read/write reader station units or coupling devices
exchanging data with the transponder(s) by means of RF signals.

Contactless memory tags

Contactless memory tags (transponders) are the backbone of the RFID system since

they contain data that allow the items to be identified. A contactless memory tag is made of
a non-volatile memory associated with a radio frequency communication block, performing
RF signal modulation, demodulation, power supply regulation, and an antenna. A
transponder can be read-only (ROM), one-time-programmable (OTP), or read/write
(EEPROM), and it can be embedded in various package formats (inlays, cards, etc.).

The reader

The reader (or reader station unit) is connected to an antenna that transmits and receives
the radio frequency signal from and to the transponder(s). The reader sends an RF signal to
the transponder’s antenna. This signal generates a voltage that is rectified and provides a
power source to the transponder. The power transfer from the reader to the transponder is
performed through an inductive coupling between the two coils in 125 kHz and 13.56 MHz
systems. For ultra-high frequencies (UHF), the electric field generated by the reader is used
to power the tag. In other words, the transponder does not need a dedicated power supply.

Passive and active tags

Two main families of transponders exist: Passive (battery-less) and Active. Adding a battery
can bring several advantages, such as improvement of the reading range or continuous
monitoring of temperature and pressure etc., but adds an extra cost. During the reader­transponder communication, the RF signal generated by the reader is modulated according
to the data to be sent. In the transponder-reader direction, no modulation is applied on the
reader RF signal and the communication is done through load modulation in inductive
coupling systems. The reader interfaces with the RFID system control host through a serial
interface such as RS232, RS422/485, or USB.

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AN2399 Operating ranges and applications

3 Operating ranges and applications

The RFID operating ranges are defined by the distance between the transponder(s) and the
reader.

3.1 Close coupling

The close-coupling range includes the transponder-reader distances up to 5 cm. Brand
protection, anti-counterfeiting of electronic goods and food consumables, as well as
electronic purchases at vending machines operate in the close-coupling range. These
applications employ low-cost readers operating with a limited number of transponders and
require security features such as password, anti-clone, or cryptographic capabilities.

3.2 Short range

In addition, RF technology systems are a universal solution for various ticketing applications,
regardless of the means of transport used (public transportation or private car). Contactless
systems can also be used in a wide range of access-control applications, including entrance
systems to and within public buildings (in offices, for example), time and attendance
systems, room logistics at hotels, locking systems, and amusement parks. These short-
range or proximity-range applications use low-cost transponders embedded in plastic cards
or paper tickets and operate in the range up to 20 cm. Readers and transponders from
different suppliers must be fully interoperable. Required security levels are satisfied through
password, anti-clone, or cryptographic capabilities.

3.3 Long range

RF transponders are a low-cost universal solution for tracking a wide variety of valuable
assets (e.g. package delivery, animal tracking) and improving the product supply chain
management from manufacturing to stock handling to distribution. Capable of storing
traceability history, transponders provide accurate real-time information on each tagged
item. Similarly, they can be used for anti-theft applications (using Electric Article
Surveillance) or access control from a longer distance.

These long-range or vicinity-range applications operate within 1 m from the reader and
typically involve a large number of low-cost transponders (100+), requiring reliable anti­collision mechanisms and transponder-reader interoperability.

3.4 Extended or very long range

Extended or very long-range (up to 10 meters) RFID systems will be instrumental in creating
low-cost contactless solutions for new supply chains, logistics, and tracking applications that
can offer improved efficiency, accuracy, and security standards to major manufacturers,
retailers, and their customers.

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ISO standards AN2399

4 ISO standards

The ISO organization devotes itself to definition and promotion of worldwide-recognized
standards in the contactless area. 3 standards for objects operating in the 13.56 MHz
frequency range have already been approved (ISO SC17 on identification cards and related
devices):

● ISO10536 identification cards and contactless integrated circuits cards:

– Close-coupling cards (reading range below 2 cm).

● ISO 14443 identification cards and contactless integrated circuits cards:

– Proximity cards (reading range up to 20 cm).

● ISO 15693 identification cards and contactless integrated circuits cards:

– Vicinity cards (reading range up to 1 m).

This standard is part of the future SC31/ISO18000 standard, currently under
discussion.

ISO standards are recognized worldwide and guarantee the full interoperability of
transponders and readers from different suppliers.

4.1 ISO compatibility for ST devices

ST contactless memories are ISO-compatible:

● ISO 14443 type B for short-range devices

● ISO 15693 or ISO18000-3 Mode 1 for long-range devices.

This application note refers to ST ISO 14443B short range RFID.

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AN2399 ST short-range contactless memories

5 ST short-range contactless memories

5.1 SR176

ST’s SR176 is an ISO14443 Type B device. It offers 176 bits of EEPROM organized in
eleven 16-bit blocks, a 64-bit UID and an 8-bit Chip_ID. Targeted markets are cost-sensitive
applications such as industrial identification, access control, and low-value tickets that do
not need to be modified more than a few times.

5.2 SRIX4K

ST’s SRIX4K includes 4096 bits of non-volatile memory organized in three areas: the first
area is an OTP (One Time Programmable) bit zone, in which bits can only be switched from
1 to 0; the second area provides two 32-bit binary down counters; and the last area which is
a non-volatile memory split into 32-bit blocks (9 blocks are lockable). The SRIX4K supports
France Telecom’s proprietary anti-clone function and anti-collision mechanism based on an
8-bit Chip_ID.

The SRI4K is based on the SRIX4K, excluding the support of France Telecom’s proprietary
anti-clone function.

5.3 SRIX512

The SRIX512 is a light version of the SRIX4K with 512 bits of non-volatile memory. All three
devices (SRIX4K, SRI4K, SRIX512) are designed for short-range applications such as
consumable products identification, anti-counterfeiting, or high-end ticketing solutions.

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