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RFID library for SR176 tag management with STR71x

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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
www.st.com

Contents

AN2399

Contents
1 2 3 File organization of the RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Overview of radio frequency identification . . . . . . . . . . . . . . . . . . . . . . . 4 Operating ranges and applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 3.2 3.3 3.4 Close coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Shor t range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Long range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 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 5.2 5.3 SR176 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 SRIX4K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 SRIX512 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

6 7

ST short range coupler: CRX14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Overview of RFID reader using STR710 . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1 7.2 CRX14 demonstration kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Interfacing with STR7xx using I2C peripheral . . . . . . . . . . . . . . . . . . . . . 12

8

RFID library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1 8.2 8.3 8.4 RFID reader/writer: the application layer . . . . . . . . . . . . . . . . . . . . . . . . . 14 SR176 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 CRX14 commands layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 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.
File Device_RFID.h Device_RFID.c

RFID library modules
Description RFID definitions, type definitions and function prototypes Protocol management to interface the CRX14 transceiver

3/22

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 shortrange 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). Proximity cards (reading range up to 20 cm). Vicinity cards (reading range up to 1 m). ISO 14443 identification cards and contactless integrated circuits cards: ISO 15693 identification cards and contactless integrated circuits cards: 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.

6/22

AN2399

ST short-range contactless memories

5
5.1

ST short-range contactless memories
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.

7/22

ST short range coupler: CRX14

AN2399

6

ST short range coupler: CRX14
The CRX14 is a short-range contactless chip coupler compliant with the ISO14443 type B standard. It interfaces with the host CPU that manages the communications protocol in both directions through the industry-standard I²C serial bus. The coupler is equipped with France Telecom's proprietary anti-clone function and anti-collision mechanism. The CRX14 is supplied in SO16N packages. A complete solution combining the CRX14 coupler and SRxx transponders operates in the short range and ensures a total compatibility in terms of memory tag protocol access. In addition, the combination of the CRX14 and SRIX512 or SRIX4K memories guarantees a high level of system security for short-range and low-cost applications. Optimized for interoperability, these products can also work independently, with any ISO-standard chips. The CR14 is based on the CRX14, excluding the support of France Telecom's proprietary anti-clone function.

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AN2399

Overview of RFID reader using STR710

7

Overview of RFID reader using STR710
The RFID reader is developed using the STR710 ARM7TDMI powered microcontroller and the CRX14 low cost contactless coupler chip. Communication between the microcontroller and the coupler is achieved by an I2C bus. The RFID library has been developed to support SR176 tag. As depicted in picture below, the RFID library has been developed on a 4-layer structure. Using the application layer, the tag may be used as an EEPROM with read/write operation. It is not necessary to know how STR710 communicates with the CRX14 coupler chip and how CRX14 communicates with SR176 tag. Figure 1. Architecture details
RF - ASK Mod

STR710

I2C

CRX14

RF-BPSK mod

Tag

Firmware specifications RFID firmware for STR710 supports SR176 tag Firmware is developed on a 4 layer structure:
RFID reader/writer SR176 Commands CRX14 Commands I2C Commands Application layer: applications dedicated functions RF Commands layer: Initiate(), Select(), Completion(), GetUID(), Read_Block(), Write_Block() Transceiver Commands layer: CRX14 registers management I2C Bus layer: I2C protocol to interface CRX14

7.1

CRX14 demonstration kit
A demonstration kit has been created to interface CRX14 with the STR710 microcontroller via I2C. Further details can be found in the application note AN1806. The demonstration kit schematic and layout are shown below.

9/22

SDA

J1 FL5 0R FL4 0R 0R FL6 VCC 4 3 2 1

SCL

10/22

Figure 2.

D1 1N4148 (OP T IONAL) C6 VCC 100nF50V C8 100pF50V C5 10pF50V R8 0R ANT 1

Overview of RFID reader using STR710

VCC

OP T OP T C3 C1 7pF50V R5 X1 13. 56MHz C8' 8pF50V

R1

OP T

R3

E0 0R E2 0R R6 CRX14 C2 7pF50V

CRX14 demonstration kit schematic

R2

E1 0R

C7 120pF50V

C7' 33pF50V

R4

WURT H 742-792-042 U 1 FL7 1 VCC Vref 2 RF IN R F O U T 22nF50V 3 GND_RF E0 4 OSC1 E1 5 OSC2 E2 6 GND GND_RF 7 SCL GND 8 GND SDA 16 15 14 13 12 11 10 9

R7 0R

ANT 2

+ C4 22uF 10V

ai08488B

AN2399

AN2399 Figure 3. CRX14 demonstration kit layout

Overview of RFID reader using STR710

ai08489

ST has designed the CRX14, a short range contactless coupler chip, compliant with the ISO14443 type B proximity standard. The CRX14 generates a 13.56 MHz signal. Designed to deliver an RF power of 100 mW, it operates in the Short Range on contactless memory tags (provided that they, too, are compliant with ISO14443 type B). The CRX14 features the ST anti-collision mechanism, which allows the reader to detect and identify all the tags that are present in the operating range, and to access them individually. Because the CRX14 implements the France Telecom-proprietary anti-clone function, the reader can also perform authentication of tags that are equipped with the France Telecom anti-clone capability. The CRX14 coupler interfaces between:

the memory tags, on one side, through input/output buffers and the ISO14443 type B radio frequency protocol, and the system master processor, on the other side, through a 400 kHz I2C bus.

Operating from a 5 V power supply, and delivered in a SO16N package, the CRX14 coupler chip is an excellent solution for building contactless readers, embedded in the final equipment, and offering a good compromise between operating range and cost.

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Overview of RFID reader using STR710

AN2399

7.2

Interfacing with STR7xx using I2C peripheral
Due to the fact that the STR7xx microcontroller has a 3.3 voltage supply and the CRX14 device work at 5 V, a level shifter has to be inserted on the I2C bus in order to adjust the voltage levels. Figure 4. Interfacing the I2C bus from 3.3 V to 5 V

The I2C Bus Interface on STR71x provides both multimaster and slave functions, and controls all I2C bus-specific sequencing, protocol, arbitration and timing. It also supports fast I2C mode (400 kHz). For the purpose of this application note, the I2C peripheral works as Master transmitter/receiver. In Master mode, it initiates a data transfer and generates the clock signal. A serial data transfer always begins with a start condition and ends with a stop condition. Both start and stop conditions are generated in master mode by hardware as soon as the Master mode is selected. Data and addresses are transferred as 8-bit bytes, MSB first. The first byte(s) following the start condition contain the address (one in 7-bit mode, two in 10-bit mode). A 9th clock pulse follows the 8 clock cycles of a byte transfer, during which the receiver must send an acknowledge bit to the transmitter. Refer to Figure 5. Figure 5. I2C bus protocol SDA MSB ACK

SC L 1 START CONDITION 2 8 9 STOP CONDITION

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AN2399

Overview of RFID reader using STR710 Finally, I2C peripheral configuration has to be set as follows:

data width: 8-bit Ack bit: enabled Speed config: the user must configure it via I2C_frequency define in device_RFID.h file.

void init_CRX14_I2C(void){ u32 f_RFID=I2C_frequency; /*------------------------------------------------------------------------------------------------------------------------Configure the SDA And the SCL pin of the I2C0 and I2C1 to alternate function Open Drain --------------------------------------------------------------------------------------------------------------------------*/ GPIO_Config (GPIO1,I2C0_SCL,GPIO_AF_OD); GPIO_Config (GPIO1,I2C0_SDA,GPIO_AF_OD); /*------------------------------------------------------------------------------------------------------------------------Configure I2C0 module --------------------------------------------------------------------------------------------------------------------------*/ I2C_Init (I2C0); I2C_FCLKConfig (I2C0); I2C_OnOffConfig (I2C0, ENABLE);//Enable the I2C0 I2C_SpeedConfig (I2C0, f_RFID);//Configure the I2C0 speed I2C_AddressConfig (I2C0,0xA2, I2C_Mode7); //Configure the I2C0 address (to be used specially when this cell has to be adressed) I2C_AcknowledgeConfig (I2C0, ENABLE); //set str7 to send ack when receive data }

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RFID library

AN2399

8

RFID library
RFID library is developed using a 4-layer architecture. This section provides a brief description of the layer functionality. Figure 6. RFID library: the 4 layer structure
RF - ASK Mod

STR710

I2C

CRX14

RF-BPSK mod

Tag

Firmware specifications RFID firmware for STR710 supports SR176 tag Firmware is developed on a 4 layer structure:
RFID reader/writer SR176 Commands CRX14 Commands I2C Commands Application layer: applications dedicated functions RF Commands layer: Initiate(), Select(), Completion(), GetUID(), Read_Block(), Write_Block() Transceiver Commands layer: CRX14 registers management I2C Bus layer: I2C protocol to interface CRX14

8.1

RFID reader/writer: the application layer
The RFID EEPROM memory may be accessed directly using the application layer. It allows read/write operations on RFID EEPROM with different access options. Moreover, the application layer implements the Finite State Machine (FSM) which allows each device to be searched for and selected close to the antenna reader.
/*-----------------------------------------------------------------RFID Application Layer -----------------------------------------------------------------Input: - RFID_Action: 3 bit bit 0: 1=ENABLE 64UID request, 0=DISABLE 64UID request bit 1: 1=ENABLE READ request, 0=DISABLE READ request bit 2: 1=ENABLE WRITE request, 0=DISABLE WRITE request - TX_frame: TX buffer pointer (write operations) - TX_lenght: TX buffer lenght (write operations) - TX_offset: TX offset for write operations - RX_frame: RX buffer pointer (read operations) - RX_lenght: RX buffer lenght (read operations) - RX_offset: RX offset for read operations - RFID_UID: 64 bits RFID UID - RFID_timeout: timeout for RFID polling (number of times STR7 is trying to search tag) Output: - RX_frame: RX buffer pointer (read operations) - RFID_UID: 64 bits RFID UID Return: - Status:

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AN2399
bit0: 1-No tag selected; 0-tag selected bit1: 1-Error on 64UID; 0-no error bit2: 1-Error on READ; 0-no error bit3: 1-Error on WRITE; 0-no error bit4: 1-Error on Completion; 0-no error bit5: 1-Error on RF_OFF; -no error --------------------------------------------------------------------*/ RFID_status = RFID_Handler(RFID_Action, &TX_frame[0], TX_lenght, TX_offset, &RX_frame[0], RX_lenght, RX_offset, &RFID_UID[0], RFID_Polling_timeout);

RFID library

8.1.1

RFID actions
Three main actions are available:

Read: RFID EEPROM Write: RFID EEPROM Get 64-bit UID (unique identifier)

The user can choose actions to perform on the device using the RFID_Action parameter: 3 bits allow each action to be chosen separately.

8.1.2

RFID memory access
Two different ways to access RFID EEPROM in read/write mode are available. The user can choose to:

access (read/write) all 10 words (20 bytes) available on SR176 tag starting from base address 0x0; access (read/write) a portion of memory (one or more words) starting from an offset address. a pointer related to the buffer he want to read/write; the buffer length; the offset where he want to start to read/write.

The following must be provided by the user:

8.1.3

RFID polling
The user can choose how many times to search for a tag device close to the antenna reader using the RFID_Polling_timeout parameter.

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RFID library

AN2399

8.1.4

RFID communication status report
The communication status can be checked using the RFID_Handler return parameter. It returns:

Presence/absence of tag into the space covered from magnetic field. Error on reading/writing RFID EEPROM Error getting 64 bits UID Error on cut-off RF carrier.

In order to access an RFID EEPROM, the application layer function has to implement a Finite State Machine (FSM) as depicted in the following picture: Figure 7. RFID: state transition diagram
POWER-OFF Out of Field READY In Field

INITIATE() ACTIVE

Out of Field Out of Field SELECT(Chip_ID) DESELECTED SELECT(Chip_ID)

SELECT(Chip_ID) SELECTED COMPLETION Out of Field DEACTIVATED

SELECT(Chip_ID) READ_BLOCK() WRITE_BLOCK() PROTECT_BLOCK() GET_PROTECTION()

When invoking the application layer, FSM searches for a tag (for a period of time specified in RFID_Polling_timeout); when a tag device is found, the FSM attempts to recover the tag CHIP_ID using the "Initiate()" command. If the tag responds with its own CHIP_ID the FSM attempts to select it in order to perform actions according the RFID_Action parameter. The FSM performs these actions using the "init_RFID()". It describes all states from POWER OFF to SELECTED. When selected, the application layer FSM uses three functions to perform the requested actions:

GetSR176_64UID(&RFID_UID[0]); ReadSR176_EEPROM(&RX_frame[0],RX_offset,RX_lenght); WriteSR176_EEPROM(&TX_frame[0],TX_offset,TX_lenght);

When all requested actions are performed, the FSM deselects the tag device via a "Completion()" command.

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AN2399

RFID library Every time the RFID_Handler is invoked it powers the antenna with the 13.56 MHz carrier; before exiting, it cuts-off the RF carrier.

8.2

SR176 commands layer
In order to manage the RFID tag, the CRX14 uses a set of commands. They are both used to activate and select each device and to access (read/write or get 64 bits UID) the tag EEPROM. Here are all the functions used for reported RFID tags:

RF_ON(); RF_OFF(); Initiate(&RX_frame[0]); Completion ( &RX_framebuf[0]); Time_Read(); Time_Write();

// power on carrier frequency // power off carrier frequency // search a tag in the field // deselect tag // program time for read // program time for write

Select (RFID_CHIPID,&RX_frame[0]);// activate a tag in the field

ReadBlock (address, &RX_frame[ 0 ]);// read a word WriteBlock (address, &TX_frame[ 0 ], &RX_frame[0]); // write a word

Each RF command has a dedicated 16-bit code (see SR176 and CRX14 datasheet). Tags in the field recognize it and perform the required operation (activation, read, write, deactivation, etc.). RF Commands functions use CRX14 commands to access CRX14 registers. Basically each RF command performs a write operation and a read operation to a CRX14 register.

8.3

CRX14 commands layer
This layer provides all functions needed to interface the STR710 microcontroller with the CRX14 coupler device. CRX14 device uses 6 control registers to communicate both with the microcontroller (via I2C) and the tag (via RF circuitry). Figure 8. CRX14 control register access scheme

I2C

CONTROL REGISTER

RF CIRCUITRY

Depending on which register the user would like to access in read or write mode, several functions are implemented.

17/22

RFID library Table 2.
Address 00h

AN2399 Control registers
Register Parameter Register Length 1 Byte R W 01h Input/Output Frame Register 36 Bytes R W 02h Authenticate Register NA R W 03h Slot Marker Register 1 Byte R 04h 05h ST Reserved ST Reserved NA NA R and W R and W Get the Authentication process Launch the automated anti-collision process from Slot_0 to Slot_15 Return data FFh ST Reserved. Must not be used ST Reserved. Must not be used Transfer PICC answered frame data to host Star t the Authentication process Read parameter register Store and send request frame to the PICC. Wait for PICC answer frame Access W Purpose Set parameter register

8.3.1

CRX14 parameter register access
Figure 9. CRX14 parameter register: write operation
S T A R T R/W Device Select Code Parameter Register Address Register Byte Value S T O P

Bus Master

CRX14 Write Bus Slave

1 0 1 0XXX

00h

data

ACK

ACK

ACK

Figure 10. CRX14 parameter register: read operation
S T A R T R E S T A R T

R/W Device Select Code Parameter Register Address

R/W Device Select Code

NoACK

Bus Master

S T O P

CRX14 Read Bus Slave

1 0 1 0XXX

00h

1 0 1 0XXX

data Register Byte Value

ACK

ACK

ACK

Here are the functions used for parameter register access: int Write_CRX14_PR(UCHAR *DATA) int Read_CRX14_PR(UCHAR *DATA)

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AN2399

RFID library

8.3.2

CRX14 I/O frame register access
The Input/Output Frame Register is a 36-byte buffer that is accessed serially from Byte 0 through to Byte 35 (see Figure 11). It is located at the I²C address 01h. The Input/Output Frame Register is the buffer in which the CRX14 stores the data Bytes of the request frame to be sent to the PICC. It automatically stores the data Bytes of the answer frame received from the PICC. The first Byte (Byte 0) of the Input/Output Frame Register is used to store the frame length for both transmission and reception. Figure 11. CRX14 I/O frame register description
Byte 0 Frame Length Byte 1 1st data Byte B yte 2 2nd data Byte <------------- Request and Answer Frame Bytes exchanged on the RF -------------> 00h No Byte transmitted FFh CRC Error xxh Number of transmitted Bytes B yte 3 ... Byte 34 Byte 35 Last data Byte

When accessed in I²C Write mode , the register stores the request frame Bytes that are to be transmitted to the PICC. Byte 0 must be set with the request frame length (in Bytes) and the frame is stored from Byte 1 onwards. At the end of the transmission, the 16-bit CRC is automatically added. After the transmission, CRX14 waits for the PICC to send back an answer frame. When correctly decoded, the PICC answer frame bytes are stored in the Input/Output Frame Register from Byte 1 onwards. Byte 0 stores the number of bytes received from the PICC. Figure 12. CRX14 I/O frame register: write operation
Bus Master CRX14 Write Bus Slave S T A R T R/W Device Select Code 1 0 1 0 XX X Input/Output Register Address 01h Request Frame Length N N PICC Command Code Data 1 PICC Command Parameter Data 2 PICC Command Parameter PICC Command Parameter Data N S T O P

ACK

ACK

ACK

ACK

ACK

ACK

ACK

When accessed in I²C Read mode, the Input/Output Register sends back the last PICC answer frame Bytes, if any, with Byte 0 transmitted first. The 16-bit CRC is not stored, and it is not sent back on the I²C bus. The Input/Output Frame Register is set to all 00h between transmission and reception. If there is no answer from the PICC, Byte 0 is set to 00h. In the case of a CRC error, Byte 0 is set to FFh, and the data Bytes are discarded and not appended in the register. Figure 13. CRX14 I/O frame register: read operation
R/W S Input/Output Device T Register Select Bus A Address Code Master R T CRX14 1 0 1 0 XX X 01h Read Bus Slave R E S T A R T R/W Device Select Code 1 0 1 0 XXX N Received ACK Frame Length Data1 Answer Frame Data Data 2 Answer Frame Data Answer Frame Data Data N Answer Frame Data ACK ACK ACK ACK NoACK S T O P

ACK

ACK

19/22

RFID library Here are the functions used for I/O Frame register access: int Write_CRX14_IOFR(UCHAR *DATA) int Read_CRX14_IOFR(UCHAR *DATA)

AN2399

8.4

I2C commands layer
The I2C layer provides all the functionalities to access and manage the I2C peripheral on STR710. It is a part of the STR710 library. Some functionality was added in order to receive a status when data is sent or received on the I2C bus; two programmable timeouts (I2C_TIMEOUT_SEND and I2C_TIMEOUT_RECEIVE) inform the application layer about any send/receive failure on I2C bus. Below the code added for I2C_ByteSend and I2C_ByteReceive functions.

8.4.1

I2C_ByteSend_with_status function
/* * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * **** * Function Name : I2C_ByteSend * Description : Send a single byte of data. * Input : I2Cx ( I2C0 or I2C1 ) * Data : the byte to be sent to the slave * Return : status: 0-byte sent, 1-transmission error. * * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ****/ u8 I2C_ByteSend_with_status (I2C_TypeDef *I2Cx, u8 Data) { u8 status=0; u32 timeout=I2C_TIMEOUT_SEND; //Wait until the I2C_BTF bit is set while (((I2Cx->SR1 & 0x08)==0)&&timeout--); if(!timeout) status=1; //Write in the DR register the byte to be sent I2Cx->DR = Data; return status; }

8.4.2

I2C_ByteReceive_with_status function
/* * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * * * Function Name : I2C_ByteReceive * Description : Returns the received byte. * Input : I2Cx ( I2C0 or I2C1 ) * Output : Data ( variable where store read data ) * Return : status: 0-byte sent, 1-transmission error. * * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * ** * **/ u8 I2C_ByteReceive_with_status (I2C_TypeDef *I2Cx, u8 *Data) { u8 status=0; u32 timeout=I2C_TIMEOUT_RECEIVE; //Wait till I2C_BTF bit is set while (((I2Cx->SR1 & 0x08)==0)&&timeout--); if(!timeout) status=1; (*Data)=I2Cx->DR; return status; }

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Revision history

9

Revision history
Table 3.
Date 31-Jan-2008

Document revision history
Revision 1 Initial release. Changes

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